U.S. patent application number 13/846232 was filed with the patent office on 2013-09-19 for light weight proppant with improved strength and methods of making same.
This patent application is currently assigned to OXANE MATERIALS, INC.. The applicant listed for this patent is OXANE MATERIALS, INC.. Invention is credited to Dilip K. Chatterjee, Christopher E. Coker, Andrew Miiller, Jody Pham, Shanghua Wu, Yuming Xie.
Application Number | 20130244914 13/846232 |
Document ID | / |
Family ID | 45874289 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130244914 |
Kind Code |
A1 |
Wu; Shanghua ; et
al. |
September 19, 2013 |
Light Weight Proppant With Improved Strength And Methods Of Making
Same
Abstract
Methods are described to make strong, tough, and lightweight
whisker-reinforced glass-ceramic composites through a
self-toughening structure generated by viscous reaction sintering
of a complex mixture of oxides. The invention further relates to
strong, tough, and lightweight glass-ceramic composites that can be
used as proppants and for other uses.
Inventors: |
Wu; Shanghua; (Houston,
TX) ; Pham; Jody; (Houston, TX) ; Xie;
Yuming; (Houston, TX) ; Chatterjee; Dilip K.;
(Houston, TX) ; Miiller; Andrew; (Houston, TX)
; Coker; Christopher E.; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OXANE MATERIALS, INC. |
Houston |
TX |
US |
|
|
Assignee: |
OXANE MATERIALS, INC.
Houston
TX
|
Family ID: |
45874289 |
Appl. No.: |
13/846232 |
Filed: |
March 18, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/US2011/051712 |
Sep 15, 2011 |
|
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13846232 |
|
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61384875 |
Sep 21, 2010 |
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Current U.S.
Class: |
507/269 ;
264/610; 507/200 |
Current CPC
Class: |
C04B 38/0615 20130101;
C04B 2235/36 20130101; C04B 2235/5445 20130101; C04B 2235/5268
20130101; C04B 2235/77 20130101; C04B 2235/3826 20130101; C04B
2235/96 20130101; C04B 35/185 20130101; C04B 35/803 20130101; C04B
2235/5276 20130101; C04B 2235/322 20130101; C09K 8/80 20130101;
C04B 2235/5409 20130101; C04B 2235/94 20130101; C04B 2235/3418
20130101; C04B 2235/526 20130101; C04B 2235/80 20130101; C04B
35/117 20130101; C04B 35/6261 20130101; C09K 8/805 20130101; C04B
2235/6028 20130101; C04B 2235/528 20130101; C04B 2235/3472
20130101; C04B 2235/724 20130101; C04B 35/62807 20130101; C04B
2235/3217 20130101; C04B 2235/5264 20130101; C04B 2235/3817
20130101; C04B 38/0615 20130101; C04B 35/803 20130101; C04B 38/0054
20130101; C04B 38/0074 20130101 |
Class at
Publication: |
507/269 ;
507/200; 264/610 |
International
Class: |
C09K 8/80 20060101
C09K008/80 |
Claims
1. A method for producing a proppant comprising a. forming a green
body from a green body material comprising i. at least one metal
oxide or precursor thereof that is capable of forming whiskers in
said proppant and as part of said proppant, ii. at least one
amorphous material containing at least one entrapped vaporizable
material, iii. preformed whiskers, and iv. at least one whisker
promoter, optionally in the absence of fluorine or fluorine
compounds; b. reactive sintering said green body under reactive
sintering conditions to form a sintered body comprising whiskers
and at least one amorphous phase.
2-4. (canceled)
5. The method of claim 1, wherein said at least one metal oxide
comprises a first metal oxide and a second metal oxide, wherein
said first metal oxide and said second metal oxide are different
from each other.
6. (canceled)
7. The method of claim 1, wherein said amorphous material comprises
perlite, stober silica, pumice, andesite, scoria, volcanic glasses,
or any combination thereof.
8. The method of claim 7, wherein said vaporizable material
comprises water (H.sub.2O) carbon dioxide (CO.sub.2), sulfur
dioxide (SO.sub.2), hydrogen sulfide (H.sub.2S), nitrogen, argon,
helium, neon, methane, carbon monoxide (CO), hydrogen, oxygen,
hydrogen chloride (HCl), hydrogen fluoride (HF), hydrogen bromide
(HBr), nitrogen oxide (NOx), sulfur hexafluoride (SF.sub.6),
carbonyl sulfide (COS), volcanic gases, or any combination
thereof.
9. The method of claim 1, wherein said amorphous material has a
lower specific gravity than other said green body materials.
10. (canceled)
11. The method of claim 1, wherein said method further comprises
forming said green body around a template so as to encapsulate said
template.
12-16. (canceled)
17. The method of claim 11, wherein said reactive sintering at
least partially converts said template to a template comprising
in-situ whiskers and at least one amorphous phase.
18-19. (canceled)
20. A proppant comprising a sintered body, wherein said sintered
body comprises whiskers and at least one amorphous phase, wherein
said whiskers comprise in-situ whiskers.
21-25. (canceled)
26. The proppant of claim 20, wherein said whiskers have a phase
connectivity of 3.
27-28. (canceled)
29. The proppant of claim 20, further comprising a template.
30-34. (canceled)
35. The proppant of claim 29, wherein said template comprises
whiskers and at least one amorphous phase wherein concentration of
whiskers in said template is different from concentration of
whiskers in said sintered body that is on said template.
36-38. (canceled)
39. A method to prop open subterranean formation fractures
comprising introducing a proppant formulation comprising the
proppant of claim 20 into a subterranean formation.
40-42. (canceled)
43. The method of claim 1, said green body material comprising i.
alumina and/or at least one alumina precursor and a siliceous
material in a ratio to form whiskers in to a glass-ceramic
composite, and ii. at least one amorphous material containing at
least one entrapped vaporizable material, and iii. whiskers, and
iv. at least one whisker promoter in the absence of fluorine or
fluorine compounds; sintering said green body under sintering
conditions to form in situ said glass-ceramic composite comprising
at least one mullite whisker phase and at least one amorphous
phase.
44-45. (canceled)
46. The method of claim 43, wherein said alumina or alumina
precursor has a particle size distribution, d.sub.as, from about
0.5 to about 15, wherein,
d.sub.as={(d.sub.a90-d.sub.a10)/d.sub.a50} wherein d.sub.a10 is a
particle size wherein 10% of the particles have a smaller particle
size, d.sub.50 is a median particle size wherein 50% of the
particles have a smaller particle size, and d.sub.a90 is a particle
size wherein 90% of the particle volume has a smaller particle
size.
47. (canceled)
48. The method of claim 43, wherein the median particle size,
d.sub.a50, of said alumina or alumina precursor is from about 0.01
.mu.m to about 100 .mu.m, wherein d.sub.50 is a median particle
size where 50% of the particles of the distribution have a smaller
particle size.
49-51. (canceled)
52. The method of claim 43, wherein said siliceous material has a
particle size distribution, d.sub.ss, from about 0.5 to about 15,
wherein, d.sub.ss={(d.sub.s90-d.sub.s10)/d.sub.s50} wherein
d.sub.s10 is a particle size wherein 10% of the particles have a
smaller particle size, d.sub.s50 is a median particle size wherein
50% of the particles have a smaller particle size, and d.sub.s90 is
a particle size wherein 90% of the particle volume has a smaller
particle size.
53. (canceled)
54. The method of claim 43, wherein the median particle size,
d.sub.s50, of said siliceous material is from about 0.01 .mu.m to
about 100 wherein d.sub.s50 is a median particle size where 50% of
the particles of the distribution have a smaller particle size.
55-58. (canceled)
59. The method of claim 43, wherein the median particle size,
d.sub.a50, of said amorphous material containing at least one
entrapped vaporizable material is from about 0.01 .mu.m to about
100 .mu.m, wherein d.sub.a50 is a median particle size where 50% of
the particles of the distribution have a smaller particle size.
60. (canceled)
61. The method of claim 43, wherein said ratio to form whiskers in
said glass-ceramic composite is from about 20% SiO.sub.2
material/80% Al.sub.2O.sub.3 or alumina precursor by weight to
about 60% siliceous material/40% alumina or alumina precursor by
weight.
62-66. (canceled)
67. The method of claim 43, wherein said sintering is performed in
the presence of a gas.
68. The method of claim 67, wherein said gas comprises from about
100 ppm to about 100% by weight oxygen.
69-87. (canceled)
88. The method of claim 43, wherein said green body material
further comprises at least one fluxing agent.
89. The method of claim 88, wherein said fluxing agent comprises
nepheline syenite, feldspar, synthetic clay, natural clay or any
combination thereof.
90-92. (canceled)
93. The method of claim 43, wherein the phases of said
glass-ceramic composite comprises 3-3 connectivity for the mullite
whisker phase and the amorphous phase.
94. The method of claim 43, wherein the phases of said
glass-ceramic composite comprises 3-3-0 connectivity for the
mullite whisker phase, the amorphous phase and the unreacted
alumina or alumna precursor.
95. The method of claim 43, wherein the phases of said
glass-ceramic composite comprises 3-3-0 connectivity for the
mullite whisker phase, the amorphous phase and the unreacted
siliceous material.
96. The method of claim 43, wherein the phases of said
glass-ceramic composite comprises 3-3-0 connectivity for the
mullite whisker phase, the amorphous phase and the amorphous
material containing at least one entrapped vaporizable
material.
97-106. (canceled)
107. A glass-ceramic composite material comprising a sintered body
having at least one whisker phase and an amorphous phase and
optionally, at least one crystalline particulate phase.
108. The glass-ceramic composite material of claim 107, wherein
said whisker phase is a mullite whisker phase.
109. The glass-ceramic composite material of claim 107, wherein
said amorphous phase is a ceramics comprising alumina, silica and
any combination thereof.
110. The glass-ceramic composite material of claim 107, wherein
said amorphous phase further comprises unreacted particles of
alumina, alumina precursor, siliceous material, amorphous material
containing at least one entrapped vaporizable material or any
combination thereof.
111. The glass-ceramic composite material of claim 107, further
comprising a template.
112-116. (canceled)
117. The glass-ceramic composite material of claim 107, wherein the
phases of said glass-ceramic composite comprises 3-3-0 connectivity
for the whisker phase, the amorphous phase and the unreacted
alumina or alumna precursor.
118. The glass-ceramic composite material of claim 107, wherein the
phases of said glass-ceramic composite comprises 3-3-0 connectivity
among the whisker phase, the amorphous phase and the unreacted
alumina or alumna precursor.
119. The glass-ceramic composite material of claim 107, wherein the
phases of said glass-ceramic composite comprises 3-3-0 connectivity
among the whisker phase, the amorphous phase and the amorphous
material containing at least one entrapped vaporizable
material.
120. The glass-ceramic composite material of claim 107, wherein the
phases of said glass-ceramic composite comprises 3-3-0-0-0
connectivity for the whisker phase, the amorphous phase, the
unreacted alumina material, the unreacted siliceous material, and
the amorphous material containing at least one entrapped
vaporizable material.
121-126. (canceled)
127. A method for producing a proppant comprising a. forming a
green body from a green body material comprising i. at least one
metal oxide or precursor thereof that is capable of forming
whiskers in said proppant and as part of said proppant, and ii. at
least one amorphous material containing at least one entrapped
vaporizable material, and iii. optionally preformed whiskers, and
iv. at least one whisker promoter, optionally in the absence of
fluorine or fluorine compounds; and v. at least one carbide or
metal carbide, b. reactive sintering said green body under reactive
sintering conditions to form a sintered body comprising in-situ
whiskers and at least one amorphous phase.
128. (canceled)
129. The proppant of claim 20, wherein said sintered body comprises
whiskers, at least one glassy phase, and at least one amorphous
phase.
130. The proppant of claim 129, wherein said sintered body further
comprises at least one carbide or metal carbide.
131-138. (canceled)
139. The proppant of claim 20, comprising a sintered sphere having
a Krumbein sphericity of at least about 0.5 and a roundness of at
least about 0.4, and wherein said sphere comprises a) a plurality
of ceramic whiskers or oxides thereof and b) a glassy phase and c)
optionally at least one non-whisker crystalline phase and d)
optionally a plurality of microspheres, wherein said sintered
sphere has a diameter of from about 90 microns to 2,500 microns,
and said sintered sphere has a specific gravity of from 0.8 g/cc to
about 3.8 g/cc, and said proppant has a crush strength of from
about 1,000 psi or greater, and wherein said proppant includes one
or more of the following characteristics: 1) said glassy phase is
present in an amount of at least 10% by weight, based on the weight
of the proppant; 2) said ceramic whiskers have an average length of
less than 3.2 microns; 3) said ceramic whisker have an an average
width of less than 0.35 micron; 4) said ceramic whiskers have a
whisker length distribution, d.sub.as, of about 8 or less, wherein,
d.sub.as={(d.sub.a90-d.sub.a10)/d.sub.a50} wherein d.sub.a10 is a
whisker length wherein 10% of the whiskers have a smaller length,
d.sub.a50 is a median whisker length wherein 50% of the whiskers
have a smaller whisker length, and d.sub.a90 is a whisker length
wherein 90% of the whiskers have a smaller whisker length; 5) said
proppant having a specific gravity of from 1.6 to 1.8 with a crush
strength of at least 2000 psi; 6) said proppant having a specific
gravity of from 1.8 to 2 with a crush strength of at least 3000
psi; 7) said proppant having a specific gravity of from 2 to 2.1
with a crush strength of at least 5,000 psi; 8) said proppant
having a specific gravity of from 2.25 to 2.35 with a crush
strength of at least 8,000 psi; 9) said proppant having a specific
gravity of from 2.5 to 3.2 with a crush strength of at least 12,000
psi; 10) said proppant having a specific gravity of from 2.5 to 3.2
with a crush strength of at least 18,000 psi; 11) said proppant
having a combined clay amount and cristobalite amount of less than
20% by weight of proppant; 12) said proppant having an free
alpha-alumina content of at least 5% by weight of said proppant;
13) said proppant having an HF etching weight loss of less than 35%
by weight of said proppant; 14) said proppant having said
microspheres present as hollow glass microspheres having a particle
size distribution, d.sub.as, of from about 0.5 to about 2.7,
wherein, d.sub.as={(d.sub.a90-d.sub.a10)/d.sub.a50} wherein
d.sub.a10 is a particle size wherein 10% of the particles have a
smaller particle size, d.sub.a50 is a median particle size wherein
50% of the particles have a smaller particle size, and d.sub.a90 is
a particle size wherein 90% of the particle volume has a smaller
particle size; 15) said proppant having microspheres present
wherein said microspheres are uniformly present in said proppant or
in a layered region of said proppant; 16) said ceramic whiskers are
present in an amount of from 5% to 60% by weight of said proppant.
17) said proppant has a combined clay amount and cristobalite
amount of less than 20% by weight of proppant and said mullite
whiskers are present in an amount of 60% or more by weight of said
proppant; 18) said proppant has a high whisker distribution density
based on individual whiskers present in the proppant (# of whiskers
per mg of proppant); 19) said proppant has a unimodal whisker
distribution; 20) said proppant has at least two layers that form a
laminate structure; 21) said proppant has at least a first layer
and a second layer that form a laminate structure wherein the
average length of said whiskers in said first layer compared to
said second layer is different; 22) said proppant has at least a
first layer and a second layer that form a laminate structure
wherein the average width of said whiskers in said first layer
compared to said second layer is different; 23) said whiskers in
said proppant are less euhedral and more anhedral; 24) said
proppant has at least one radial region of first whiskers and at
least one region of second whiskers, wherein the average whisker
length is different by at least 10%; 25) said proppant has at least
one radial region of first whiskers and at least one region of
second whiskers, wherein the average whisker width is different by
at least 10%; 26) said proppant has a major phase of whiskers of
less than one micron and a secondary minor phase of whiskers of one
micron or higher; and/or 27) said ceramic whiskers have a whisker
length distribution having d.sub.a90, which is a whisker length
wherein 90% of the whiskers have a smaller whisker length, of less
than 12 microns.
140-146. (canceled)
Description
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(e) of prior U.S. Provisional Patent Application No.
61/384,875, filed Sep. 21, 2010, which is incorporated in its
entirety by reference herein.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to methods to make strong,
tough, and lightweight whisker-reinforced glass-ceramic composites.
The method can involve forming a self-toughening structure
generated by viscous reaction sintering of a complex mixture of
oxides. The whisker-reinforced glass-ceramic preferably is strong,
tough, and/or lightweight. The present invention further relates to
strong, tough, and lightweight glass-ceramic composites used as
proppants and for other uses including, but not limited to, armor
plating, electronic, optical, high-temperature structural materials
and applications, as a low dielectric constant substrate material
in high-performance packaging applications; or window materials for
the mid-infrared range.
[0003] The use of certain inorganic whiskers and fibers to
reinforce glasses, glass ceramics, and ceramics has been known and
practiced. Whiskers are typically characterized as relatively
short, single-crystal fibers of small diameter, typically less than
100 microns. Fibers on the other hand can be multicrystalline or
amorphous and are long enough to be used in woven or other types of
interlocking networks, filter tows or fabric. Whiskers are
typically incorporated in a selected glass or ceramic matrix as a
randomly dispersed phase.
[0004] Fibers are more commonly used in an oriented or interlocking
alignment. Load transfer by the matrix to the fibers through shear
is the means by which fibers strengthen glass or ceramic bodies.
The load transfers stress from the glass or ceramic matrix to the
relatively long and high modulus fibers. The fibers can also impede
crack initiation and propagation through the matrix material.
[0005] Whiskers can provide strengthening in a similar manner, but
load transfer to the whiskers by the matrix is more limited because
of the limited length and aspect ratio of the whiskers. Because
whiskers are relatively short, they cannot carry as much load
compared to the longer fibers. It is more difficult to take full
advantage of the intrinsic strength of whiskers compared to fibers
for this reason. Whisker reinforcement in ceramic and glass-ceramic
materials is often used to increase toughness. A toughened ceramic
material improves crack resistance, increases fatigue lifetime
and/or provides a noncatastrophic mode of failure. Non-catastrophic
failure is highly desirable in applications where repair can be
facilitated and information about failure conditions is
important.
[0006] Silicon carbide, silicon nitride, alumina, and carbon
whiskers have all been used to reinforce non-metallic matrices. For
example, U.S. Pat. No. 4,324,843 describes SiC fiber reinforced
glass-ceramic composite bodies where the glass-ceramic matrix is an
aluminosilicate composition. U.S. Pat. No. 4,464,192 describes
whisker-reinforced glass-ceramic composites of an aluminosilicate
composition. U.S. Pat. No. 4,464,475 describes similarly reinforced
glass-ceramics with barium osumilite as the predominant crystal
phase.
[0007] The use of whiskers in ceramic composites can improve the
fracture toughness of the ceramic composite because of the
whiskers' ability to absorb cracking energy. The whiskers appear to
toughen the composites by deflecting crack propagation, bridging
cracks and by whisker "pull-out." Whisker "pull-out" occurs when
the ceramic matrix at the whisker-matrix interface cracks. When a
crack-front propagates into the composite, many of the whiskers can
bridge the crack line and extend into the ceramic matrix
surrounding the crack. For the crack to grow or propagate through
the ceramic, these whiskers must be either broken or pulled out of
the matrix. As these whiskers are pulled out of the matrix, they
provide a bridging force across the faces of the crack, reducing
the intensity of the stress at the crack tip. In this way, the
whiskers absorb the energy that would propagate the crack. Whisker
pull-out reduces the tendency of a composite to crack and also
inhibits crack propagation. U.S. Pat. Nos. 4,543,345; 4,569,886;
and 4,657,877 relate to silicon carbide whisker-reinforced ceramic
composites.
[0008] Perlite (sometimes spelled pearlite) is an amorphous
volcanic glass that has a relatively high water content. Perlite is
formed by the hydration of obsidian, a naturally occurring volcanic
glass formed as an extrusive igneous rock. The typical chemical
composition of perlite is SiO.sub.2:69-72%, Al.sub.2O.sub.3:12-18%,
K.sub.2O:3-4.5%, Na.sub.2O:3-4.5%, CaO:0.1-0.2%, MgO:0.2-0.5%,
Moisture: 2-4%, where all percentages are weight percent. Perlite
has the unusual property of greatly expanding when sufficiently
heated. When perlite reaches temperatures of 850-900.degree. C., it
softens (since it is a glass). Water trapped in the structure of
the perlite vaporises and escapes, causing an expansion of the
perlite to 7-16 times its original volume. The expansion process of
perlite requires rapid heating (around 900.degree. C./min) and then
removal of the particle from the heat zone. The expansion creates
countless tiny bubbles leading to very low density. Special heating
approaches such as steam or flame heating are usually employed to
achieve the required heating rate. In a typical industrial furnace
with a heating rate less than 200.degree. C./min, the raw perlite
cannot be expanded. Since perlite is a form of natural glass, it is
chemically inert and has a pH around 7. Unexpanded perlite has a
bulk density around 1.1 g/cm.sup.3 and expanded perlite has a bulk
density of about 30-150 kg/m.sup.3. Expanded perlite is used in a
variety of industrial applications as a filler because of its
ability to expand and fill void spaces and because of its
relatively low specific gravity. The majority of the applications
of perlite are in building construction in the expanded form due to
its low density, low thermal and acoustical conductivity, and
non-flammability. Perlite is used as a loose fill insulation in
masonry construction, an aggregate in concrete, an aggregate in
Portland cement and an aggregate in gypsum plasters. Perlite is a
relatively low cost material compared to other materials used in
the formulation of glass-ceramic composites. The cost of perlite is
approximately the same as sand. Perlite has been used in proppants
and other ceramics primarily for its relatively low specific
gravity. U.S. Patent Application Nos. 2005/0096207, 2006/0162929
and 2006/0016598, and U.S. Pat. No. 7,160,844 describe the use of
perlite as a filler in proppants. U.S. Patent Application Nos.
2006/0177661 and 2009/0038797 describe the use of perlite as a
lightweight template in proppants.
[0009] The production of glass-ceramic composites with whisker or
fiber reinforcement usually involves dispersion of the whiskers or
fibers in a green body prior to firing or sintering the green body
to produce the final glass-ceramic reinforced composite. The
methods in U.S. Pat. Nos. 4,543,345; 4,569,886; and 4,657,877
recite preformed whiskers dispersed in a ceramic precursor prior to
forming a green body for sintering. Processes involving dispersion
of preformed whiskers in a green body material have been difficult
to successfully implement because whiskers have a tendency to
agglomerate resulting in non-uniform concentrations of whiskers
throughout the green body and ultimately in the ceramic composite.
Non-uniform whisker concentration results in significant variance
in the extent of reinforcement and toughening. As the percent by
weight of whiskers in a green body material increases,
agglomeration and clumping of whiskers increases. In addition,
powdered ceramic precursor material may become imbedded within
clumped whiskers. After sintering, the presence of these powders
can significantly weaken the whiskers' reinforcing abilities.
[0010] A variety of granular particles are widely used as propping
agents to maintain permeability in oil and gas formations. Three
grades of proppants are typically employed: sand, resin-coated sand
and ceramic proppants. Conventional proppants exhibit exceptional
crush strength but also extreme density. A typical density of
ceramic proppants exceeds 100 pounds per cubic foot. Proppants are
materials pumped into oil or gas wells at extreme pressure in a
carrier solution (typically brine) during the hydrofracturing
process. Once the pumping-induced pressure is removed, proppants
"prop" open fractures in the rock formation and thus preclude the
fracture from closing. As a result, the amount of formation surface
area exposed to the well bore is increased, enhancing recovery
rates. Proppants also add mechanical strength to the formation and
thus help maintain flow rates over time. Proppants are principally
used in gas wells, but do find applications in oil wells.
[0011] Relevant quality parameters include: particle density (low
density is desirable), crush strength and hardness, particle size
(value depends on formation type), particle size distribution
(tight distributions are desirable), particle shape (spherical
shape is desired), pore size (value depends on formation type and
particle size, generally smaller is better), pore size distribution
(tight distributions are desirable), surface smoothness, corrosion
resistance, temperature stability, and hydrophilicity
(hydro-neutral to phobic is desired). Lighter specific gravity
proppants can be desirable, which are easier to transport in the
fracturing fluid and therefore can be carried farther into the
fracture before settling out and which can yield a wider propped
fracture than higher specific gravity proppants.
[0012] Proppants used in the oil and gas industry are often sand
and man-made ceramics. Sand is low cost and light weight, but low
strength; man-made ceramics, mainly bauxite-based ceramics or
mullite based ceramics are much stronger than sand, but heavier.
Ceramic proppants dominate sand and resin-coated sand on the
critical dimensions of crush strength and hardness. They offer some
benefit in terms of maximum achievable particle size, corrosion and
temperature capability. Extensive theoretical modeling and
practical case experience suggest that conventional ceramic
proppants offer compelling benefits relative to sand or
resin-coated sand for most formations. Ceramic-driven flow rate and
recovery improvements of 20% or more relative to conventional sand
solutions are not uncommon.
[0013] Ceramic proppants were initially developed for use in deep
wells (e.g., those deeper than 7,500 feet) where sand's crush
strength is inadequate. In an attempt to expand their addressable
market, ceramic proppant manufacturers have introduced products
focused on wells of intermediate depth.
[0014] Resin-coated sands offer a number of advantages relative to
conventional sand. First, resin coated sand exhibits higher crush
strength than uncoated sand given that resin-coating disperses load
stresses over a wider area. Second, resin-coated sands are "tacky"
and thus exhibit reduced "proppant flow-back" relative to
conventional sand proppants (e.g. the proppant stays in the
formation better). Third, resin coating typically increases
sphericity and roundness thereby reducing flow resistance through
the proppant pack.
[0015] Ceramics are typically employed in wells of intermediate to
deep depth. Shallow wells typically employ sand or no proppant.
SUMMARY OF THE INVENTION
[0016] A feature of the present invention is to provide a composite
having a whisker phase and an amorphous phase.
[0017] A feature of the present invention is to provide a
glass-ceramic composite having a mullite whisker phase and an
amorphous phase.
[0018] A further feature of the present invention is to provide a
glass-ceramic composite having a mullite whisker phase and an
amorphous phase in which the whiskers are present in a three
dimensional non-woven structure.
[0019] A further feature of the present invention is to provide a
glass-ceramic composite having a mullite whisker phase and an
amorphous phase in which the whiskers are uniformly dispersed.
[0020] A further feature of the present invention is to provide a
glass ceramic composite with a uniform dispersion of relatively
small pores with substantially spherical shape and a smooth
interior pore surface.
[0021] A further feature of the present invention is to provide a
method for making a composite having a whisker phase and an
amorphous phase, wherein the whisker phase is pre-formed and/or
formed in-situ.
[0022] A further feature of the present invention is to provide a
method for making a glass-ceramic composite having a mullite
whisker phase and an amorphous phase in which the mullite whiskers
are pre-formed and/or formed in situ.
[0023] A further feature of the present invention is to provide a
method for making strong, tough, and lightweight glass-ceramic
matrix composites through a self-toughening structure generated by
viscous reaction sintering of a complex mixture of oxides.
[0024] A further feature of the present invention is to provide a
method for making strong, tough, and/or lightweight glass-ceramic
matrix composites through a self-toughening structure that can be
generated by producing a uniform dispersion of relatively small
pores with substantially spherical shape and a smooth interior pore
surface, and this can be done by liberating entrapped water and/or
other vaporizable materials from an amorphous material, for
instance, during a controlled viscous reaction sintering of a
complex mixture of oxides.
[0025] A further feature of the present invention is to provide a
method for making strong, tough, and/or lightweight glass-ceramic
matrix composites including an optional fluxing agent.
[0026] A further feature of the present invention is to provide a
glass-ceramic composite, such as in the form of a proppant, with
superior crush strength.
[0027] A further feature of the present invention is to provide a
proppant having a superior balance of crush strength and/or
buoyancy as shown by specific gravity.
[0028] A further feature of the present invention is to provide a
glass-ceramic composite, such as in the form of a proppant, with
superior resistance to chemical attack, for instance, from acids
and/or aqueous salt solutions.
[0029] A further feature of the present invention is to provide a
glass-ceramic composite, such as in the form of a proppant, with a
smooth external surface and containing pores with a high degree of
sphericity and a smooth surface on the interior surface of the
pores.
[0030] A further feature of the present invention is to provide a
glass-ceramic composite, such as in the form of a proppant, with
high strength, low specific gravity, and/or high chemical
resistance at low cost.
[0031] A further feature of the present invention is to provide a
proppant that can overcome one or more of the disadvantages
described above.
[0032] To achieve one or more features of the present invention,
the present invention relates to a method to produce a material,
such as a composite, by forming a green body. The green body can be
formed from a green body material. The green body material can
include at least one metal oxide (such as a first metal oxide and a
second metal oxide, wherein the first metal oxide is different from
the second metal oxide). The metal oxides are preferably capable of
forming whiskers in-situ, for instance, from or due to reactive or
reaction sintering. The in-situ whiskers can be ceramic whiskers,
mineral whiskers, metal oxide whiskers, or any combination thereof.
The green body material further includes pre-formed whiskers that
can be ceramic pre-formed whiskers, mineral pre-formed whiskers,
and/or metal oxide pre-formed whiskers. The green body material
further includes at least one whisker promoter. The green body may
further include at least one amorphous material that contains
entrapped water and/or other vaporizable materials. The amorphous
material may have a specific gravity that is lower that the other
green body materials thereby contributing to a lower proppant
specific gravity. The method then involves sintering the green body
under sintering conditions that preferably are reactive sintering
conditions in order to form a material or sintered body having at
least one whisker phase and at least one amorphous phase. An
optional fluxing agent can be provided to enhance mixing of and
sintering of the green body material. The method can further
involve controlling the sintering process to liberate water or
other materials entrapped in an amorphous material in a controlled
manner such that the liberated gas forms a relatively small number
of substantially uniformly distributed pores having a substantially
spherical shape in the sintered body.
[0033] An example of a method for producing a self-toughened
high-strength glass-ceramic composite can be as follows. The method
can include forming a green body from a green body material. The
green body material can include: [0034] a) alumina and/or at least
one alumina precursor and a siliceous material in a controlled
ratio to form mullite whiskers in a glass-ceramic composite, and
[0035] b) a minor amount of mullite whiskers, and [0036] c) at
least one whisker promoter in the absence of fluorine or fluorine
compounds, and [0037] d) perlite and/or at least one amorphous
material containing at least one entrapped vaporizable material
such as water, and [0038] e) optionally, at least one fluxing agent
such as nepheline syenite, feldspar, clay, and/or similar
materials. The method can include sintering the green body under
sintering conditions to form in situ a glass-ceramic composite with
at least one mullite whisker phase and at least one amorphous
phase. The method can further include controlling the sintering
conditions such that the water in the perlite and/or the
vaporizable material in an amorphous material is liberated to form
a relatively small number of substantially uniformly distributed
pores having substantially spherical shape in the sintered
body.
[0039] The present invention further relates to materials,
composites, or particles of the present invention. The material of
the present invention has a whisker phase and at least one
amorphous phase. The material can further include pre-formed
whiskers. The in-situ whiskers can be uniformly distributed
throughout the material. The in-situ whiskers can have a
concentration that is uniform throughout the material. As an
option, there is no agglomeration or clumping of the pre-formed
and/or in-situ whiskers in the material. The whiskers can be
present in a three-dimensional non-woven structure or pattern in
the material. The whisker phase of the pre-formed and/or in-situ
whiskers can be a continuous phase, or can be a non-continuous
phase, depending on the concentration of the whiskers that make the
whisker phase. The amorphous material, such as perlite, can have a
lower specific gravity than the other materials in the green body
material. The material of the present invention can include a
relatively small number of substantially uniformly distributed
pores having substantially spherical shape in the sintered
body.
[0040] The present invention further provides a new and improved
propping agent, and a method of making and use thereof, that
overcomes the above-referenced problems and others. The present
invention also relates to a ceramic proppant having a unique
microstructure that includes whiskers arranged in a random
alignment, and optionally having reduced density, and/or improved
strength. The whiskers can be employed to reinforce the ceramic
proppant and/or dissipate energy during crack propagation. The
microstructure can also include anisotropic crystals, for example,
crystals elongated along the C-axis. The proppant can have a
reduced density such that the proppant has a low specific gravity
while optionally maintaining improved mechanical and/or flexural
strength. As an option, the present invention provides a proppant
having substantially spherical shape and a smooth exterior surface.
The present invention can include a relatively small number of
substantially uniformly distributed pores having substantially
spherical shape in the sintered body where such pores can
contribute to reducing the density of the proppant. The small size,
uniform distribution, and/or substantially spherical shape of the
pores contribute to improved toughness, strength and/or crush
resistance of the proppant. The present invention can provide a
proppant having improved resistance to chemical attack, such as
from acids and/or aqueous salt solutions.
[0041] The present invention further relates to a method of
producing a ceramic proppant that employs a reactive sintering
process to form whiskers in-situ through the chemical reaction of
raw materials and, optionally, to form a relatively small number of
substantially uniformly distributed pores having substantially
spherical shape in the ceramic proppant, such as through the use of
controlled sintering of amorphous materials having inclusions of a
vaporizable material. Pores may also be produced through the use of
pore formers which form pores through chemical reaction and/or
thermal decomposition to form a gas. The method allows the
porosity, such as pore size, pore size distribution, and/or pore
shape, of the proppant, to be controlled. Alterations to the
porosity can have a large impact on reducing the specific gravity
while maintaining mechanical and/or flexural strength.
[0042] The proppant can be used in any application suitable for a
proppant. The present invention accordingly relates to a method to
prop open subterranean formation fractions using the proppant.
[0043] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only and are intended to provide a further
explanation of the present invention, as claimed.
[0044] The accompanying drawings, which are incorporated in and
constitute a part of this application, illustrate some of the
embodiments of the present invention and together with the
description, serve to explain the principles of the present
invention.
BRIEF DESCRIPTION OF DRAWINGS
[0045] FIG. 1 is a schematic showing the structure of a proppant
with a hollow template.
[0046] FIG. 2 is a SEM image showing the microstructure of in-situ
formed microwhiskers on the free and fracture surfaces of a
proppant.
[0047] FIG. 3 is a SEM image showing evidence of pull-out of
micro-whiskers in a composite structure.
[0048] FIG. 4 is a SEM image showing the texture fracture surface
of a composite after leaching out the glass phase.
[0049] FIG. 5 is a chart showing specific gravity and crush
strength of proppants made with varying amounts (in wt %) of
alumina, cenospheres and perlite.
[0050] FIG. 6 is an X-ray diffraction pattern showing corundum
(a-Alumina) and mullite for a composite made with 50 wt %
Al.sub.2O.sub.3, 30 wt % Cenosphere, and 20 wt % Perlite.
[0051] FIG. 7 is a comparison of alumina-cenosphere compositions
(CAM) with a selected alumina-cenosphere-perlite composition (all
percents are wt %).
[0052] FIG. 8 is a SEM image showing the fractured surface of a
split-tested pellet with composition: 50 wt % Al.sub.2O.sub.3-30 wt
% Cenospheres-20 wt % Perlite.
[0053] FIG. 9 is a SEM image showing the fractured surface of a
split-tested pellet with composition: 50 wt % Al.sub.2O.sub.3-50 wt
% Cenospheres.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0054] The present invention relates to a material (e.g.,
particles, agglomerates, an article, and the like) that includes
whiskers and an amorphous phase. The material can be referred to as
a sintered body. The material can be a composite of two or more
materials, which, in this case, would be at least the whiskers and
the amorphous phase present in the same material. The material can
have a smooth and continuous surface. Optionally, the amorphous
phase may contain pores with a smooth interior surface that are
present in the amorphous phase and within the smooth exterior
surface of the material. Optionally, at least one crystalline
particulate phase is present in the material. The material of the
present invention can include whiskers that are in a matrix that
includes at least one metal oxide, such as silica. The matrix can
include other components or ingredients as mentioned herein. The
matrix is preferably at least amorphous (e.g., having an amorphous
phase). For purposes of the present invention, the material can
include whiskers or a whisker phase and an amorphous phase, for
instance, that can include silica and/or other metal oxides.
[0055] For purposes of the present invention, the material of the
present invention will be described in terms of its preferred form
or shape, namely particles that can be used in a variety of end use
applications, such as for proppant uses in hydrocarbon recovery.
While the preferred shape and preferred materials of the present
invention are described in detail below, it is to be understood
that this is simply for exemplary purposes and in no way limits the
scope of the present invention with respect to shape, materials,
and/or end uses. While the term "proppant" is used at times in the
application, it is understood that this term is not meant to be
limited to its end use application, but for purposes of the present
invention, it is to be understood that the proppant or particles,
which are used as proppants, can be used in any end use application
where ceramic material is useful.
[0056] Also, for purposes of the present invention, it is to be
understood that the term "whiskers" as used herein can include what
is traditionally known as whiskers, namely a length of less than 1
micron, or can include what is traditionally know as "fibers,"
namely a length of 1 micron or more, or both.
[0057] The material or particles of the present invention can be
characterized as composites and these composites can be
glass-ceramic composites due to the glassy phase or glassy
components present in the composite and due to the ceramic phase or
ceramic components present in the composite.
[0058] The preferred material or particles of the present invention
have whiskers distributed in a matrix (e.g., glassy matrix),
wherein the matrix includes at least one metal oxide, such as
silica. The matrix can be considered amorphous or to have the
amorphous phase. Preferably, the amorphous phase is present
throughout the material and preferably distributed in a uniform
manner. The whiskers are preferably distributed in a glassy matrix.
The glassy matrix can include at least one metal oxide, such as
silica or a silicon-containing oxide. The glassy matrix may contain
small pores that are uniformly distributed in the amorphous phase
and can be essentially spherical and can possess a smooth interior
surface. The exterior surface of the material or particles can have
a smooth and continuous exterior surface.
[0059] In more detail, the material of the present invention can
include from about 0.01% by weight to about 99.9% by weight (based
on the weight of the material) of the matrix or amorphous phase.
The matrix or amorphous phase can include a silicon-containing
oxide (e.g., silica), and optionally at least one iron oxide;
optionally at least one potassium oxide; optionally at least one
calcium oxide; optionally at least one sodium oxide; optionally at
least one titanium oxide; and/or optionally at least one magnesium
oxide, or any combinations thereof. Preferably, the matrix or
amorphous phase contains one or more or each of these optional
oxides, such as in various amounts. Preferably, the
silicon-containing oxide is the major component by weight in the
matrix or amorphous phase, such as where the silicon-containing
oxide is present in an amount of at least 75% by weight, at least
85% by weight, at least 90% by weight, at least 95% by weight, at
least 97% by weight, at least 98% by weight, at least 99% by weight
(such as from 75% by weight to 99% by weight, from 90% by weight to
95% by weight, from 90% by weight to 97% by weight) based on the
weight of the matrix or amorphous phase. Exemplary oxides that can
be present in the amorphous phase include, but are not limited to,
SiO.sub.2, Al.sub.2O.sub.3, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4,
K.sub.2O, CaO, Na.sub.2O, TiO.sub.2, and/or MgO. It is to be
understood that, for purposes of the present invention, other
metals and/or metal oxides can be present in the matrix or
amorphous phase.
[0060] The material can include one or more minerals and/or ores,
one or more clays, and/or one or more silicates, and/or one more
solid solutions. The minerals or ores can be aluminum-containing
minerals or ores and/or silicon-containing minerals or ores. These
can be present as particulates. These additional components can be
present as at least one crystalline particulate phase that can be
non-continuous phase or continuous phase in the material. More
specific examples include, but are not limited to, alumina,
aluminum hydroxide, bauxite, gibbsite, boehmite or diaspore, ground
cenosheres, perlite, stober silica, fly ash, unreacted silica,
silicate materials, quartz, feldspar, zeolites, bauxite and/or
calcined clays. These components in a combined amount can be
present in the material in an amount, for instance, of from 0.001
wt % to 10 wt % or more, such as from 0.01 wt % to 10 wt %, 0.1 wt
% to 8 wt %, 0.5 wt % to 5 wt %, 0.75 wt % to 5 wt %, 0.5 wt % to 3
wt %, 0.5 wt % to 2 wt % based on the weight of the material. These
additional components can be uniformly dispersed throughout the
matrix or amorphous phase (like filler is present in a matrix as
discrete particulates). As an option, the matrix or amorphous phase
does not contain or contains significantly low amounts of halides.
For example, as an option, the matrix or amorphous phase contains
0.1 wt % or less of a halide (e.g., F, Cl, Br, I) or a halide
compound, such as 0.01 wt % or less, 0.001 wt % or less, or 0.0001
wt % or less, and preferably, 0 wt % of a halide, based on the
weight of the amorphous phase. As an option, the matrix or
amorphous phase contains low amounts or 0 wt % of fluorine, but
with no limitations on the amounts of the other halides. In this
option, the fluorine amount can be the halide amount as mentioned
above. It is understood that these weight percents are based on the
elemental halide, such as elemental fluorine, and further based on
the total weight of the amorphous phase or matrix.
[0061] The material can include at least one amorphous material
that contains an entrapped vaporizable material such as water. As
an option, the entrapped vaporizable material can be present in
other parts of the material, such as in the crystalline phase, if
present. The amorphous material that contains an entrapped
vaporizable material can have a lower specific gravity than the
other green body materials. Examples of the amorphous material
include perlite, stober silica, pumice, andesite, scoria, volcanic
glasses or any combination thereof. The amorphous material that
contains an entrapped vaporizable material, such as water, can be
present by weight in the matrix or amorphous phase in an amount of
at least 5% by weight, at least 10% by weight, at least 15% by
weight, at least 20% by weight, at least 25% by weight, at least
30% by weight, at least 35% by weight, at least 40% by weight, such
as from 5% by weight to 40% by weight, from 10% by weight to 35% by
weight, from 15% by weight to 25% by weight. The entrapped
vaporizable material may comprise vaporizable water (H.sub.2O),
carbon dioxide (CO.sub.2), sulfur dioxide (SO.sub.2), hydrogen
sulfide (H.sub.2S), nitrogen, argon, helium, neon, methane, carbon
monoxide (CO), hydrogen, oxygen, hydrogen chloride (HCl), hydrogen
fluoride (HF), hydrogen bromide (HBr), nitrogen oxide (NOx), sulfur
hexafluoride (SF.sub.6), carbonyl sulfide (COS), volcanic gases or
any combination thereof.
[0062] In the present invention, the matrix or amorphous phase can
be a continuous phase present in the material of the present
invention.
[0063] One component that can be further present in the material or
in the matrix or amorphous phase can be B.sub.2O.sub.3 and/or one
or more transition metal oxides, such as Fe.sub.2O.sub.3,
TiO.sub.2, CoO, and/or NiO, or any combinations thereof. The
B.sub.2O.sub.3 and/or transition metal oxides can be present in the
matrix or amorphous phase in various amounts, such as in low or
trace amounts, for instance, 1 wt % or less, such as 0.5 wt % or
less, such as 0.25 wt % or less, such as 0.01 wt % to 0.001 wt %,
based on the weight of amorphous phase.
[0064] As an option, one or more carbides, such as SiC and/or other
forms can be present in the material (e.g., sintered body). The
carbide can be present as particles, particulates, and/or fibers
and/or whiskers. As an option, the carbide in part, or in its
entirety, is not used as a pore former, but is used as a
particulate or fiber or whisker that remains as part of the
material (e.g. sintered body). This can be achieved, for instance,
by sintering in an inert atmosphere (and not an oxygen containing
atmosphere). This controlled sintering avoids the carbide reacting
and forming a gas bubble. The carbide in this form can be present
in any amount, such as from about 0.01% by weight to 25% by weight
or more, based on the weight of the material (e.g. sintered body).
The material (e.g., sintered body) can be a solid material (i.e.,
no template or no hollow template in the interior) or the material
can have such a template. The material can be porous or non-porous.
The material can have microspheres (pre-formed or in situ formed)
as an option. The range of SiC particle size used in the green body
material can have effects on both microsphere placement and/or size
and strength enhancement in the composite proppant product. The SiC
or other carbide powder used in the green body material should have
a small size with a large enough surface area to allow the
oxidation to proceed as desired. SiC particles can have a particle
size distribution with d.sub.fs from about 0.5 to about 5.0 and
from about 0.5 to about 1.5, wherein,
d.sub.fs={(d.sub.f90-d.sub.f10)/d.sub.f50} wherein d.sub.f10 is a
particle size wherein 10% (by volume) of the particles have a
smaller particle size, d.sub.f50 is a median particle size wherein
50% (by volume) of the particles have a smaller particle size, and
d.sub.f90 is a particle size wherein 90% (by volume) of the
particles have a smaller particle size. The median particle size,
d.sub.f50, of the SiC is from about 0.01 .mu.m to about 100 .mu.m
or from about 0.2 .mu.m to about 5 .mu.m, wherein d.sub.f50 is a
median particle size where 50% (by volume) of the particles of the
distribution have a smaller particle size. The SiC can be present
in an amount of from about 0.01 to about 50 wt %, by weight of the
green body or from about 0.01 to about 10 wt %, by weight of the
green body. The silicon carbide can have a surface area (BET) of
from about 0.5 m.sup.2/g to about 100 m.sup.2/g or from about 8
m.sup.2/g to about 15 m.sup.2/g. These properties can remained in
the sintered body as well or be within 10% or within 20% or within
40% of these parameters.
[0065] As an option, the matrix or amorphous phase can have no
pores in this phase. As an option, the matrix or amorphous phase
can be porous.
[0066] With regard to the whiskers, the whiskers can be considered
to be in the form of needles, for instance, as shown in some of the
figures of the present invention. The whiskers can be mineral-based
or metal oxide-based whiskers or can be considered whiskers formed
of one or more minerals and/or metal oxides. Preferably, the
whiskers are mullite whiskers (e.g., needle-shaped mullites). The
whiskers can be silicate mineral whiskers or whiskers made of one
or more silicate minerals.
[0067] The whiskers present in the material of the present
invention can be or include in-situ whiskers, which, for purposes
of the present invention, refer to the fact that the whiskers are
formed during the formation of the material of the present
invention (e.g., during formation of the composite of the present
invention as a result of reactive sintering). The in-situ whiskers
can have a different morphology from the pre-formed whiskers.
Preferably, the in-situ whiskers can have diameters of from 0.05
micron to about 2 microns (e.g., from 0.05 micron to 2 microns,
0.05 micron to 1.5 microns, 0.05 micron to 1 micron, 0.1 micron to
1 micron, 0.5 micron to 1 micron, 0.75 micron to 1.5 microns). The
in-situ whiskers can have an aspect ratio of from about 10 to about
100 (e.g., from 10 to 75, from 15 to 100, from 20 to 100, from 10
to 45, from 15 to 40, from 20 to 35). The in-situ whiskers have a
length of from about 1 micron to about 50 microns (e.g., from 1
micron to 40 microns, from 1 micron to 30 microns, from 1 micron to
20 microns, from 1 micron to 10 microns, from 1 micron to 5
microns, from 5 microns to 50 microns, from 10 microns to 50
microns, from 15 microns to 50 microns, from 20 microns to 50
microns, from 25 microns to 50 microns, and the like). It is to be
understood that the in-situ whiskers can be a combination of
various diameters, and/or various aspect ratios, and/or various
lengths. It is to be understood that the in-situ whiskers can have
relatively consistent diameters with varying aspect ratios and/or
varying lengths. The in-situ whiskers can have relatively
consistent aspect ratios and varying diameters and/or varying
lengths. The in-situ whiskers can have relatively consistent
lengths and varying diameters and/or varying aspect ratios. With
respect to consistent diameters and/or consistent aspect ratios
and/or consistent lengths, it is to be understood, for purposes of
the present invention, that consistent refers to diameters, aspect
ratios, and/or lengths that are within 25%, or within 10%, or
within 5%, or within 1% of the other diameters and/or other aspect
ratios, and/or other lengths of the in-situ whiskers. The various
ranges for the diameters, aspect ratios, and/or lengths, for
purposes of the present invention, can be considered average
diameters, average aspect ratios, and/or average lengths. As an
option, these ranges can be considered maximum values for the
diameters, and/or aspect ratios, and/or lengths.
[0068] The in-situ whiskers can be present in the material of the
present invention in various amounts. For instance, the
concentration of the in-situ whiskers can be present in an amount
of from 0.1 wt % to 99.9 wt % based on the weight of the material
Preferably, the concentration of the in-situ whiskers is present in
an amount of from about 10 wt % to about 50% (such as from 15% to
45 wt %, 20 wt % to 45 wt %, 30 wt % to 45 wt %, 30 wt % to 40, and
the like), based on the weight of the material.
[0069] The in-situ whiskers can be uniformly distributed throughout
the material (e.g., uniform concentration) of the present
invention. The in-situ whiskers can be considered a continuous
phase or can be considered a whisker phase in the material of the
present invention. The reference to continuous phase is a reference
to in-situ whiskers that can, as an option, be present in such an
amount that the in-situ whiskers contact or touch each other (in
two or three dimensions throughout the material) and, therefore,
form a continuous phase throughout the material of the present
invention. The concentration of the in-situ whiskers can be the
same throughout the material or can be different, such as in the
form of gradients, wherein one region of the material can have a
higher concentration of in-situ whiskers compared to another
region, such as a surface region versus a non-surface region.
[0070] Besides the in-situ whiskers or in lieu of, the material of
the present invention can include pre-formed whiskers, such as
pre-formed mineral-based or metal oxide-based whiskers, such as
mullite whiskers or needle-shaped mullite that is pre-formed. The
pre-formed whiskers can have and preferably have a different
morphology from the in-situ whiskers. For instance, the pre-formed
whiskers can be micro-, sub-micro, or nano-whiskers. The pre-formed
whiskers can be whisker seeds. The pre-formed whiskers can have an
aspect ratio of from 1 to 20, such as 1 to 5. The pre-formed
whiskers can have a length of from 0.01 to 1 micron, such as from
0.01 to 0.75 micron, from 0.1 to 0.875 micron, from 0.1 to 0.5
micron. The pre-formed whiskers can have a diameter of from about
0.01 to 0.5 micron (e.g., from 0.01 to 0.3 micron). The pre-formed
whiskers can be present in the material of the present invention in
an amount of from about 0.001 wt % to 40 wt %, such as from 0.001
wt % to 30 wt %, from 0.001 wt % to 20 wt %, from 0.001 wt % to 10
wt %, from 0.01 wt % to 5 wt % or less based on the weight of the
material of the present invention. The pre-formed whiskers can be
uniformly present throughout the material. The pre-formed whiskers
can be present as a non-continuous phase. The pre-formed whiskers
can be scattered in such a manner that the pre-formed whiskers do
not touch each other or rarely do.
[0071] The in-situ whiskers and/or pre-formed whiskers can be
present in a random manner throughout the matrix or amorphous phase
of the material of the present invention. The whiskers can be
considered to be in a random alignment in the material of the
present invention.
[0072] The material of the present invention can be in the form of
a sphere, where this sphere is solid or hollow, or has one or more
voids present within the sphere. The material can be a sphere or
similar shape, which is hollow in the interior of the sphere. The
sphere can have a smooth, glassy surface that can contribute to an
effective seal against penetration from liquids or gases in the
environment.
[0073] As an option, the material of the present invention can form
a shell around one or more other materials, such as a template or
template material, which can be in the form of a sphere or other
shape and which can be a solid material or a hollow material. For
instance, the material of the present invention can form a shell
around a hollow sphere, such as a cenosphere or other similar
material. When the material of the present invention is present as
a shell and encapsulates one or more other materials, such as a
sphere (like a hollow sphere), the coefficient of thermal expansion
between the shell and the template material can be the same or
within 20% of each other, such as within 10%, within 5%, within 1%,
or within 0.5% of each other.
[0074] As an option, the present invention relates to a particle or
proppant having a template material and shell on the template
material, wherein the shell at least includes or is the material of
the present invention as described herein. The template material
(for instance, a hollow sphere, such as a cenosphere) can have the
same components as the shell from the standpoint of having a matrix
or amorphous phase that has whiskers or a whisker phase present.
For purposes of the present invention, it is to be understood that
the template material can have the same or different composition
and/or characteristics as the shell with respect to the components
present and/or amount of each component. The concentration of the
in-situ and/or pre-formed whiskers in the template can be different
from the concentration of the in-situ and/or pre-formed whiskers in
the shell. For instance, the weight ratio of the concentration of
whiskers present in the shell to the concentration of whiskers in
the template can be a weight ratio of 50:1, 40:1, 30:1, 25:1, 20:1,
15:1, 10:1, 7:1, 5:1, 4:1, 3:1, 2:1, 1.75:1, 1.50:1, 1.25:1
(shell:template), and the like. For instance, the concentration of
the whiskers present in the shell can be the amounts referenced
above for the material of the present invention and the amount of
the whiskers present in the template can be, for instance, from
about 0.1 wt % to 40 wt %, such as from 0.5 wt % to 30 wt %, 0.75
wt % to 20 wt %, 1 wt % to 10 wt %, 1 wt % to 5 wt %, 1 wt % to 3
wt %, wherein this weight is based on the weight of the template
material. The exact composition of the shell compared to the
template material can be the same or different with respect to the
individual components that make up the shell and template.
[0075] For purposes of the present invention, the in-situ whisker
concentration to pre-formed whisker concentration can be a weight
ratio such as from 1000:1, 100:1, 75:1, 50:1, 40:1, 25:1, 10:1,
200:1, 150:1, 100:1, 50:1, 25:1, 10:1, 5:1, 4:1, 3:1, 2:1, 1.75:1,
1.5:1, 1.25:1, 1.1:1, 1:1, 0.9:1, 0.8:1 (in-situ:pre-formed), and
the like, wherein this weight ratio is based on the weight
percentage of in-situ whiskers compared to the weight percent of
pre-formed whiskers present in the material of the present
invention (or in the template).
[0076] The proppant (or sintered body) can have a hollow core or a
solid core, and can have a low specific gravity, for example, a
specific gravity in a range of from about 1.0 g/cc to about 2.5
g/cc, while maintaining a crush strength in a range of from about
500 psi to about 20,000 psi, and/or a flexural strength in a range
of from about 1 MPa to about 200 MPa, or more.
[0077] The proppants of the present invention can provide oil and
gas producers with one or more of the following benefits: improved
flow rates, enhanced hydrocarbon recovery, improved productive life
of wells, improved ability to design hydraulic fractures, and/or
reduced environmental impact. The proppants of the present
invention are designed to improve flow rates, eliminating or
materially reducing the use of permeability destroying polymer
gels, reducing pressure drop through the proppant pack, and/or
reducing the amount of water trapped between proppants thereby
increasing hydrocarbon "flow area." Lower density enhances proppant
transport deep into the formation, increasing the amount of
fracture-area propped, and thereby increasing the mechanical
strength of the reservoir. The low density of the present
invention's proppants can reduce transportation costs. Because the
proppant is lighter, less pumping force is needed, potentially
lowering production costs and reducing damage to the formation.
[0078] Proppants of the present invention preferably enable the use
of simpler completion fluids and less (or slower) destructive
pumping. Formations packed with lower density proppants of the
present invention can exhibit improved mechanical
strength/permeability and thus increased economic life. Enhanced
proppant transport enabled by lower density proppants enable the
emplacement of the proppant of the present invention in areas that
were previously impossible, or at least very difficult to prop. As
a result, the mechanical strength of the subterranean formations
can be improved with reduced decline rates over time.
[0079] If lower density proppants are employed, water and/or brine
solutions can be used in place of more exotic completion fluids.
The use of simpler completion fluids can reduce or eliminate the
need to employ de-crosslinking agents. Further, increased use of
environmentally friendly proppants can reduce the need to employ
other environmentally damaging completion techniques such as
flashing formations with hydrochloric acid. The low density
properties that can be exhibited by the proppants of the present
invention eliminates or greatly reduces the need to employ
permeability destroying polymer gels as the proppants are more
capable of staying in suspension.
[0080] The present invention also relates to low density proppants
that can be utilized, for example, with water and/or brine carrier
solutions.
[0081] The proppant can be either solid throughout or hollow within
the proppant. In the present invention, a solid proppant is defined
as an object that does not contain a void space in the center,
although a porous material would be suitable and is optional; a
fully dense material is not a requirement of solid proppant. A
hollow material is defined as an object that has at least one void
space inside (e.g., generally centrally located within the
proppant) with a defined size and shape.
[0082] The material of the present invention can have isotropic
properties and/or anisotropic properties. In other words, the
ceramic material can have measurable properties that are identical
in all directions (isotropic), but can also have properties that
differ according to the direction of measurement (anisotropic).
[0083] The template preferably can have a diameter in the size
range of, for example, from about 1 nm to about 3000 .mu.m, or from
about 25 .mu.m to about 2000 .mu.m, or from about 80 .mu.m to about
1500 .mu.m, or from about 120 .mu.m to about 300 .mu.m.
[0084] The proppants of the present application can have a specific
gravity of, for example, from about 0.6 g/cc to about 2.5 g/cc. The
specific gravity can be, for example, from about 2.0 g/cc to about
2.5 g/cc, from about 1.0 g/cc to about 2.5 g/cc, from about 1.0
g/cc to about 2.2 g/cc, from about 1.0 g/cc to about 2.0 g/cc, from
about 1.0 g/cc to about 1.8 g/cc, from about 1.0 to about 1.6 g/cc,
or from about 0.8 g/cc to about 1.6 g/cc. Other specific gravities
above and below these ranges can be obtained. The term "specific
gravity" as used herein is the weight in grams per cubic centimeter
(g/cc) of volume, excluding open porosity in determining the
volume. The specific gravity value can be determined by any
suitable method known in the art, such as by liquid (e.g., water or
alcohol) displacement or with an air pycnometer.
[0085] The strength properties of the proppant can be dependent on
the application. The proppant can have a crush strength of at least
1,000 psi. The crush strength can be from about 2,000 psi to about
25,000 psi or higher. The crush strengths can be greater than 9,000
psi, greater than 15,000 psi, or greater than 25,000 psi. Other
crush strengths below or above these ranges are possible. A crush
strength below 3000 psi is an option, such as 500 psi to 3000 psi,
or 1000 psi to 2,000 psi. Crush strength can be measured, for
example, according to American Petroleum Institute Recommended
Practice 60 (RP 60).
[0086] The proppant can have any particle size. For instance, the
proppant can have a particle diameter of from about 1 nm to 1 cm,
from about 1 .mu.m to about 1 mm, from about 10 .mu.m to about 10
mm, from about 100 .mu.m to about 5 mm, from about 50 .mu.m to
about 2 mm, or from about 80 .mu.m to about 1,500 .mu.m. The
optimum size of the proppant can depend on the particular
application.
[0087] The clay or clays used can be in uncalcined, partially
calcined, and/or calcined forms, or any mixtures of such forms. The
term "uncalcined clay" is understood by those of ordinary skill in
the art to mean clay in its natural "as-mined" condition.
Uncalcined clay has not been subjected to any type to treatment
that would result in a chemical or mineralogical change, and can
also be referred to as "raw" clay. The terms "partially calcined
clay" and "calcined clay" are understood by those of ordinary skill
in the art to mean clay that has been subjected to a heat treatment
at times and temperatures, typically about 500.degree. C. to
800.degree. C., to remove some (partially calcined) or
substantially all (calcined) organic material and water of
hydration from the clay.
[0088] In the present invention, the present invention also relates
to a proppant used to prop open subterranean formation fractions
comprising a particle or particles with controlled buoyancy and/or
crush strength. The controlled buoyancy can be a negative buoyancy,
a neutral buoyancy, or a positive buoyancy in the medium chosen for
pumping the proppant to its desired location in the subterranean
formation. The medium chosen for pumping the proppant can be any
desired medium capable of transporting the proppant to its desired
location including, but not limited to a gas and/or liquid,
energized fluid, foam, and aqueous solutions, such as water, brine
solutions, and/or synthetic solutions. Any of the proppants of the
present invention can have a crush strength sufficient for serving
as a proppant to prop open subterranean formation fractures.
[0089] The proppants of the present invention can comprise a single
particle or multiple particles and can be a solid, partially
hollow, or completely hollow in the interior of the particle. The
particle can be spherical, nearly spherical, oblong (or any
combination thereof), or have other shapes suitable for purposes of
being a proppant. The proppant may contain filler in addition to
the whiskers. The filler is a compound that does not reactively
sinter with the ceramic material. Examples of fillers include
graphite, metals (e.g., noble metals), metal oxides (e.g., cerium
oxide) and metal sulfides (e.g., molybdenum disulfide).
[0090] The proppant of the present invention can be a sintered
body, such as a sphere having a Krumbein sphericity of at least
about 0.5 and a roundness of at least about 0.4. The proppant can
include a) a plurality of ceramic whiskers or oxides thereof and b)
a glassy phase and c) optionally at least one crystalline phase,
such as a non-whisker crystalline phase and d) optionally a
plurality of microspheres, wherein the sintered sphere has a
diameter of from about 90 microns to 2,500 microns, and the
sintered sphere has a specific gravity of from 0.8 g/cc to about
3.8 g/cc, and the proppant has a crush strength of from about 1,000
psi or greater.
[0091] The proppants described herein of the present invention can
include one or more of the following characteristics: [0092] 1)
said glassy phase is present in an amount of at least 10% by
weight, based on the weight of the proppant (e.g., at least 15%, at
least 20%, at least 25%, at least 30%, at least 40%, at least 50%,
such as from 15% to 70%, all based on wt %, based on the weight of
the proppant); [0093] 2) said whiskers, such as ceramic whiskers,
have an average length of less than 5 microns (e.g., less than 4
microns, less than 3.5 microns, less than 3.2 microns, less than 3
microns, less than 2.7 microns, less than 2.5 microns, less than
2.2 microns, such as from 0.5 micron to 5 microns, or from 1 micron
to 3.5 microns, or from 0.8 micron to 3.2 microns, or from 1 micron
to 3 microns or from 1.2 to 1.8 microns); [0094] 3) said whiskers,
such as ceramic whiskers, have an average width of less than 0.35
micron (e.g., less than 0.3, less than 0.28, less than 0.25, less
than 0.2, less than 0.15, such as from 0.05 to 0.34 micron, from
0.2 to 0.33 micron, from 0.1 to 0.3 micron, from 0.12 to 0.2
micron, all units in microns); [0095] 4) said whiskers, such as
ceramic whiskers, have a whisker length distribution, d.sub.as, of
about 8 or less (e.g., 7 or less, 6 or less, 5 or less, 4 or less,
3 or less, 2 or less, 1 or less, 0.5 or less, 0.4 or less, 0.3 or
less, 0.2 or less, such as 0.1 to 8, 0.1 to 7, 0.1 to 6, 0.1 to 5,
0.1 to 4, 0.1 to 3, 0.1 to 2, 0.1 to 1, 0.1 to 0.75, 0.1 to 0.5,
0.1 to 0.3, 0.1 to 0.2, 0.1 to 1.8), wherein,
d.sub.as={(d.sub.a90-d.sub.a10)/d.sub.a50} wherein d.sub.a10 is a
whisker length wherein 10% of the whiskers have a smaller length,
d.sub.a50 is a median whisker length wherein 50% of the whiskers
have a smaller whisker length, and d.sub.a90 is a whisker length
wherein 90% of the whiskers have a smaller whisker length; [0096]
5) said proppant having a porosity from about 1% to 70% by weight
where
[0096] porosity ( % ) = 100 - ( SG m SG t ) .times. 100 and
##EQU00001## SG m = measured specific gravity and ##EQU00001.2## SG
t = theoretical specific gravity ; ##EQU00001.3## [0097] 6) said
proppant having a porosity from about 5 wt % to 50 wt % by weight
of proppant; [0098] 7) said proppant having a porosity from about 3
wt % to 20 wt % by weight of proppant; [0099] 8) said proppant
having a porosity from about 4 wt % to 16 wt % by weight of
proppant; [0100] 9) said proppant having a specific gravity of from
1.6 to 1.8 with a crush strength of at least 2000 psi; [0101] 10)
said proppant having a specific gravity of from 1.8 to 2 with a
crush strength of at least 3000 psi; [0102] 11) said proppant
having a specific gravity of from 2 to 2.1 with a crush strength of
at least 5,000 psi; [0103] 12) said proppant having a specific
gravity of from 2.25 to 2.35 with a crush strength of at least
8,000 psi; [0104] 13) said proppant having a specific gravity of
from 2.5 to 3.2 with a crush strength of at least 18,000 psi;
[0105] 14) said proppant having a specific gravity of from 2.5 to
3.2 with a crush strength of at least 25,000 psi; [0106] 15) said
proppant having a combined clay amount and cristobalite amount of
less than 20% by weight of proppant; [0107] 16) said proppant
having a free alpha-alumina content of at least 5% by weight of
said proppant (e.g., 5 wt % to 70 wt % or more, at least 10 wt %,
at least 20 wt %, at least 30 wt %, at least 40 wt %, based on the
weight of the proppant); [0108] 17) said proppant having an HF
etching weight loss of less than 35% by weight of said proppant
(e.g., less than 30% by weight, less than 25% by weight, less than
20% by weight, less than 15% by weight, less than 10% by weight,
such as from 10 wt % to 34 wt %, from 15 wt % to 30 wt %, from 18
wt % to 28 wt % by weight of said proppant); [0109] 18) said
proppant having said microspheres present as hollow glass
microspheres having a particle size distribution, d.sub.as, of from
about 0.5 to about 2.7 (e.g., 0.5 to 2.6, 0.8 to 2.2, 1 to 2, 0.5
to 2, 0.5 to. 1.5, 0.5 to 1), wherein,
d.sub.as={(d.sub.a90-d.sub.a10)/d.sub.a50} wherein d.sub.a10 is a
particle size wherein 10% (by volume) of the particles have a
smaller particle size, d.sub.a50 is a median particle size wherein
50% (by volume) of the particles have a smaller particle size, and
d.sub.a90 is a particle size wherein 90% (by volume) of the
particle volume has a smaller particle size; [0110] 19) said
proppant having microspheres present wherein said microspheres are
uniformly present in said proppant or in a layered region of said
proppant; [0111] 20) said whiskers, such as ceramic whiskers, are
present in an amount of from 5% to 60% by weight of said proppant
(e.g., from 5% to 50%, from 5% to 45%, from 5% to 40%, from 5% to
35%, from 5% to 30%, from 5% to 25%, from 5% to 20%, from 5% to
15%, from 10% to 25%, from 15% to 25%, all by wt % based on the
weight of said proppant); [0112] 21) said proppant has a combined
clay amount and cristobalite amount of less than 20% (e.g., less
15%, less than 10%, less than 5%, less than 1%, such as from 0.1%
to 3%, all wt %) by weight of proppant and/or said whiskers, such
as mullite whiskers, are present in an amount of 60% or more by
weight of said proppant (e.g., from 5% to 50%, from 5% to 45%, from
5% to 40%, from 5% to 35%, from 5% to 30%, from 5% to 25%, from 5%
to 20%, from 5% to 15%, from 10% to 25%, from 15% to 25%, all by wt
% based on the weight of said proppant); [0113] 22) said proppant
has a high whisker distribution density based on individual
whiskers present in the proppant (# of whiskers per mg of
proppant); [0114] 23) said proppant has a unimodal whisker
distribution; [0115] 24) said proppant has at least two layers that
form a laminate structure (such as three layers or four layers or
five layers); [0116] 25) said proppant has at least a first layer
and a second layer that form a laminate structure wherein the
average length of said whiskers in said first layer compared to
said second layer is different; [0117] 26) said proppant has at
least a first layer and a second layer that form a laminate
structure wherein the average width of said whiskers in said first
layer compared to said second layer is different; [0118] 27) said
proppant has a smooth surface comprised of both crystalline and
amorphous materials. [0119] 28) said whiskers in said proppant are
less euhedral and more anhedral; [0120] 29) said proppant has at
least one region (e.g., one circumference or radial region closer
to the outer surface) of first whiskers and at least one region
(e.g., one circumference or radial region further away from the
outer surface of the proppant) of second whiskers, wherein the
average whisker length for the first and second whiskers is
different by at least 10% (e.g., at least 15%, at least 20%, at
least 25%, at least 30%, at least 35%, at least 40%, at least 45%,
at least 50%, at least 55%, at least 60%, at least 70%, at least
80%, at least 90%, at least 100%, at least 120%, at least 140, at
least 200% different). Where R is the radius of the proppant and
R=0 is the center of the proppant, and R=100 is the outer surface
of the proppant, an R from 1 to 50 (e.g., from 5 to 50, from 10 to
40, from 10 to 25, from 10 to 20) can have an average whisker
length that is larger than a region where R is greater (an outer
region). These regions can be all interior to a shell region if
present, or one of the regions can be part of a shell region and
the other region can be part of a template or core region that is
encapsulated by a shell(s). [0121] 30) said proppant has at least
one radial region of first whiskers and at least one region of
second whiskers, wherein the average whisker width is different by
at least 10% (e.g., at least 15%, at least 20%, at least 25%, at
least 30%, at least 35%, at least 40%, at least 45%, at least 50%,
at least 55%, at least 60%, at least 70%, at least 80%, at least
90%, at least 100%, at least 120%, at least 140, at least 200%
different). Where R is the radius of the proppant and R=0 is the
center of the proppant, and R=100 is the outer surface of the
proppant, an R from 1 to 50 (e.g., from 5 to 50, from 10 to 40,
from 10 to 25, from 10 to 20) can have an average whisker width
that is larger than a region where R is greater (an outer region).
[0122] 31) said proppant has a major phase of whiskers of less than
one micron and a secondary minor phase of whiskers of one micron or
higher; and/or [0123] 32) said whiskers, such as ceramic whiskers,
have a whisker length distribution having d.sub.a90, which is a
whisker length wherein 90% of the whiskers have a smaller whisker
length, of less than 12 microns (e.g., less than 10 microns, less
than 8 microns, less than 7 microns, less than 6 microns, less than
5 microns, less than 4 microns, less than 3 microns, less than 2
microns, such as from 1 to 10, 1.5 to 5, 1.7 to 5, 1.8 to 4, 1.9 to
3.5, 1.5 to 3.5).
[0124] It is to be understood that all averages and distributions
mentioned above or herein are based on measuring at least 50
whiskers picked on a random basis in a proppant. Preferably, at
least 10 proppants are measured in this manner and an average
obtained.
[0125] In the present invention, the one or more of said
characteristics mentioned above can provide stress reducing
properties on said proppant compared to the same proppant but
without said characteristics. The proppant can have an alumina
content of at least 35% by weight of said proppant, such as at
least 40%, at least 45%, at least 50%, at least 55%, at least 60%,
such as from 35% to 55%, all wt % based on the weight of the
proppant. The proppant can have mullite whiskers, such as present
in an amount of from 10 wt % to 40 wt % by weight of said proppant
(e.g., 15 wt % to 30 wt %, or 20 wt % to 25 wt % and the like). The
proppant can include quartz. The proppant can have quartz in an
amount of from 0.1 wt % to 1 wt % based on the weight of the
proppant. The proppant can have at least one layered shell
encapsulating a hollow spherical template. The proppant can have at
least one layered shell encapsulating a hollow spherical template,
and said microspheres (e.g., in-situ formed and/or pre-formed) are
present in said at least layered shell.
[0126] The present invention also relates to a method of preparing
a proppant that employs reactive or reaction sintering to form a
unique microstructure, in which anisotropic crystals (such as
whiskers, needles, leaves, or fibers) are formed in-situ through
the chemical reactions of the raw or starting materials. The raw
materials can comprise ceramic precursors, for example, talc, clay,
alumina, silica, kyanite, or any combination thereof. The reactive
sintering process can produce a ceramic proppant having randomly
aligned whiskers that can be formed in-situ and/or introduced
through one or more of the starting materials. The method can
produce a ceramic proppant comprising anisotropic crystals. The
flexural strength of such a proppant can have, for example, at
least 50% more strength than a proppant with isotropic structure
that can be formed by sintering pre-formed materials, at the same
or about the same specific gravity. The reactive or reaction
sintering can form substantially spherical microspheres or pores
with a smooth glassy interior wall inside the amorphous phase by
controlled release of gaseous materials, such as water, from the at
least one amorphous material that contains an entrapped vaporizable
material such as water. The reactive or reaction sintering process
in the presence of the amorphous material that contains an
entrapped vaporizable material such as water, promotes a smooth
outer surface on the proppant. The amorphous material that contains
an entrapped vaporizable material, such as water, can comprise
perlite, stober silica, pumice, andesite, scoria, volcanic glasses
or any combinations thereof.
[0127] In the present invention, the ceramic particles or any type
of proppant particle can benefit from using membrane separation
processes for one or more of the starting materials that are used
to form the ceramic particles or any type of proppant. The membrane
separation processes can be also useful in the final product as
well.
[0128] The starting material(s) particle size and its distribution
can be strictly controlled by membrane separation processes. The
selected incoming raw materials can be dispersed into a slurry,
such as an aqueous slurry like water. At least one dispersant can
be used as well for improving the dispersion of the slurry. The
slurry can be milled, such as through an attrition mill, ball mill,
jet mill, hammer mill or any combination thereof. After milling or
otherwise obtaining the desired general particle size, the slurry
can be diluted to a desirable concentration, then feed into at
least one membrane filtration device. By such a process, the larger
particles are left in the filtration cake or in the retained slurry
while the smaller particles remain in the effluent slurry. With
such a process, the larger particles are filtered out. The effluent
slurry can be then feed in to a second membrane filter with a
smaller pore size. Going through the same process as described
above, the filtration cake or the retained slurry having a narrow
particle size distribution of raw materials is obtained.
Essentially this membrane process permits a very accurate and
controlled way to obtain a "cut" of desirable particle sizes,
whereby the unwanted smaller particles and the unwanted larger
particles are removed.
[0129] In the present invention, one can use the above membrane
filtration process to separate particles size into various groups,
such as with an average particle size of 0.2 micron, 0.5 micron, 1
micron, 1.5 micron, and 2.0 microns, and so on, depending on the
membrane pore size. The width of the size distribution can be
determined by the two "cuts" of membrane sizes. In general, a much
narrower size distribution is desirable for product performance and
this process permits such a distribution. In addition to membrane
filtration, air classification can be employed alone or in
combination with membrane separation to produce the desired mean
particle size and/or size distribution.
[0130] As an example, raw material particles with the same particle
size distributions can be mixed, and then spray coated to form
ceramic green spheres, or granulated in a granulator. Due to the
same particle sizes, particle packing is well controlled. Pores
between particles can be well preserved. During the firing process,
particles sinter together, and the porosity can be well preserved
after the firing process, with a narrow pore size distribution. By
controlling the particle size with the narrow distribution, a pore
size can be well controlled after the sintering process. Narrow
pore size distribution can be achieved, so that an adequate amount
of porosity can be added in to the ceramics, while most of
mechanical strength can be preserved.
[0131] As a further example, two different size cuts of raw
materials can be mixed together (e.g., 2 micron particles mixed
with 0.5 micron particles and 0.2 micron particles), going through
the forming processes described above. After forming, the green
body can be subjected to firing at a high temperature, and a near
zero porosity containing proppant can be produced.
[0132] In the present invention, two types of a membrane separation
device can be used (e.g., a "dead end filtration" and another type
is cross flow membrane separation.) The former one can handle a
relatively high concentration of slurry, which yield a broader
particle size distribution. The later gives very narrow and clean
cut particles size distribution.
[0133] In the present invention, size control of the raw or
starting material, provide the possibility of precise sintering
under well controlled firing cycles. So the grain size growth can
be controlled, and high strength materials with uniform small grain
size materials can be produced under the same specific gravity.
[0134] In the present invention, the number of pores and/or pore
size can be well controlled, so an adequate amount of porosity can
be added into a ceramic proppant, while loss of mechanical strength
can be minimized. Therefore, high strength/low specific gravity
proppant can be produced. Formation of pores can be enhanced by the
addition of an amorphous material that contains an entrapped
vaporizable material such as water and releasing the vaporizable
material in a controlled rate.
[0135] As an option, in the present invention, the various average
particle sizes and/or particle size distributions are the same or
about the same with respect to each of the starting materials that
form the green body. When the particle sizes of one or more, and,
preferably all of the starting materials that can have particle
sizes, are about the same or the same, the formation of the green
body by mixing the various starting materials together can be more
uniform and the distribution of the different starting materials
gets distributed throughout the green body in a more uniform way,
such that the overall green body and the resulting sintered body,
such as the proppant, has a uniform distribution of each of the
starting materials, thereby forming a very consistent sintered body
having consistent properties throughout the sintered body or
selected parts or regions thereof, and thereby reducing the chances
of a flaw or defect existing in the sintered body. The average
particle size and/or distribution of two or more of the starting
materials can be within +/-20% of each other, +/-15% of each other,
+/-10% of each other, +/-7% of each other, +/-5% of each other,
+/-4% of each other, +/-3% of each other, +/-2% of each other,
+/-1% of each other, +/-0.75% of each other, +/-0.5% of each other,
+/-0.25% of each other, +/-0.1% of each other, +/-0.05% of each
other, or +/-0.01% of each other.
[0136] As a result of such techniques, such as the membrane
filtration device, the particle size distribution for any of the
starting materials, such as the ceramic or ceramic precursor, the
microsphere former, metal oxide, metals, (or, for that matter, any
particulate starting material) and the like can have a particle
distribution that is very tight, such that the particle size
distribution as defined herein (d=[(D.sub.90-D.sub.10)/D.sub.50],
wherein d is 0.4 to 1, such as 0.05 to 0.9, 0.07 to 0.5, 0.09 to
0.4, and the like.
[0137] The expression "reactive sintering" as used herein, can
include a process wherein heat is applied to a composition, causing
that composition to undergo, at least in part, a chemical reaction
forming a new composition. The composition is heated to below or
about its melting point.
[0138] The term "green body" or "green pellet" refers to
pre-sintered material of this invention that has been shaped from
the disclosed compositions but are not sintered. The mixing step
typically provides an aqueous dispersion or paste, which is later
dried.
[0139] Drying can be performed at a temperature in the range of
from about 30.degree. C. to 600.degree. C., such as from about
120.degree. C. to 150.degree. C., and can occur over a period of up
to about 48 hours, depending on the drying technique employed. Any
type of dryer customarily used in the industry to dry slurries and
pastes can be used. Drying can be performed in a batch process
using, for example, a stationary dish or container. Alternatively,
drying can be performed in a spray dryer, fluid bed dryer, rotary
dryer, rotating tray dryer or flash dryer. The pellets can be
screened to provide a suitable median particle size, preferably
after drying. For example, a top screen having a mesh size of about
10 or 11 mesh can be used to screen out the largest particles and a
bottom screen having a mesh size of about 18 or 20 can be used to
remove the finer particles. The choice of top and bottom screens
depends, in part, on the mixture produced and can be adjusted to
tailor the median particle size of the mixture. A further screening
may take place after sintering. The slurry containing the green
body material to form the green body can be sprayed or otherwise
applied to a hot plate(s) (horizontal or inclined surface). The hot
plate can have a metal or ceramic surface. A burner or a series of
burners are located under the plate to provide heat to the hot
plate surface. The surface is maintained above the evaporation
temperature of the solvent (e.g., water) and preferably a lot
higher (e.g., at least 10% higher or at least 30% or at least 50%
higher in temperature). The droplet sizes are bigger in size than
the desired dried size. For instance, the droplet size can be at
least 10% larger, at least 50%, at least 100% larger than the final
granule size that forms after evaporation occurs. The
process/device described in U.S. Pat. No. 5,897,838 (incorporated
in its entirety by reference herein) can be adopted as well for
this purpose.
[0140] The template material can be porous, non-porous, or
substantially non-porous. For purposes of the present invention, a
substantially non-porous material is a material that is preferably
at least 80 vol % non-porous in its entirety, more preferably, at
least 90 vol % non-porous. The template material can be a hollow
sphere or it can be a closed foam network, and/or can be a
non-composite material. A non-composite material, for purposes of
the present invention, is a material that is not a collection of
particles which are bound together by some binder or other adhesive
mechanism. The template material of the present invention can be a
single particle. The template material can be a cenosphere or a
synthetic microsphere such as one produced from a blowing process
or a drop tower process.
[0141] The template material can have a crush strength of 5000 psi
or less, 3000 psi or less, or 1000 psi or less. In the alternative,
the template material can have a high crush strength such as 1000
psi or more, or from about 3000 psi to 10,000 psi. For purposes of
the present invention, crush strength can be determined according
to API Practice 60 (2.sup.nd Ed. December 1995). A template
material having a low crush strength can be used to provide a means
for a coating to be applied in order to form a shell wherein the
shell can contribute a majority, if not a high majority, of the
crush strength of the overall proppant.
[0142] The proppant can be spherical, oblong, nearly spherical, or
any other shapes. For instance, the proppant can be spherical and
have a Krumbein sphericity of at least about 0.5, at least 0.6, at
least 0.7, at least 0.8, or at least 0.9, and/or a roundness of at
least about 0.4, at least 0.5, at least 0.6, at least 0.7, or at
least 0.9. The term "spherical" refers to sphericity and roundness
on the Krumbein and Sloss Chart by visually grading 10 to 20
randomly selected particles.
[0143] In accordance with the method of the present invention, the
ceramic proppant produced as described above may be used as
proppants, gravel or fluid loss agents in hydraulic fracturing
and/or frac packing. As stated above, the present invention also
relates to a proppant formulation comprising one or more proppants
of the present invention with a carrier. The carrier can be a
liquid or gas or both. The carrier can be, for example, water,
brine, hydrocarbons, oil, crude oil, gel, foam, or any combination
thereof. The weight ratio of carrier to proppant can be from
10,000:1 to 1:10,000, or any ratio in between, and preferably about
0.1 g proppant/liter fluid to 1 kg proppant/liter fluid.
[0144] The present invention, as one example, relates to a method
for producing the material of the present invention as stated
herein. The starting components used in the methods described
herein can be the same components or precursors of the same
components mentioned earlier.
[0145] The present invention also relates to a method to make
strong, tough, and/or lightweight glass-ceramic matrix composites
through a self-toughening structure generated by viscous reaction
sintering of a complex mixture of oxides. For purposes of this
invention, glass-ceramic composite can be a material in which glass
can comprise from about 0.01% by weight to about 99.9% by weight,
based on the weight of the composite. The typical composition of
the starting mixture can include the following oxides and/or their
precursors in one form or another: Al.sub.2O.sub.3, SiO.sub.2,
Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, K.sub.2O, CaO, Na.sub.2O,
TiO.sub.2, and MgO.
[0146] The method can include forming a green body. The green body
can be formed from a green body material that includes: [0147] i.
at least one metal oxide(s) (and preferably at least two different
metal oxides, a first metal oxide and a second metal oxide that is
different from the first metal oxide) that is preferably capable of
forming whiskers in-situ. The metal oxide can be an aluminum oxide
and/or an aluminum bearing mineral (or ore) and/or a silicon oxide
or a silicon bearing mineral (or ore) or precursors thereof, and
[0148] ii. at least one amorphous material containing at least one
entrapped vaporizable material such as water, and [0149] iii.
pre-formed whiskers (e.g., ceramic or metal oxide or mineral based
whiskers), and [0150] iv. at least one whisker promoter, preferably
in the absence of halide or halide compounds, or preferably in the
absence of fluorine or fluorine compounds.
[0151] The green body is then subjected to sintering under
sintering conditions to form in-situ the material of the present
invention (e.g., a composite having at least one whisker phase and
at least one amorphous phase and optionally, at least one
crystalline particulate phase).
[0152] The at least one metal oxide or precursor thereof can have
any particle size distribution. For example, the particle size
distribution, d.sub.as, can be from about 0.5 to about 15, wherein,
d.sub.as{(d.sub.a90-d.sub.a10)/d.sub.a50} wherein d.sub.a10 is a
particle size wherein 10% (by volume) of the particles have a
smaller particle size, d.sub.a50 is a median particle size wherein
50% (by volume) of the particles have a smaller particle size, and
d.sub.a90 is a particle size wherein 90% (by volume) of the
particle volume has a smaller particle size. The d.sub.as can be
from 0.5 to 15, 0.75 to 15, 1 to 15, 1 to 5, 1 to 6, 1 to 8, 5 to
15, 0.5 to 10, 0.5 to 5, and the like. The metal oxide(s) or metal
oxide precursor can have a median particle size, d.sub.a50, of from
about 0.01 .mu.m to about 100 .mu.m, wherein d.sub.50 is a median
particle size where 50% (by volume) of the particles of the
distribution have a smaller particle size. The median particle
size, d.sub.50, can be from about 1 .mu.m to about 5 .mu.m, from 1
to 5 .mu.m, 1 to 90 .mu.m, 1 to 80 .mu.m, 1 to 70 .mu.m, 1 to 60
.mu.m, 1 to 50 .mu.m, 1 to 40 .mu.m, 1 to 30 .mu.m, 1 to 20 .mu.m,
1 to 10 .mu.m, 10 to 90 .mu.m, 20 to 80 .mu.m, 30 to 70 .mu.m, and
the like, wherein d.sub.a50 is a median particle size where 50% (by
volume) of the particles of the distribution have a smaller
particle size.
[0153] When preferably two different metal oxides (or precursor
thereof) are used, the second metal oxide (or precursor thereof)
can have any particle size, such as a particle size distribution,
The d.sub.as can be from 0.5 to 15, 0.75 to 15, 1 to 15, 1 to 5, 1
to 6, 1 to 8, 5 to 15, 0.5 to 10, 0.5 to 5d.sub.ss, of from about
0.5 to about 15, wherein,
d.sub.ss={(d.sub.s90-d.sub.s10)/d.sub.s50} wherein d.sub.s10 is a
particle size wherein 10% (by volume) of the particles have a
smaller particle size, d.sub.s50 is a median particle size wherein
50% (by volume) of the particles have a smaller particle size, and
d.sub.s90 is a particle size wherein 90% (by volume) of the
particle volume has a smaller particle size. The d.sub.as can be
from 0.5 to 15, 0.75 to 15, 1 to 15, 1 to 5, 1 to 6, 1 to 8, 5 to
15, 0.5 to 10, 0.5 to 5 and the like. The second metal oxide (or
precursor thereof) can have a median particle size, d.sub.a50, of
from about 0.01 .mu.m to about 100 .mu.m, wherein d.sub.a50 is a
median particle size where 50% (by volume) of the particles of the
distribution have a smaller particle size. The median particle
size, d.sub.a50, can be from about 1 .mu.m to about 5 .mu.m, from 1
to 5 .mu.m, 1 to 90 .mu.m, 1 to 80 .mu.m, 1 to 70 .mu.m, 1 to 60
.mu.m, 1 to 50 .mu.m, 1 to 40 .mu.m, 1 to 30 .mu.m, 1 to 20 .mu.m,
1 to 10 .mu.m, 10 to 90 .mu.m, 20 to 80 .mu.m, 30 to 70 .mu.m, and
the like, wherein d.sub.a50 is a median particle size where 50% (by
volume) of the particles of the distribution have a smaller
particle size.
[0154] As an option, the particle size distribution and/or the
median particle size of the first metal oxide or precursor thereof
and the second metal oxide or precursor thereof can be the same or
different, or can be within 1%, 5%, 10%, 15%, 20%, 25% of each
other.
[0155] The at least one amorphous material containing at least one
entrapped vaporizable material such as water can have any particle
size distribution. For example, the particle size distribution,
d.sub.as, can be from about 0.5 to about 15, wherein,
d.sub.as={(d.sub.a90-d.sub.a50} wherein d.sub.a10 is a particle
size wherein 10% (by volume) of the particles have a smaller
particle size, d.sub.a50 is a median particle size wherein 50% (by
volume) of the particles have a smaller particle size, and
d.sub.a90 is a particle size wherein 90% (by volume) of the
particle volume has a smaller particle size. The d.sub.as can be
from 0.5 to 15, 0.75 to 15, 1 to 15, 1 to 5, 1 to 6, 1 to 8, 5 to
15, 0.5 to 10, 0.5 to 5, and the like. The at least one amorphous
material containing at least one entrapped vaporizable material
such as water can have a median particle size, d.sub.a50, of from
about 0.01 .mu.m to about 100 .mu.m, wherein d.sub.a50 is a median
particle size where 50% (by volume) of the particles of the
distribution have a smaller particle size. The median particle
size, d.sub.a50, can be from about 1 .mu.m to about 5 .mu.m, from 1
to 5 .mu.m, 1 to 90 .mu.m, 1 to 80 .mu.m, 1 to 70 .mu.m, 1 to 60
.mu.m, 1 to 50 .mu.m, 1 to 40 .mu.m, 1 to 30 .mu.m, 1 to 20 .mu.m,
1 to 10 .mu.m, 10 to 90 .mu.m, 20 to 80 .mu.m, 30 to 70 .mu.m, and
the like, wherein d.sub.50) is a median particle size where 50% (by
volume) of the particles of the distribution have a smaller
particle size.
[0156] The ratio for forming the in-situ formed whiskers in the
composite can be from about (20 wt % first metal oxide or
precursor/80 wt % second metal oxide(s) or metal oxide precursor)
to about (60 wt % first metal oxide or precursor/40 wt % second
metal oxide(s) or metal oxide precursor).
[0157] The pre-formed whiskers (or pre-formed whisker seeds) can be
present in an amount of from 0.01 wt % to 40 wt %, such as from
about 2% by weight to about 25% by weight, of the green body
material. The inventors have unexpectedly found that whiskers, such
as mullite whiskers, incorporated into the green body material acts
as whisker formation seeds allowing early onset of whisker
formation and at temperatures near the bottom of the range
typically required for formation of mullite whiskers. If sintering
temperature reaches temperatures of about 1500.degree. C., the
conversion of alumina or alumina precursor and siliceous material
to glass is nearly complete and an effective composite is not
formed. In addition, higher temperatures tend to form pores in the
amorphous phase lowering the strength and toughness of the
resulting glass-ceramic material. Mullite whiskers can be naturally
occurring in cenospheres and can be present in an amount of from
about 2% by weight to about 40% by weight of the cenospheres. In
addition or alternatively, small mullite whiskers directly formed
or ground can be added to the green body material, for instance, in
an amount of from about 0.5% by weight to about 2% by weight of the
green body material.
[0158] The whisker promoter can be B.sub.2O.sub.3 and/or one or
more transition metal oxides. Examples include, but are not limited
to, Fe.sub.2O.sub.3, TiO.sub.2, CoO, NiO or any combinations
thereof. The whisker promoter can be used in any amount, for
instance from about 0.1 wt % to 5 wt %, or from about 1% by weight
to about 2% by weight of the green body material or mixture. A
further novel aspect of the present invention is the use of
B.sub.2O.sub.3 and/or transition metal oxide whisker promoters that
can include Fe.sub.2O.sub.3, TiO.sub.2, CoO, and/or NiO or any
combinations thereof, to control the growth of whiskers, such as
mullite whiskers. Materials that promote the formation of mullite
whiskers are typically compounds that include fluorine. U.S. Pat.
No. 4,911,902 mentions the use of SiF.sub.4 in an anhydrous
environment to produce bar-like topaz as a precursor to form
mullite whiskers. L. B. Kong, et al (L. B, Kong. "Effect of
transition metal oxides on mullite whisker formation from
mechanochemically activated powders," Material Science and
Engineering A359 (2003): 75-81, Print.) stated that the addition of
transition metal oxides have shown significant influence on the
mullite formation temperature and the morphology of the mullite
whiskers from the oxide mixtures activated by a high-energy ball
milling process. The inventors have unexpectedly found that various
transition metal oxides and combinations thereof produce a balance
of mullite whiskers and amorphous alumina and silica in a
glass-ceramic composite. The transition metal oxides in the present
invention can include Fe.sub.2O.sub.3, TiO.sub.2, CoO, and/or NiO,
or combinations thereof. Furthermore, the inventors have
unexpectedly discovered that trace amounts of Fe.sub.2O.sub.3 and
other iron oxide compounds present in cenospheres and fly ash can
effectively act as the transition metal oxide promoter.
[0159] The inventors have also found that in-situ mullite whiskers
in the final product can form when a siliceous material that
contains mullite, such as a cenosphere, is saturated with amorphous
silica and alumina. After sintering, a phase separation within the
amorphous phase of the siliceous material occurs resulting in an
amorphous phase deficient in silica and alumina and a crystalline
mullite whisker phase. During phase separation, some of the
amorphous alumina in the amorphous phase can crystallize and
enhance the strength of the resulting composite.
[0160] The inventors have also found that a whisker phase, such as
a mullite whisker phase, can be formed without production of
in-situ mullite. The reactive sintering process effectively can
form an amorphous phase and a mullite phase from mullite that
existed in the starting green body materials.
[0161] Whiskers, such as mullite whiskers, can be present as a
result of both reactive sintering and/or whiskers present in the
starting green body material.
[0162] For exemplary purposes, the following example is provided.
Materials other than those mentioned below can be used.
[0163] The present invention, as one example, relates to a method
for producing a glass-ceramic composite. The method includes the
steps of forming a green body. The green body can be formed from a
green body material that includes: [0164] i. (a) alumina and/or at
least one alumina precursor, and (b) a siliceous material; [0165]
ii. at least one amorphous material containing at least one
entrapped vaporizable material such as water, where [0166] alumina
and silica present in the alumina and/or at least one alumina
precursor, and/or siliceous material and/or the at least one
amorphous material are present in a weight ratio such that
whiskers, such as mullite whiskers, form in said glass-ceramic
composite upon sintering, and [0167] iii. pre-formed mullite
whiskers (e.g., a minor amount), and [0168] iv. at least one
whisker promoter, preferably in the absence of fluorine or fluorine
compounds.
[0169] The green body is then subjected to sintering under
sintering conditions to form a glass-ceramic composite having at
least one whisker phase, such as a mullite whisker phase, and at
least one amorphous phase.
[0170] The alumina precursor can be or include aluminum hydroxide,
bauxite, gibbsite, boehmite or diaspore or any combination thereof.
The alumina or alumina precursor can have any particle size
distribution. For example, the particle size distribution,
d.sub.as, can be from about 0.5 to about 15, wherein,
d.sub.as={(d.sub.a90-d.sub.a10)/d.sub.a50} wherein d.sub.a10 is a
particle size wherein 10% (by volume) of the particles have a
smaller particle size, d.sub.a50 is a median particle size wherein
50% (by volume) of the particles have a smaller particle size, and
d.sub.a90 is a particle size wherein 90% (by volume) of the
particle volume has a smaller particle size. The d.sub.as can be
from 0.5 to 15, 0.75 to 15, 1 to 15, 1 to 5, 1 to 6, 1 to 8, 5 to
15, 0.5 to 10, 0.5 to 5, and the like. The alumina or alumina
precursor can have a median particle size, d.sub.a50, of from about
0.01 .mu.m to about 100 .mu.m, wherein d.sub.a50 is a median
particle size where 50% (by volume) of the particles of the
distribution have a smaller particle size. The median particle
size, d.sub.a50, can be from about 1 .mu.m to about 5 .mu.m, from 1
to 5 .mu.m, 1 to 90 .mu.m, 1 to 80 .mu.m, 1 to 70 .mu.m, 1 to 60
.mu.m, 1 to 50 .mu.m, 1 to 40 .mu.m, 1 to 30 .mu.m, 1 to 20 .mu.m,
1 to 10 .mu.m, 10 to 90 .mu.m, 20 to 80 .mu.m, 30 to 70 .mu.m, and
the like, wherein d.sub.a50 is a median particle size where 50% (by
volume) of the particles of the distribution have a smaller
particle size.
[0171] The siliceous material is any silicon containing material,
such as silicate containing material, silicon containing minerals
or ore, silicates, silicon oxides, and the like. The siliceous
material can be or include one or more cenospheres, fly ash or any
combination thereof. The siliceous material can be natural,
synthetic, or a by-product. The siliceous material can be or
include silicate materials, quartz, feldspar, zeolites, bauxite,
calcined clays or any combination thereof. The siliceous material
can have any particle size, such as a particle size distribution,
The d.sub.as can be from 0.5 to 15, 0.75 to 15, 1 to 15, 1 to 5, 1
to 6, 1 to 8, 5 to 15, 0.5 to 10, 0.5 to 5d.sub.ss, of from about
0.5 to about 15, wherein, d.sub.ss={(d.sub.s90-d.sub.s50} wherein
d.sub.s10 is a particle size wherein 10% (by volume) of the
particles have a smaller particle size, d.sub.s50 is a median
particle size wherein 50% (by volume) of the particles have a
smaller particle size, and d.sub.s90 is a particle size wherein 90%
(by volume) of the particle volume has a smaller particle size. The
d.sub.as can be from 0.5 to 15, 0.75 to 15, 1 to 15, 1 to 5, 1 to
6, 1 to 8, 5 to 15, 0.5 to 10, 0.5 to 5 and the like. The siliceous
material can have a median particle size, d.sub.a50, of from about
0.01 .mu.m to about 100 .mu.m, wherein d.sub.a50 is a median
particle size where 50% (by volume) of the particles of the
distribution have a smaller particle size. The median particle
size, d.sub.a50, can be from about 1 .mu.m to about 5 .mu.m, from 1
to 5 .mu.m, 1 to 90 .mu.m, 1 to 80 .mu.m, 1 to 70 .mu.m, 1 to 60
.mu.m, 1 to 50 .mu.m, 1 to 40 .mu.m, 1 to 30 .mu.m, 1 to 20 .mu.m,
1 to 10 .mu.m, 10 to 90 .mu.m, 20 to 80 .mu.m, 30 to 70 .mu.m, and
the like, wherein d.sub.a50 is a median particle size where 50% (by
volume) of the particles of the distribution have a smaller
particle size.
[0172] The amorphous material and/or other material that can
contain at least one entrapped vaporizable material can be perlite,
stober silica, any amorphous volcanic rock containing silica,
alumina, and the like. The amorphous material can have any particle
size and/or any particle size distribution. The d.sub.as can be
from 0.5 to 15, 0.75 to 15, 1 to 15, 1 to 5, 1 to 6, 1 to 8, 5 to
15, 0.5 to 10, 0.5 to 5. The d.sub.ss can be from about 0.5 to
about 15, wherein, d.sub.ss={(d.sub.s90-d.sub.s10)/d.sub.s50}
wherein d.sub.s10 is a particle size wherein 10% (by volume) of the
particles have a smaller particle size, d.sub.s50 is a median
particle size wherein 50% (by volume) of the particles have a
smaller particle size, and d.sub.s90 is a particle size wherein 90%
(by volume) of the particle volume has a smaller particle size. The
d.sub.as can be from 0.5 to 15, 0.75 to 15, 1 to 15, 1 to 5, 1 to
6, 1 to 8, 5 to 15, 0.5 to 10, 0.5 to 5 and the like. The at least
one amorphous material containing at least one entrapped
vaporizable material, such as water, can have a median particle
size, d.sub.a50, of from about 0.01 .mu.m to about 100 .mu.m,
wherein d.sub.a50 is a median particle size where 50% (by volume)
of the particles of the distribution have a smaller particle size.
The median particle size, d.sub.a50, can be from about 1 .mu.m to
about 5 .mu.m, from 1 to 5 .mu.m, 1 to 90 .mu.m, 1 to 80 .mu.m, 1
to 70 .mu.m, 1 to 60 .mu.m, 1 to 50 .mu.m, 1 to 40 .mu.m, 1 to 30
.mu.m, 1 to 20 .mu.m, 1 to 10 .mu.m, 10 to 90 .mu.m, 20 to 80
.mu.m, 30 to 70 .mu.m, and the like, wherein d.sub.a50 is a median
particle size where 50% (by volume) of the particles of the
distribution have a smaller particle size.
[0173] As an option, the particle size distribution and/or the
median particle size of the alumina or precursor thereof, the
siliceous material, and the at least one amorphous material
containing at least one entrapped vaporizable material can be the
same or different, or can be within 1%, 5%, 10%, 15%, 20%, 25% of
each other.
[0174] The ratio for forming in-situ formed mullite whiskers in the
glass-ceramic composite can be from about (20 wt % siliceous
material/80 wt % alumina or alumina precursor) to about (60 wt %
siliceous material/40 wt % alumina or alumina precursor), wherein
the wt % of siliceous material is based on SiO.sub.2 amount and the
alumina/alumina precursor is based on alumina amount. The ratio is
calculated using the total weight of siliceous material and alumina
present collectively in the alumina or precursor thereof, the
siliceous material, and the at least one amorphous material
containing at least one entrapped vaporizable material.
[0175] The pre-formed whiskers can be obtained from cenospheres
themselves. The pre-formed whiskers can be present in an amount of
from 0.01 wt % to 40 wt %, such as from about 2% by weight to about
25% by weight, of the cenospheres. Thus, if cenospheres are used in
part or entirely as the siliceous material, the cenospheres can
serve a dual purpose, namely as the siliceous source and as the
pre-formed whisker source for purposes of the method. The
pre-formed mullite whiskers can be present in an amount of from
about 0.5% by weight to about 20% by weight of said green body
material.
[0176] The whisker promoter can be one or more transition metal
oxides. Examples include, but are not limited to, B.sub.2O.sub.3,
Fe.sub.2O.sub.3, TiO.sub.2, CoO, NiO or any combinations thereof.
The whisker promoter can be used in any amount, for instance from
about 0.1 wt % to 5 wt %, or from about 1% by weight to about 2% by
weight of the green body material or mixture.
[0177] In general, for the methods of the present invention, the
green body material can include at least one sintering promoter,
such as a sintering aid, a glassy phase formation agent, a grain
growth inhibitor, a ceramic strengthening agent, a crystallization
control agent, or phase formation control agent, or any
combinations thereof. The sintering promoter can be or include
zirconium, iron, magnesium, alumina, bismuth, lanthanum, silicon,
calcium, cerium, yttrium, a silicate, a borate or any combinations
thereof. The sintering promoter can be or include a compound
containing zirconium, iron, magnesium, alumina, bismuth, lanthanum,
silicon, calcium, cerium, yttrium, a silicate, a borate or any
combination thereof.
[0178] The green body material can include at least one binder. The
binder can be or include a wax, a starch, polyvinyl alcohol, a
sodium silicate solution, or a low molecular weight functionalized
polymer (e.g., 1,000 MW to 100,000 MW or 500 MW to 5,000 MW) or any
combinations thereof. A binder may be used to facilitate the
formation of the green body mixture.
[0179] The green body material can further include at least one
dispersant. The dispersant can be or include at least one
surfactant. A dispersant may be used to facilitate a uniform
mixture of alumina or alumina precursor and a siliceous material in
the green body material. Specific dispersants can include, but are
not limited to, DOLAPIX CE 64 (Zschimmer & Schwarz, GmbH),
DARVAN C(RT Vanderbilt Company, Industrial Minerals &
Chemicals) and similar materials which may comprise from about 0%
by weight to about 5% by weight of the green body material or any
other amount to assist in the dispersion of materials.
[0180] The green body material can include at least one fluxing
agent. The fluxing agent can be or include nepheline syenite,
feldspar, synthetic clay, natural clay or any combinations thereof.
The fluxing agent can be present in an amount of from about 0.1 wt
% to about 25 wt %, based on the weight of the green body
material.
[0181] The green body material can further include at least one
slurrying agent. The slurrying agent can be or include water, an
organic solvent or any combinations thereof. The slurrying agent
can be present in an amount of from about 5 wt % to about 60 wt %,
based on solid loading.
[0182] The green body can be formed as one material or can be
formed as one or more layers of green body material. Each layer can
be the same or different from each other with respect to
composition and/or thickness. The thickness of each layer can be
any amount, such as from 1 micron to 1,000 microns. The thickness
can be uniform or non-uniform.
[0183] The green body can be produced by spray drying, die
pressing, extrusion coating, fluidized bed coating, mixer
granulation, high shear mixing, roller compaction injection
molding, tumbling or any combination thereof.
[0184] The green body can further include a template, wherein the
green body material coats, forms a layer(s), or encapsulates the
template, such as a solid or hollow template. The template can be
or include a cenosphere, a micro glass sphere, a synthetic
cenosphere, a polymer bead or any combinations thereof.
[0185] When a template is present and is a cenosphere or other
ceramic material, the sintering in the process of the present
invention can form at least one whisker phase, such as mullite
whisker phase, and an amorphous phase in the template.
[0186] The green body can be formed by deposition of the green body
material onto a template such as a hollow template. The deposition
can be achieved by spray drying, fluidized bed coating or any
combinations thereof. The spray drying can be performed at an air
temperature of from about 40.degree. C. to about 90.degree. C., an
air flow of from about 90 liters per minute to about 150 liters per
minute, and/or a nozzle air pressure of from about 10 psig to about
25 psig.
[0187] The sintering can be performed in the presence of a gas. The
gas can be or include oxygen, such as from about 100 ppm to about
100% by weight oxygen, or from about 250 ppm to about 90% by weight
oxygen, or from about 500 ppm to about 79% by weight oxygen, or
from about 1000 ppm to about 50% by weight oxygen.
[0188] The sintering can occur in any sintering device (e.g.,
furnace, oven) such as with induction heating. The sintering is
controlled so as to promote reactive or reaction sintering and not
solid state sintering. The sintering can occur in a rotary kiln,
microwave, tunnel kiln, shutter kiln, electric furnace, gas
furnace, convection furnace, roller hearth, chain hearth, pusher
sled, vertical shaft furnace or any combinations thereof. The
sintering can be self-propagation high temperature sintering,
radiation sintering, plasma sintering, spark plasma sintering and
the like.
[0189] The sintering can be performed under a pressure of from
about 0.1.times.10.sup.5 Pa to about 10.times.10.sup.5 Pa, such as
from about 0.5.times.10.sup.5 Pa to about 7.times.10.sup.5 Pa, or
from about 1.times.10.sup.5 Pa to about 5.times.10.sup.5 Pa.
[0190] The sintering can be performed at a temperature from about
500.degree. C. to about 2500.degree. C. The sintering can be
performed at an elevated pressure, for instance, at a pressure from
about 0.1 MPa to about 200 MPa for about 1 hour to about 20 hours.
The sintering preferably occurs at a temperature below 1400.degree.
C., such as from 1100.degree. C. to about 1300.degree. C., for
about 30 minutes to 8 hours, and more preferably from 2 to 6 hours.
The sintering temperatures referred to herein are the temperature
of the material being sintered. Other sintering temperatures/times
can be at a temperature from about 1100.degree. C. to about
1300.degree. C. for about 1 hour to about 20 hours. Another example
of the pressure during sintering is from about 0.1 MPa to about 200
MPa.
[0191] The sintering can be performed at any firing rate, such as a
firing rate of from about 0.01.degree. C./min to about 2000.degree.
C./min.
[0192] As indicated above, the final product, for instance formed
from this method or other methods can be composite material, such
as a glass-ceramic composite material that is or includes a
sintered body having at least one whisker phase and an amorphous
phase and optionally, at least one crystalline phase, such as a
crystalline particulate phase. The amorphous phase can be or
include at least one ceramic or metal oxide. The amorphous phase
can further include unreacted particles, such as unreacted metal
oxide(s). The composite material can further include a template.
The template can be a solid or hollow sphere. The hollow sphere can
be or include at least one cenosphere, a micro glass sphere, a
synthetic cenosphere, a polymer bead or any combination thereof.
The template can have or include at least one whisker phase (e.g.,
in-situ mullite whisker phase) and an amorphous phase. The whiskers
in the composite can have diameters of from about 0.05 .mu.M to
about 2 .mu.m, and/or aspect ratios of from about 10 to about 50,
and/or lengths of from about 1 .mu.M to about 50 .mu.m.
[0193] The phases of the glass-ceramic composite can be or have 3-3
connectivity for the whisker phase and the amorphous phase. The
phases of the composite can be or have 3-3-0 connectivity for the
whisker phase, the amorphous phase and the unreacted metal oxide,
respectively. The phases can be or have 3-3-0-0 connectivity for
the whisker phase, the amorphous phase, and the two or more types
of unreacted metal oxide material (unreacted first metal oxide and
unreacted second metal oxide) respectively.
[0194] The amorphous phase can include or be ceramic, and for
instance can include alumina and/or silica. The amorphous phase can
further include unreacted material (e.g., particles), such as
alumina, alumina precursor, siliceous material, and/or the
amorphous material (e.g., perlite) or any combination thereof.
[0195] Referring to the preferred method and starting ingredients,
the final product, for instance, formed from this method or other
methods can be a glass-ceramic composite material that is or
includes a sintered body having at least one whisker phase, such as
a mullite whisker phase, and an amorphous phase. The amorphous
phase can be or include at least one ceramic, such as alumina
and/or silica. The amorphous phase can further include unreacted
particles, such as alumina, alumina precursor, siliceous material
or any combinations thereof. The composite material can further
include a template. The template can be a solid or hollow sphere.
The hollow sphere can be or include at least one cenosphere, a
micro glass sphere, a synthetic cenosphere, a polymer bead or any
combination thereof. The template can have or include at least one
whisker phase, such as a mullite whisker phase, (e.g., in-situ
mullite whisker phase) and an amorphous phase. The whiskers, such
as mullite whiskers, in the glass-ceramic composite can have
diameters of from about 0.05 .mu.m to about 2 .mu.m, and/or aspect
ratios of from about 10 to about 50, and/or lengths of from about 1
.mu.m to about 50 .mu.m.
[0196] The phases of the glass-ceramic composite can be or have 3-3
connectivity for the whisker phase (e.g., mullite whisker phase)
and the amorphous phase. The phases of the glass-ceramic composite
can be or have 3-3-0 connectivity for the whisker phase (e.g.,
mullite whisker phase), the amorphous phase and the unreacted
alumina or alumna precursor, respectively. The phases of the
glass-ceramic composite can be or have 3-3-0 connectivity for the
whisker phase (e.g., mullite whisker phase), the amorphous phase
and the unreacted siliceous material, respectively. The phases of
the glass-ceramic composite can be or have 3-3-0-0 connectivity for
the whisker phase (e.g., mullite whisker phase), the amorphous
phase, the unreacted siliceous material and the unreacted alumina
or alumna precursor, respectively.
[0197] The amorphous phase can include or be ceramic, and for
instance can include alumina and/or silica. The amorphous phase can
further include unreacted material (e.g., particles), such as
alumina, alumina precursor, siliceous material, amorphous material
(e.g., perlite), or any combination thereof.
[0198] As indicated, the composite of the present invention can be
considered a proppant or used as a proppant.
[0199] The proppant can have at least one of the following
characteristics: [0200] a. an overall diameter of from 80 microns
to about 3,000 microns or 90 microns to 2,000 microns; [0201] b.
Krumbein sphericity of at least about 0.5 and a roundness of at
least about 0.5; [0202] c. a crush strength of about 10 MPa or
greater; [0203] d. a specific gravity of from about 1.0 to about
3.0; [0204] e. a porosity of from about 1% to about 70%; [0205] f.
at least 90% (by number or by volume) of proppant pores having a
pore size of from about 0.1 .mu.m to about 10 .mu.m, [0206] g. at
least 80% (by number or by volume) of proppant pores are not in
contact with each other, [0207] h. pores that are generally
spherical in shape and have a smooth, glassy interior surface,
[0208] i. a smooth external surface. All of a. through i. can be
present, or any two, three, four, five, six, seven, or eight of the
properties/characteristics.
[0209] The proppants can be used in a method to prop open
subterranean formation fractures and can involve introducing a
proppant formulation that includes one or proppants of the present
invention, into the subterranean formation. The method can be for
treating a subterranean producing zone penetrated by a well bore,
and can include the steps of preparing or providing a treating
fluid that includes a fluid, energized fluid, foam, or a gas
carrier having the proppant of the present invention suspended
therein, and pumping the treating fluid into the subterranean
producing zone whereby the particles are deposited therein. The
treating fluid can be a fracturing fluid and the proppant particles
can be deposited in the fractures formed in the subterranean
producing zone. The treating fluid can be a gravel packing fluid
and the particles can be deposited in the well bore adjacent to the
subterranean producing zone.
[0210] The present invention further relates to a matrix that
includes a plurality of the proppants of the present invention and
at least one solid matrix material in which the proppant is
distributed.
[0211] The configuration of the glass-ceramic article being formed
can take many shapes including a sphere, elliptical, doughnut
shape, rectangular or any shape necessary to fulfill a useful
application. In the case of a sphere, the sphere can encapsulate a
template. The template may be a hollow or solid, and may be a
glassy or glass-ceramic sphere, or an organic sphere. Hollow
spheres are typically used as templates in applications where it is
desirable to produce particles with low specific gravity. Spheres
with an overall diameter from about 90 .mu.m to about 2000 .mu.m
(e.g., 100 .mu.m or higher) are typical for proppants. FIG. 1 shows
such a proppant with an outer shell and an inner shell. Mechanical
analysis of ceramic or glass-ceramic spheres including a hollow
template under load indicates that tensile stress is the major
cause of the fracture since the ceramic materials are typically
strong in compressive strength but weak in tensile strength.
Because of this, making the inner shell strong and tough has been a
great challenge. The present invention toughens the inner shell by
converting the template into a special textured microstructure with
the toughening agent generated in-situ. The toughening agent can be
entangled whiskers, such as mullite whiskers, with diameters from
about 0.05 .mu.m to about 2 .mu.m, and/or aspect ratios from about
10 to about 50, and/or lengths from about 1 .mu.m to about 50 .mu.m
with the interstitial space filled with glasses (e.g., a glassy
phase or amorphous phase), such as alumina and/or silica and/or
other particulate materials. Any unreacted metal oxide
particulates, such as alumina and/or other particulate ceramic
material(s), can serve as a toughening agent.
[0212] Furthermore, the at least one amorphous material containing
at least one entrapped vaporizable material, when sintered under
controlled conditions, promotes a smooth surface at the template
interface, at the outer surface of the proppant, and/or at any
location within the proppant. Small, spherical pores are produced
by the liberation of water or other vaporizable material under
controlled sintering conditions with a smooth, glassy interior
surface. The smooth surfaces as described above can contribute to
increased strength and toughness in the proppant. The surface
roughness for a proppant made from a green body that included an
amorphous material with an entrapped vaporizable material generally
has a lower surface roughness by at least 1%, at least 5%, at least
10%, at least 15%, at least 20%, compared to the same proppant but
without using an amorphous material having an entrapped vaporizable
material.
[0213] The composition of the outer shell surrounding the template
can be so designed that the components of the outer shell react
with the template (part or all of the template) to convert it in
situ into a preferably tough glass-ceramic structure with a
microstructure having a mullite whisker-reinforced composite. Both
the outer shell and the template can undergo viscous reaction
sintering to produce a glass-ceramic composite with 3-3, 3-3-0,
3-3-0-0, 3-2, 3-2-0, 3-2-0-0, 3-1, 3-1-0 or 3-1-0-0 connectivity in
each phase in the structure. A phase connectivity of 3 means that
the material in that phase is self-connected in three dimensions. A
phase connectivity of 2 means that the material in that phase is
self-connected in two dimensions. A phase connectivity of 1 means
that the material in that phase is self-connected in one dimension.
A phase connectivity of 0 means that the material in that phase is
not self-connected. A 3-3-0 connectivity composite is one where one
phase, typically the glass or ceramic phase, is self connected in
three dimensions, a second phase, typically the infiltrate or
whisker phase, is self connected in three dimensions and a third
phase, typically particulates or other materials embedded in the
glass or ceramic phase is not self connected as in the case of
discrete particles. When the concentration of whiskers, such as
mullite whiskers, is high, the whiskers can have a 3 connectivity
because the whiskers are in close proximity to each other and
become entangled in three dimensions. When the concentration of
whiskers, such as mullite whiskers, is relatively low, the whiskers
can have a 1 connectivity where the whiskers are not in close
proximity and tend to exist as discrete and separate whiskers
aligned in one dimension. A viscous phase is distributed uniformly
around the whiskers and after viscous reaction sintering forms a
glassy phase with 3 connectivity where the glassy material is self
connected in three dimensions. The resulting composite of a high
concentration of whiskers in a glassy matrix has 3-3 connectivity.
Production of the glassy phase can be accomplished by viscous
reaction sintering of a) alumina, aluminum hydroxide, bauxite,
gibbsite, boehmite or diaspore or any combination thereof; and b) a
siliceous material such as ground cenosheres, fly ash, silica,
silicate materials, quartz, feldspar, zeolites, bauxite, calcined
clays or any combination thereof; and c) the at least one amorphous
material containing at least one entrapped vaporizable material
such as water such as perlite, stober silica, or any combination
thereof. There may be, as an option, unreacted particles of
alumina, aluminum hydroxide, bauxite, gibbsite, boehmite or
diaspore, ground cenosheres, fly ash, silica, silicate materials,
quartz, feldspar, zeolites, bauxite, calcined clays, perlite,
pumice, volcanic glass, and/or stober silica remaining in the
glassy phase. These remaining unreacted particles are not
self-connected and have 0 connectivity.
[0214] As mentioned above, it can be difficult to disperse whiskers
in a viscous green body material. A novel element of this invention
is the in situ formation of whiskers in a glassy matrix. As an
example, alumina or alumina precursor particles can be combined
with a siliceous material (e.g., ground cenospheres) in a weight
proportion that favors formation of whiskers, such as mullite
whiskers, under conditions of reactive sintering.
[0215] The proportion of alumina to silica in the green body
mixture of alumina or alumina precursor, siliceous material
preferably ground cenospheres and the at least one amorphous
material containing at least one entrapped vaporizable material
such as water, preferably perlite, can be selected to favor the
formation of whiskers, such as mullite whiskers, in the
glass-ceramic composite matrix. The stoichiometric amount can be
about 28 parts of silica by weight and about 72 parts of alumina by
weight, based on the weight of the green body. The ratio may range
from about 20 parts silica by weight:about 80 parts alumina by
weight to about 60 parts silica by weight:about 40 parts alumina by
weight, based on the weight of the green body.
[0216] In the case of spherical glass-ceramic composite particles
including a hollow template, the composition of the outer shell
preferably has a coefficient of thermal expansion matching that of
the template. If the expansion of the inner and outer shells is
significantly different, cracks may form at the interface between
the inner and outer shell and strength of the resulting particle is
negatively affected. The reactants in the outer shell structure
react during firing at typically 1200.degree. C., but can be in the
range of 1100.degree. C.-1300.degree. C., to form whiskers, such as
mullite whiskers, and alumina/silica composites. The whiskers, such
as mullite whiskers, can form in the outer shell, the template
(inner shell), or both. The sintered shell becomes a glass-ceramic
composite, such as with 3-3-0 connectivity or 3-1-0 connectivity
depending upon the concentration of whiskers, such as mullite
whiskers, formed.
[0217] Examination of fractures in glass-ceramic composites with
whiskers (e.g., mullite whiskers) show the amorphous phase and the
whisker phase. FIG. 2 is an SEM image showing the microstructure of
in-situ formed microwhiskers on the free and fracture surfaces of a
proppant. FIG. 3 shows the pull-out effect of the whiskers was also
observed on the fracture surface of the proppant sample, indicating
the toughening effect of the whiskers. Typically, the diametral
splitting tensile strength of the composites mentioned above is
over 100 MPa (14500 p.s.i.) (e.g., 100 MPa-300 MPa) for an apparent
density around 2.5 g/cm.sup.3.
[0218] In one preferred method, a glass-ceramic composite may be
produced by the following general method. [0219] 1. Alumina,
cenospheres, and perlite are ground into an indicated fine particle
size and particle size distribution. The alumina, cenospheres,
perlite and any other components, can be ground independently and
blended, or they can be blended and then co-milled. In either case,
the alumina can be homogenously mixed with and distributed in the
cenosphere material and the perlite or other ceramic materials or
ingredients. [0220] 2. The alumina, cenospheres, perlite, and any
other components and water are added in a predetermined ratio to a
high intensity mixer, and stirred to form a wet homogeneous
particulate mixture. Optionally, a whisker promoter such as
Fe.sub.2O.sub.3 may be added. Suitable commercially available
intensive stirring or mixing devices used for this purpose can have
a rotatable horizontal or inclined circular table and a rotatable
impacting impeller, such as described in U.S. Pat. No. 3,690,622,
to Brunner, the entire disclosure of which is incorporated herein
by reference. [0221] 3. While the mixture is being stirred,
sufficient water can be added to cause the formation of a
composite, that is essentially spherical pellets of desired size
from the mixture of alumina, cenospheres, perlite and any other
components such that intense mixing action can rapidly disperse the
water throughout the particles. In general, the total quantity of
water that is sufficient to cause essentially spherical pellets to
form is from about 15 to about 30 percent by weight of the mixture
of alumina, cenospheres, perlite and any other components. The
total mixing time can be, for example, from about 2 to about 15
minutes, or other time periods depending on equipment, settings,
compositions, and conditions used. Those of ordinary skill in the
art will understand how to determine a suitable amount of water to
add to the mixer so that substantially round and spherical pellets
are formed. [0222] 4. Optionally, a minor amount of whiskers, such
as mullite whiskers, may be added to the green body material. The
minor amount of whiskers act as seed whiskers to promote the
formation of the whiskers, such as mullite whiskers, (e.g., at an
early stage) in the viscous reactive sintering process. When
materials, such as ground cenospheres of fly ash, are used as the
siliceous material, a minor amount of whiskers, such as mullite
whiskers, can be naturally present in the cenospheres or fly ash
and supplemental addition of mullite whiskers may be avoided. The
presence of seed mullite whiskers is effective in production of a
whisker phase and a glass-ceramic phase in the resulting composite.
[0223] 5. Optionally, a binder, for example, various resins or
waxes, starch, or polyvinyl alcohol, may be added to the initial
mixture to improve the formation of pellets and to increase the
green strength of the unsintered pellets. Suitable binders include,
but are not limited to, corn starch, polyvinyl alcohol or sodium
silicate solution, or a blend thereof. Liquid binders can be added
to the mixture and bentonite and/or various resins or waxes known
and available to those of ordinary skill in the art may also be
used as a binder. A suitable binder can be, for example, CERAFIX
K33 (Zschimmer & Schwarz, Inc.--U.S. Division, Milledgeville,
Ga.) or PVA 405 (Kuraray America, Inc., Houston, Tex.) and similar
materials, which may be added at levels of from about 0 percent by
weight to 10% by weight, or from 0.25% by weight to 1% by weight,
or any other amount so as to assist formation of the pellets.
Whether to use more or less binder than the values reported herein
can be determined by one of ordinary skill in the art through
routine experimentation. [0224] 6. Optionally, a dispersant such as
a surfactant may be added to the initial mixture to improve the
homogeneity of the green body material, improve the dispersion of
particulates such as the metal oxide(s), pore formers such as SiC,
binder and other materials and decrease the number of pore former
particles that are in contact with each other. The dispersant also
effectively reduces the time required to make a uniform mixture.
Specific dispersants can include but are not limited to DOLAPIX CE
64 (Zschimmer & Schwarz, GmbH), DARVAN C(RT Vanderbilt Company,
Industrial Minerals & Chemicals) and similar materials which
may be present in an amount of from about 0% by weight to about 5%
by weight of the green body material or any other amount to assist
in the dispersion of materials in the slurrying agent. [0225] 7.
Optionally, a sintering aid may be added to the initial mixture to
enhance the bonding of particles in the ceramic and speed the
sintering process by providing an internal source of oxygen.
Sintering aids can include, but are not limited to, magnesium oxide
(MgO), yttrium oxide (Y.sub.2O.sub.3) and cerium oxides (CeO.sub.2,
Ce.sub.2O.sub.3). Sintering aids may be present in an amount of
from about 0% to about 5% by weight of the green body material or
any other amount to enhance and speed the sintering process. [0226]
8. Optionally, a fluxing agent may be added to the mixture to
enhance the effect of the perlite to promote smooth surfaces and
interfaces between material phases; to enhance the production of
small, substantially spherical pores with a smooth glassy interior
surface; and/or to enhance formation of a smooth surface on the
outer surface of the proppant. Fluxing agents can include nepheline
syenite, feldspar, synthetic clay, natural clay, or any combination
thereof [0227] 9. The resulting pellets can be dried and screened
to an appropriate pre-sintering size that can compensate for
shrinkage that occurs during sintering. Rejected oversized and
undersized pellets and powdered material obtained after the drying
and screening steps may be recycled. The pellets may also be
screened either before drying or after firing or both. [0228] 10.
The dried pellets are then fired at a sintering temperature for a
period sufficient to enable recovery of sintered, spherical pellets
having at least one whisker phase, such as a mullite whisker phase;
small, substantially spherical pores with a smooth glassy interior
surface; a smooth, glassy surface on the outer surface of the
proppant; and at least one amorphous phase meeting predetermined
strength specifications. The sintered pellets can be screened for
sizing purposes.
[0229] The present invention includes the following
aspects/embodiments/features in any order and/or in any
combination: [0230] 1. The present invention relates to a method
for producing a proppant comprising [0231] a. forming a green body
from a green body material comprising [0232] i. at least one metal
oxide or precursor thereof that is capable of forming whiskers in
said proppant and as part of said proppant, [0233] ii. at least one
amorphous material containing at least one entrapped vaporizable
material, [0234] iii. preformed whiskers, and [0235] iv. at least
one whisker promoter, optionally in the absence of fluorine or
fluorine compounds; [0236] b. reactive sintering said green body
under reactive sintering conditions to form a sintered body
comprising whiskers and at least one amorphous phase. [0237] 2. The
proppant of any preceding or following embodiment/feature/aspect,
wherein said metal oxide comprises alumina. [0238] 3. The proppant
of any preceding or following embodiment/feature/aspect, wherein
said alumina has a specific surface area of from 1 to about 50
m.sup.2/g. [0239] 4. The proppant of any preceding or following
embodiment/feature/aspect, wherein said metal oxide comprises
bauxite, alpha, gamma, and/or theta alumina. [0240] 5. The proppant
of any preceding or following embodiment/feature/aspect, wherein
said at least one metal oxide comprises a first metal oxide and a
second metal oxide, wherein said first metal oxide and said second
metal oxide are different from each other. [0241] 6. The proppant
of any preceding or following embodiment/feature/aspect, wherein
said at least one metal oxide comprises a first metal oxide and a
second metal oxide, wherein said first metal oxide and said second
metal oxide are different from each other with respect to metal
that forms the oxide. [0242] 7. The proppant of any preceding or
following embodiment/feature/aspect, wherein said amorphous
material comprises perlite, stober silica, pumice, andesite,
scoria, volcanic glasses, or any combination thereof. [0243] 8. The
proppant of any preceding or following embodiment/feature/aspect,
wherein said vaporizable material comprises water (H.sub.2O) carbon
dioxide (CO.sub.2), sulfur dioxide (SO.sub.2), hydrogen sulfide
(H.sub.2S), nitrogen, argon, helium, neon, methane, carbon monoxide
(CO), hydrogen, oxygen, hydrogen chloride (HCl), hydrogen fluoride
(HF), hydrogen bromide (HBr), nitrogen oxide (NOx), sulfur
hexafluoride (SF.sub.6), carbonyl sulfide (COS), volcanic gases, or
any combination thereof. [0244] 9. The proppant of any preceding or
following embodiment/feature/aspect, wherein said amorphous
material has a lower specific gravity than other said green body
materials. [0245] 10. The proppant of any preceding or following
embodiment/feature/aspect, wherein said method further comprises
forming said green body on a template that is porous or non-porous.
[0246] 11. The proppant of any preceding or following
embodiment/feature/aspect, wherein said method further comprises
forming said green body around a template so as to encapsulate said
template. [0247] 12. The proppant of any preceding or following
embodiment/feature/aspect, wherein said template is a sphere.
[0248] 13. The proppant of any preceding or following
embodiment/feature/aspect, wherein said template is a hollow
sphere. [0249] 14. The proppant of any preceding or following
embodiment/feature/aspect, wherein said template is a solid sphere.
[0250] 15. The proppant of any preceding or following
embodiment/feature/aspect, wherein said template is a cenosphere.
[0251] 16. The proppant of any preceding or following
embodiment/feature/aspect, wherein said template is an agglomerated
mullite or alumina particles (e.g., particle size range of from 20
.mu.m to 500 .mu.m, such as 100-200 .mu.m). [0252] 17. The proppant
of any preceding or following embodiment/feature/aspect, wherein
said reactive sintering at least partially converts said template
to a template comprising in-situ whiskers and at least one
amorphous phase. [0253] 18. The proppant of any preceding or
following embodiment/feature/aspect, wherein concentration of
in-situ whiskers in said template is different from concentration
of whiskers in said sintered body that is on said template. [0254]
19. The proppant of any preceding or following
embodiment/feature/aspect, wherein said whiskers comprise mineral
or metal oxide whiskers. [0255] 20. A proppant comprising a
sintered body, wherein said sintered body comprises whiskers and at
least one amorphous phase. [0256] 21. The proppant of any preceding
or following embodiment/feature/aspect, wherein said whiskers
comprise in-situ whiskers. [0257] 22. The proppant of any preceding
or following embodiment/feature/aspect, wherein said whiskers are
present as a whisker phase that is a continuous phase and
optionally, said proppant further comprising at least one
crystalline particulate phase. [0258] 23. The proppant of any
preceding or following embodiment/feature/aspect, wherein said
whiskers are present as a whisker phase that is a non-continuous
phase. [0259] 24. The proppant of any preceding or following
embodiment/feature/aspect, wherein said whiskers are uniformly
distributed throughout said sintered body. [0260] 25. The proppant
of any preceding or following embodiment/feature/aspect, wherein
whiskers are present in said sintered body in a three-dimensional
non-woven structure. [0261] 26. The proppant of any preceding or
following embodiment/feature/aspect, wherein said whiskers have a
phase connectivity of 3. [0262] 27. The proppant of any preceding
or following embodiment/feature/aspect, wherein said whiskers have
a phase connectivity of 2. [0263] 28. The proppant of any preceding
or following embodiment/feature/aspect, wherein said whiskers are
metal oxide or mineral derived whiskers. [0264] 29. The proppant of
any preceding or following embodiment/feature/aspect, further
comprising a template. [0265] 30. The proppant of any preceding or
following embodiment/feature/aspect, wherein said template is a
sphere. [0266] 31. The proppant of any preceding or following
embodiment/feature/aspect, wherein said template is a hollow
sphere. [0267] 32. The proppant of any preceding or following
embodiment/feature/aspect, wherein said template is a cenosphere.
[0268] 33. The proppant of any preceding or following
embodiment/feature/aspect, wherein said sintered body encapsulates
said template. [0269] 34. The proppant of any preceding or
following embodiment/feature/aspect, wherein said template
comprises whiskers and at least one amorphous phase. [0270] 35. The
proppant of any preceding or following embodiment/feature/aspect,
wherein said template comprises whiskers and at least one amorphous
phase wherein concentration of whiskers in said template is
different from concentration of whiskers in said sintered body that
is on said template. [0271] 36. The proppant of any preceding or
following embodiment/feature/aspect, wherein said template comprise
whiskers and at least one amorphous phase wherein concentration of
whiskers in said template is lower than concentration of whiskers
in said sintered body that is on said template. [0272] 37. The
proppant of any preceding or following embodiment/feature/aspect,
wherein said whiskers in said template and in said sintered body
comprise mineral or metal oxide derived whiskers. [0273] 38. The
proppant of any preceding or following embodiment/feature/aspect,
wherein said proppant has at least one of the following
characteristics: [0274] a. an overall diameter of from about 90
microns to about 2,000 microns; [0275] b. a Krumbein sphericity of
at least about 0.5 and a roundness of at least about 0.5; [0276] c.
a crush strength of about 10 MPa or greater; [0277] d. a specific
gravity of from about 1.0 to about 3.0; [0278] e. a porosity of
from about 6% to about 40%; [0279] f. at least 90% of proppant
pores having a pore size of from about 0.1 .mu.m to about 10 .mu.m,
and [0280] g. at least 80% of proppant pores are not in contact
with each other. [0281] 39. A method to prop open subterranean
formation fractures comprising introducing a proppant formulation
comprising the proppant of any preceding or following
embodiment/feature/aspect into a subterranean formation. [0282] 40.
A method of treating a subterranean producing zone penetrated by a
well bore comprising the steps of: [0283] a. preparing or providing
a treating fluid that comprises a fluid, energized fluid, foam, or
a gas carrier having the proppant of any preceding or following
embodiment/feature/aspect suspended therein, and [0284] b. pumping
said treating fluid into said subterranean producing zone whereby
said particles are deposited therein. [0285] 41. The method of any
preceding or following embodiment/feature/aspect, wherein said
treating fluid is a fracturing fluid and said particles are
deposited in fractures formed in said subterranean producing zone.
[0286] 42. The method of any preceding or following
embodiment/feature/aspect, wherein said treating fluid is a gravel
packing fluid and said particles are deposited in said well bore
adjacent to said subterranean producing zone. [0287] 43. A method
for producing a glass-ceramic composite comprising [0288] a.
forming a green body from a green body material comprising [0289]
i. alumina and/or at least one alumina precursor and a siliceous
material in a ratio to form whiskers in said glass-ceramic
composite, and [0290] ii. at least one amorphous material
containing at least one entrapped vaporizable material, and [0291]
iii. whiskers, and [0292] iv. at least one whisker promoter in the
absence of fluorine or fluorine compounds; [0293] b. sintering said
green body under sintering conditions to form in situ said
glass-ceramic composite comprising at least one mullite whisker
phase and at least one amorphous phase. [0294] 44. The method of
any preceding or following embodiment/feature/aspect, wherein said
whiskers in i. and/or iii. are mullite whiskers. [0295] 45. The
method of any preceding or following embodiment/feature/aspect,
wherein said alumina precursor comprises aluminum hydroxide,
bauxite, gibbsite, boehmite or diaspore or any combination thereof.
[0296] 46. The method of any preceding or following
embodiment/feature/aspect, wherein said alumina or alumina
precursor has a particle size distribution, d.sub.as, from about
0.5 to about 15, wherein,
d.sub.as={(d.sub.a90-d.sub.a10)/d.sub.a50} wherein d.sub.a10 is a
particle size wherein 10% of the particles have a smaller particle
size, d.sub.a50 is a median particle size wherein 50% of the
particles have a smaller particle size, and d.sub.a90 is a particle
size wherein 90% of the particle volume has a smaller particle
size. [0297] 47. The method of any preceding or following
embodiment/feature/aspect, wherein said alumina or alumina
precursor has a particle size distribution, d.sub.as, from about
1.0 to about 6.0. [0298] 48. The method of any preceding or
following embodiment/feature/aspect, wherein the median particle
size, d.sub.a50, of said alumina or alumina precursor is from about
0.01 .mu.m to about 100 .mu.m, wherein d.sub.a50 is a median
particle size where 50% of the particles of the distribution have a
smaller particle size. [0299] 49. The method of any preceding or
following embodiment/feature/aspect, wherein the median particle
size, d.sub.a50, of said alumina or alumina precursor is from about
1 .mu.m to about 5 .mu.m, wherein d.sub.a50 is a median particle
size where 50% of the particles of the distribution have a smaller
particle size. [0300] 50. The method of any preceding or following
embodiment/feature/aspect, wherein said siliceous material
comprises cenospheres, fly ash or any combination thereof. [0301]
51. The method of any preceding or following
embodiment/feature/aspect, wherein said siliceous material
comprises silicate materials, quartz, feldspar, zeolites, bauxite,
calcined clays or any combination thereof [0302] 52. The method of
any preceding or following embodiment/feature/aspect, wherein said
siliceous material has a particle size distribution, d.sub.ss, from
about 0.5 to about 15, wherein,
d.sub.ss={(d.sub.s90-d.sub.s10)/d.sub.s50} wherein d.sub.s10 is a
particle size wherein 10% of the particles have a smaller particle
size, d.sub.s50 is a median particle size wherein 50% of the
particles have a smaller particle size, and d.sub.s90 is a particle
size wherein 90% of the particle volume has a smaller particle
size. [0303] 53. The method of any preceding or following
embodiment/feature/aspect, wherein said siliceous material has a
particle size distribution, d.sub.ss, from about 1.0 to about 6.0.
[0304] 54. The method of any preceding or following
embodiment/feature/aspect, wherein the median particle size,
d.sub.s50, of said siliceous material is from about 0.01 .mu.m to
about 100 .mu.m, wherein d.sub.s50 is a median particle size where
50% of the particles of the distribution have a smaller particle
size. [0305] 55. The method of any preceding or following
embodiment/feature/aspect, wherein the median particle size,
d.sub.s50, of said siliceous material is from about 1 .mu.m to
about 5 .mu.m, wherein d.sub.s50 is a median particle size where
50% of the particles of the distribution have a smaller particle
size. [0306] 56. The method of any preceding or following
embodiment/feature/aspect, wherein said amorphous material
containing at least one entrapped vaporizable material comprises
perlite, a stober silica, pumice, andesite, scoria, volcanic
glasses or any combination thereof. [0307] 57. The method of any
preceding or following embodiment/feature/aspect, wherein said
vaporizable material comprises water (H.sub.2O), carbon dioxide
(CO.sub.2), sulfur dioxide (SO.sub.2), hydrogen sulfide (H.sub.2S),
nitrogen, argon, helium, neon, methane, carbon monoxide (CO),
hydrogen, oxygen, hydrogen chloride (HCl), hydrogen fluoride (HF),
hydrogen bromide (HBr), nitrogen oxide (NOx), sulfur hexafluoride
(SF.sub.6), carbonyl sulfide (COS), volcanic gases, or any
combination thereof [0308] 58. The method of any preceding or
following embodiment/feature/aspect, wherein said amorphous
material containing at least one entrapped vaporizable material has
a particle size distribution, d.sub.as, from about 1.0 to about
6.0. [0309] 59. The method of any preceding or following
embodiment/feature/aspect, wherein the median particle size,
d.sub.a50, of said amorphous material containing at least one
entrapped vaporizable material is from about 0.01 .mu.m to about
100 .mu.m, wherein d.sub.a50 is a median particle size where 50% of
the particles of the distribution have a smaller particle size.
[0310] 60. The method of any preceding or following
embodiment/feature/aspect, wherein the median particle size,
d.sub.a50, of said amorphous material containing at least one
entrapped vaporizable material is from about 1 .mu.m to about 5
.mu.
m, wherein d.sub.a50 is a median particle size where 50% of the
particles of the distribution have a smaller particle size. [0311]
61. The method of any preceding or following
embodiment/feature/aspect, wherein said ratio to form whiskers in
said glass-ceramic composite is from about 20% SiO.sub.2
material/80% Al.sub.2O.sub.3 or alumina precursor by weight to
about 60% siliceous material/40% alumina or alumina precursor by
weight. [0312] 62. The method of any preceding or following
embodiment/feature/aspect, wherein said mullite whiskers are
naturally occurring in cenospheres and comprise from about 2% by
weight to about 40% by weight of the cenospheres, wherein said
siliceous material comprises cenospheres, and wherein said
cenospheres contain said mullite whiskers. [0313] 63. The method of
any preceding or following embodiment/feature/aspect, wherein said
mullite whiskers comprises from about 0.5% by weight to about 20%
by weight of said green body material. [0314] 64. The method of any
preceding or following embodiment/feature/aspect, wherein said
whisker promoter comprises B.sub.2O.sub.3 and/or at least one
transition metal oxide. [0315] 65. The method of any preceding or
following embodiment/feature/aspect, wherein said transition metal
oxide comprises Fe.sub.2O.sub.3, TiO.sub.2, CoO, NiO, or any
combination thereof. [0316] 66. The method of any preceding or
following embodiment/feature/aspect, wherein said whisker promoter
comprises from about 1% by weight to about 2% by weight of said
green body mixture. [0317] 67. The method of any preceding or
following embodiment/feature/aspect, wherein said sintering is
performed in the presence of a gas. [0318] 68. The method of any
preceding or following embodiment/feature/aspect, wherein said gas
comprises from about 100 ppm to about 100% by weight oxygen. [0319]
69. The method of any preceding or following
embodiment/feature/aspect, wherein said gas comprises from about
250 ppm to about 90% by weight oxygen. [0320] 70. The method of any
preceding or following embodiment/feature/aspect, wherein said gas
comprises from about 500 ppm to about 79% by weight oxygen. [0321]
71. The method of any preceding or following
embodiment/feature/aspect, wherein said gas comprises from about
1000 ppm to about 50% by weight oxygen. [0322] 72. The method of
any preceding or following embodiment/feature/aspect, wherein said
sintering comprises induction heating, rotary kiln, microwave,
tunnel kiln, shutter kiln, electric furnace, gas furnace,
convection furnace, self-propagation high temperature sintering,
radiation, plasma, spark plasma, roller hearth, chain hearth,
pusher sled, vertical shaft furnace or any combination thereof.
[0323] 73. The method of any preceding or following
embodiment/feature/aspect, wherein said sintering is performed
under a pressure of from about 0.1.times.10.sup.5 Pa to about
10.times.10.sup.5 Pa. [0324] 74. The method of any preceding or
following embodiment/feature/aspect, wherein said sintering is
performed under a pressure of from about 0.5.times.10.sup.5 Pa to
about 7.times.10.sup.5 Pa. [0325] 75. The method of any preceding
or following embodiment/feature/aspect, wherein said sintering is
performed under a pressure of from about 1.times.10.sup.5 Pa to
about 5.times.10.sup.5 Pa. [0326] 76. The method of any preceding
or following embodiment/feature/aspect, wherein said sintering is
performed at a temperature from about 500.degree. C. to about
2500.degree. C. and said pressure is from about 0.1 MPa to about
200 MPa for about 1 hour to about 20 hours. [0327] 77. The method
of any preceding or following embodiment/feature/aspect, wherein
said sintering is performed at a temperature from about
1000.degree. C. to about 1400.degree. C. and said pressure is from
about 0.1 MPa to about 200 MPa for about one half hour to about 20
hours. [0328] 78. The method of any preceding or following
embodiment/feature/aspect, wherein said sintering is performed at a
firing rate from about 0.01.degree. C./min to about 2000.degree.
C./min. [0329] 79. The method of any preceding or following
embodiment/feature/aspect, wherein the green body material further
comprises at least one sintering promoter comprising a sintering
aid, a glassy phase formation agent, a grain growth inhibitor, a
ceramic strengthening agent, a crystallization control agent, or
phase formation control agent, or any combination thereof. [0330]
80. The method of any preceding or following
embodiment/feature/aspect, wherein said sintering promoter
comprises sodium, potassium, cesium (all alkalines) zirconium,
iron, magnesium, alumina, bismuth, lanthanum, silicon, calcium,
cerium, yttrium, a silicate, a borate or any combination thereof.
[0331] 81. The method of any preceding or following
embodiment/feature/aspect, wherein said sintering promoter
comprises a compound containing an alkaline compound(s), e.g.,
zirconium, iron, magnesium, alumina, bismuth, lanthanum, silicon,
calcium, cerium, yttrium, a silicate, a borate or any combination
thereof. [0332] 82. The method of any preceding or following
embodiment/feature/aspect, wherein said green body material further
comprises a binder. [0333] 83. The method of any preceding or
following embodiment/feature/aspect, wherein said binder comprises
a wax, a starch, polyvinyl alcohol, a sodium silicate solution, a
low molecular weight functionalized polymer or any combination
thereof. [0334] 84. The method of any preceding or following
embodiment/feature/aspect, wherein said green body material further
comprises a dispersant. [0335] 85. The method of any preceding or
following embodiment/feature/aspect, wherein said dispersant
comprises a surfactant. [0336] 86. The method of any preceding or
following embodiment/feature/aspect, wherein said green body
material further comprises at least one slurrying agent. [0337] 87.
The method of any preceding or following embodiment/feature/aspect,
wherein said slurrying agent comprises water, an organic solvent or
any combination thereof. [0338] 88. The method of any preceding or
following embodiment/feature/aspect, wherein said green body
material further comprises at least one fluxing agent. [0339] 89.
The method of any preceding or following embodiment/feature/aspect,
wherein said fluxing agent comprises nepheline syenite, feldspar,
synthetic clay, natural clay or any combination thereof. [0340] 90.
The method of any preceding or following embodiment/feature/aspect,
wherein said green body comprises at least one or more layers of
said green body material. [0341] 91. The method of any preceding or
following embodiment/feature/aspect, wherein said layers are of
differing compositions of said green body material. [0342] 92. The
method of any preceding or following embodiment/feature/aspect,
wherein said mullite whiskers in said glass-ceramic composite have
diameters from about 0.05 .mu.m to about 2 .mu.m, aspect ratios
from about 10 to about 50, and lengths from about 1 .mu.m to about
50 .mu.m. [0343] 93. The method of any preceding or following
embodiment/feature/aspect, wherein the phases of said glass-ceramic
composite comprises 3-3 connectivity for the mullite whisker phase
and the amorphous phase. [0344] 94. The method of any preceding or
following embodiment/feature/aspect, wherein the phases of said
glass-ceramic composite comprises 3-3-0 connectivity for the
mullite whisker phase, the amorphous phase and the unreacted
alumina or alumna precursor. [0345] 95. The method of any preceding
or following embodiment/feature/aspect, wherein the phases of said
glass-ceramic composite comprises 3-3-0 connectivity for the
mullite whisker phase, the amorphous phase and the unreacted
siliceous material. [0346] 96. The method of any preceding or
following embodiment/feature/aspect, wherein the phases of said
glass-ceramic composite comprises 3-3-0 connectivity for the
mullite whisker phase, the amorphous phase and the amorphous
material containing at least one entrapped vaporizable material.
[0347] 97. The method of any preceding or following
embodiment/feature/aspect, wherein the phases of said glass-ceramic
composite comprises 3-3-0-0-0 connectivity for the mullite whisker
phase, the amorphous phase, the unreacted siliceous material, the
unreacted alumina or alumna precursor, and the amorphous material
containing at least one entrapped vaporizable material. [0348] 98.
The method of any preceding or following embodiment/feature/aspect,
wherein said amorphous phase consists of at least one ceramic
comprising alumina, silica, the amorphous material containing at
least one entrapped vaporizable material or any combination
thereof. [0349] 99. The method of any preceding or following
embodiment/feature/aspect, wherein said amorphous phase further
comprises unreacted particles of alumina, alumina precursor,
siliceous material, amorphous material containing at least one
entrapped vaporizable material or any combination thereof. [0350]
100. The method of any preceding or following
embodiment/feature/aspect, wherein said forming a green body is
produced by spray coating, die pressing, extrusion coating,
fluidized bed coating, mixer granulation, high shear mixing, roller
compaction injection molding, tumbling or any combination thereof
[0351] 101. The method of any preceding or following
embodiment/feature/aspect, wherein said green body further
comprises a hollow template. [0352] 102. The method of any
preceding or following embodiment/feature/aspect, wherein said
hollow template comprises a cenosphere, a micro glass sphere, a
synthetic cenosphere, a polymer bead or any combination thereof
[0353] 103. The method of any preceding or following
embodiment/feature/aspect, wherein said green body further
comprises a hollow template and said sintering forms at least one
whisker phase and an amorphous phase in said template. [0354] 104.
The method of any preceding or following embodiment/feature/aspect,
wherein said green body is formed by deposition of said green body
material onto said hollow template. [0355] 105. The method of any
preceding or following embodiment/feature/aspect, wherein said
deposition comprises, fluidized bed spray coating or any
combination thereof. [0356] 106. The method of any preceding or
following embodiment/feature/aspect, wherein said spray coating is
performed at an air temperature from about 40.degree. C. to about
90.degree. C., air flow from about 90 liters per minute to about
150 liters per minute, and nozzle air pressure from about 10 psig
to about 25 psig. [0357] 107. A glass-ceramic composite material
comprising a sintered body having at least one whisker phase and an
amorphous phase and optionally, at least one crystalline
particulate phase. [0358] 108. The glass-ceramic composite material
of any preceding or following embodiment/feature/aspect, wherein
said whisker phase is a mullite whisker phase. [0359] 109. The
glass-ceramic composite material of any preceding or following
embodiment/feature/aspect, wherein said amorphous phase is a
ceramics comprising alumina, silica and any combination thereof.
[0360] 110. The glass-ceramic composite material of any preceding
or following embodiment/feature/aspect, wherein said amorphous
phase further comprises unreacted particles of alumina, alumina
precursor, siliceous material, amorphous material containing at
least one entrapped vaporizable material or any combination
thereof. [0361] 111. The glass-ceramic composite material of any
preceding or following embodiment/feature/aspect, further
comprising a template. [0362] 112. The glass-ceramic composite
material of any preceding or following embodiment/feature/aspect,
wherein said template is a hollow sphere comprising a cenosphere, a
micro glass sphere, a synthetic cenosphere, a polymer bead or any
combination thereof. [0363] 113. The glass-ceramic composite
material of any preceding or following embodiment/feature/aspect,
wherein said template is a solid sphere. [0364] 114. The
glass-ceramic composite material of any preceding or following
embodiment/feature/aspect, wherein said template comprises at least
one whisker phase and an amorphous phase. [0365] 115. The
glass-ceramic composite material of any preceding or following
embodiment/feature/aspect, wherein said whiskers in said
glass-ceramic composite have diameters from about 0.05 .mu.m to
about 2 .mu.m, aspect ratios from about 10 to about 50, and lengths
from about 1 .mu.m to about 50 .mu.m. [0366] 116. The glass-ceramic
composite material of any preceding or following
embodiment/feature/aspect, wherein the phases of said glass-ceramic
composite comprises 3-3 connectivity for the whisker phase and the
amorphous phase. [0367] 117. The glass-ceramic composite material
of any preceding or following embodiment/feature/aspect, wherein
the phases of said glass-ceramic composite comprises 3-3-0
connectivity for the whisker phase, the amorphous phase and the
unreacted alumina or alumna precursor. [0368] 118. The
glass-ceramic composite material of any preceding or following
embodiment/feature/aspect, wherein the phases of said glass-ceramic
composite comprises 3-3-0 connectivity among the whisker phase, the
amorphous phase and the unreacted alumina or alumna precursor.
[0369] 119. The glass-ceramic composite material of any preceding
or following embodiment/feature/aspect, wherein the phases of said
glass-ceramic composite comprises 3-3-0 connectivity among the
whisker phase, the amorphous phase and the amorphous material
containing at least one entrapped vaporizable material. [0370] 120.
The glass-ceramic composite material of any preceding or following
embodiment/feature/aspect, wherein the phases of said glass-ceramic
composite comprises 3-3-0-0-0 connectivity for the whisker phase,
the amorphous phase, the unreacted alumina material, the unreacted
siliceous material, and the amorphous material containing at least
one entrapped vaporizable material. [0371] 121. The glass-ceramic
composite material of any preceding or following
embodiment/feature/aspect, wherein said composite has at least one
of the following characteristics: [0372] a. an overall diameter of
from about 90 microns to about 2,000 microns; [0373] b. a Krumbein
sphericity of at least about 0.5 and a roundness of at least about
0.5; [0374] c. a crush strength of about 10 MPa or greater; [0375]
d. a specific gravity of from about 1.0 to about 3.0; [0376] e. a
porosity of from about 6% to about 40%; [0377] f. at least 90% of
proppant pores having a pore size of from about 0.1 .mu.m to about
10 .mu.m, [0378] g. at least 80% of proppant pores are not in
contact with each other. [0379] 122. A method to prop open
subterranean formation fractures comprising introducing a proppant
formulation comprising the proppant of any preceding or following
embodiment/feature/aspect into a subterranean formation. [0380]
123. A method of treating a subterranean producing zone penetrated
by a well bore comprising the steps of:
[0381] a. preparing or providing a treating fluid that comprises a
fluid, energized fluid, foam, or a gas carrier having the proppant
of any preceding or following embodiment/feature/aspect suspended
therein, and [0382] b. pumping said treating fluid into said
subterranean producing zone whereby said particles are deposited
therein. [0383] 124. The method of any preceding or following
embodiment/feature/aspect, wherein said treating fluid is a
fracturing fluid and said particles are deposited in fractures
formed in said subterranean producing zone. [0384] 125. The method
of any preceding or following embodiment/feature/aspect, wherein
said treating fluid is a gravel packing fluid and said particles
are deposited in said well bore adjacent to said subterranean
producing zone. [0385] 126. A matrix comprising a plurality of the
proppant of any preceding or following embodiment/feature/aspect
and at least one solid matrix material in which the proppant is
distributed. [0386] 127. A method for producing a proppant
comprising [0387] a. forming a green body from a green body
material comprising [0388] i. at least one metal oxide or precursor
thereof that is capable of forming whiskers in said proppant and as
part of said proppant, and [0389] ii. at least one amorphous
material containing at least one entrapped vaporizable material,
and [0390] iii. optionally preformed whiskers, and [0391] iv. at
least one whisker promoter, optionally in the absence of fluorine
or fluorine compounds; and [0392] v. at least one carbide or metal
carbide, [0393] b. reactive sintering said green body under
reactive sintering conditions to form a sintered body comprising
in-situ whiskers and at least one amorphous phase. [0394] 128. The
method of any preceding or following embodiment/feature/aspect,
wherein said carbide is SiC. [0395] 129. A proppant comprising a
sintered body, wherein said sintered body comprises whiskers, at
least one glassy phase, and at least one amorphous phase. [0396]
130. The proppant of any preceding or following
embodiment/feature/aspect, wherein said sintered body further
comprises at least one carbide or metal carbide. [0397] 131. The
proppant of any preceding or following embodiment/feature/aspect,
wherein said at least one carbide is SiC. [0398] 132. The proppant
of any preceding or following embodiment/feature/aspect, wherein
said at least one carbide or metal carbide is present in an amount
of from 1% by weight to 25% by weight, based on the weight of the
proppant. [0399] 133. The proppant of any preceding or following
embodiment/feature/aspect, further comprising at least one carbide
or metal carbide in particulate form, and at least one crystalline
particulate phase. [0400] 134. The proppant of any preceding or
following embodiment/feature/aspect, wherein said at least one
crystalline particulate phase is alumina. [0401] 135. The proppant
of any preceding or following embodiment/feature/aspect, wherein
said whiskers are present as an in-situ whisker phase that is a
continuous phase and optionally, at least one crystalline
particulate phase. [0402] 136. The proppant of any preceding or
following embodiment/feature/aspect, wherein said whiskers are
present as an in-situ whisker phase that is a non-continuous phase.
[0403] 137. The proppant of any preceding or following
embodiment/feature/aspect, wherein said whiskers are uniformly
distributed throughout said sintered body. [0404] 138. The proppant
of any preceding or following embodiment/feature/aspect, wherein
in-situ whiskers are present in said sintered body in a
three-dimensional non-woven structure. [0405] 139. A proppant
comprising a sintered sphere having a Krumbein sphericity of at
least about 0.5 and a roundness of at least about 0.4, and wherein
said sphere comprises a) a plurality of ceramic whiskers or oxides
thereof and b) a glassy phase and c) optionally at least one
non-whisker crystalline phase and d) optionally a plurality of
microspheres, wherein said sintered sphere has a diameter of from
about 90 microns to 2,500 microns, and said sintered sphere has a
specific gravity of from 0.8 g/cc to about 3.8 g/cc, and said
proppant has a crush strength of from about 1,000 psi or greater,
and wherein said proppant includes one or more of the following
characteristics: [0406] 1) said glassy phase is present in an
amount of at least 10% by weight, based on the weight of the
proppant; [0407] 2) said ceramic whiskers have an average length of
less than 3.2 microns; [0408] 3) said ceramic whisker have an an
average width of less than 0.35 micron; [0409] 4) said ceramic
whiskers have a whisker length distribution, d.sub.as, of about 8
or less, wherein, d.sub.as={(d.sub.a90-d.sub.a10)/d.sub.a50}
wherein d.sub.a10 is a whisker length wherein 10% of the whiskers
have a smaller length, d.sub.a50 is a median whisker length wherein
50% of the whiskers have a smaller whisker length, and d.sub.a90 is
a whisker length wherein 90% of the whiskers have a smaller whisker
length; [0410] 5) said proppant having a specific gravity of from
1.6 to 1.8 with a crush strength of at least 2000 psi; [0411] 6)
said proppant having a specific gravity of from 1.8 to 2 with a
crush strength of at least 3000 psi; [0412] 7) said proppant having
a specific gravity of from 2 to 2.1 with a crush strength of at
least 5,000 psi; [0413] 8) said proppant having a specific gravity
of from 2.25 to 2.35 with a crush strength of at least 8,000 psi;
[0414] 9) said proppant having a specific gravity of from 2.5 to
3.2 with a crush strength of at least 12,000 psi; [0415] 10) said
proppant having a specific gravity of from 2.5 to 3.2 with a crush
strength of at least 18,000 psi; [0416] 11) said proppant having a
combined clay amount and cristobalite amount of less than 20% by
weight of proppant; [0417] 12) said proppant having an free
alpha-alumina content of at least 5% by weight of said proppant;
[0418] 13) said proppant having an HF etching weight loss of less
than 35% by weight of said proppant; [0419] 14) said proppant
having said microspheres present as hollow glass microspheres
having a particle size distribution, d.sub.as, of from about 0.5 to
about 2.7, wherein, d.sub.as={(d.sub.a90-d.sub.a50)/d.sub.a50}
wherein d.sub.10 is a particle size wherein 10% of the particles
have a smaller particle size, d.sub.50 is a median particle size
wherein 50% of the particles have a smaller particle size, and
d.sub.a90 is a particle size wherein 90% of the particle volume has
a smaller particle size; [0420] 15) said proppant having
microspheres present wherein said microspheres are uniformly
present in said proppant or in a layered region of said proppant;
[0421] 16) said ceramic whiskers are present in an amount of from
5% to 60% by weight of said proppant. [0422] 17) said proppant has
a combined clay amount and cristobalite amount of less than 20% by
weight of proppant and said mullite whiskers are present in an
amount of 60% or more by weight of said proppant; [0423] 18) said
proppant has a high whisker distribution density based on
individual whiskers present in the proppant (# of whiskers per mg
of proppant); [0424] 19) said proppant has a unimodal whisker
distribution; [0425] 20) said proppant has at least two layers that
form a laminate structure; [0426] 21) said proppant has at least a
first layer and a second layer that form a laminate structure
wherein the average length of said whiskers in said first layer
compared to said second layer is different; [0427] 22) said
proppant has at least a first layer and a second layer that form a
laminate structure wherein the average width of said whiskers in
said first layer compared to said second layer is different; [0428]
23) said whiskers in said proppant are less euhedral and more
anhedral; [0429] 24) said proppant has at least one radial region
of first whiskers and at least one region of second whiskers,
wherein the average whisker length is different by at least 10%;
[0430] 25) said proppant has at least one radial region of first
whiskers and at least one region of second whiskers, wherein the
average whisker width is different by at least 10%; [0431] 26) said
proppant has a major phase of whiskers of less than one micron and
a secondary minor phase of whiskers of one micron or higher; and/or
[0432] 27) said ceramic whiskers have a whisker length distribution
having d.sub.a90, which is a whisker length wherein 90% of the
whiskers have a smaller whisker length, of less than 12 microns.
[0433] 140. The proppant of any preceding or following
embodiment/feature/aspect, wherein one or more of said
characteristics provide stress reducing properties on said proppant
compared to the same proppant but without said characteristics.
[0434] 141. The proppant of any preceding or following
embodiment/feature/aspect, wherein said proppant has an alumina
content of at least 35% by weight of said proppant. [0435] 142. The
proppant of any preceding or following embodiment/feature/aspect,
wherein said mullite whiskers are present in an amount of from 10%
to 40% by weight of said proppant. [0436] 143. The proppant of any
preceding or following embodiment/feature/aspect, further
comprising quartz. [0437] 144. The proppant of any preceding or
following embodiment/feature/aspect, further comprising quartz in
an amount of from 0.1 wt % to 1 wt % based on the weight of the
proppant. [0438] 145. The proppant of any preceding or following
embodiment/feature/aspect, wherein said proppant comprises at least
one layered shell encapsulating a hollow spherical template. [0439]
146. The proppant of any preceding or following
embodiment/feature/aspect, wherein said proppant comprises at least
one layered shell encapsulating a hollow spherical template, and
said nano-microspheres are present in said at least layered
shell.
[0440] The present invention can include any combination of these
various features or embodiments above anchor below as set forth in
sentences anchor paragraphs. Any combination of disclosed features
herein is considered part of the present invention and no
limitation is intended with respect to combinable features.
[0441] The present invention will be further clarified by the
following examples, which are intended to be exemplary of the
present invention.
EXAMPLES
Example 1
[0442] Raw, unexpanded perlite powder (Grade #270, Hess Pumice
Products, 100 Hess Dr. Malad City, Id. 83252) with initial particle
size of 595 .mu.m (-30 mesh) was attrition-milled to reach on
average particle size of around 0.5 .mu.m and then mixed with
cenospheres (Grade Sphere One SG Temperate, 8020 Tyler Blvd, Suite
#100, Kish Company Inc. Mentor, Ohio 44060) and alumina (Grade
AC-300 Ungrounded, Aluchem, 14782 Beaver Pike, Jackson, Ohio 45640)
in deionized water. The mixture was ball-milled with high purity
alumina media for 4 hours. Before blending with the perlite, the
cenosphere and alumina powders were also attrition-milled down to
an average particle size of around 0.5 .mu.m. The mixed slurry was
then dried in an oven at 125.degree. C. for 4-8 hours and the dry
powder was sieved through a 120 mesh screen. Pellets of
approximately 0.5''.times.0.2'' were uniaxially pressed at 12 MPa
and sintered at 1175.degree. C.-1250.degree. C. from 2 hours to 6
hours in air. After the firing, the pellets were cleaned.
[0443] Split tensile strength was determined by ASTM C 1144-89,
"Standard Test Method for Splitting Tensile Strength for Brittle
Nuclear Waste Forms." From FIG. 5, it can be seen that a
significant increase in strength was achieved as the initial
concentration of perlite was increased. Only a slight increase in
specific gravity was observed with increasing perlite
concentration. Maximum crush strength was achieved near a
composition of 50 wt % Al.sub.2O.sub.3, 30 wt % Cenoshperes, and 20
wt % Perlite. Reduction in crush strength occurs when the
concentration of perlite was increased or decreased from
approximately 20 wt %. The possible reasons for improvement in
strength may involve (1) reduction in the numbers of pores and
sizes of pores without too much increase in specific gravity; (2)
smooth pore surfaces and outer surface of the proppant produced by
the fused perlite leading to release of stress concentrations at
the surface of the pores and the surface of the proppant; and/or
(3) optimization in phase constitution (optimization in phase
percentages among mullite, alumina and amorphous phases).
[0444] X-ray diffraction (phase analysis) was conducted using X-ray
diffractometer Siemens D5000. Microstructure. Observations were
performed using VEGA-II Scanning Electron Microscopes (Tescan USA
Inc. 508 Thomson Park Drive, Cranberry Twp, Pa. 16066). FIG. 6
shows the X-ray diffraction pattern from a sintered pellet where
the green body composition was approximately 50 wt %
Al.sub.2O.sub.3, 30 wt % Cenospheres, 20 wt % Perlite. Corundum
(.alpha.-Alumina), mullite, and the amorphous material are the
major phases identified in the sintered pellet. The material
comprising the wall of a cenosphere had a specific gravity of about
2.65. Unexpanded perlite has a specific gravity of about 2.2. The
inclusion of proportionately more perlite relative to cenospheres
will reduce the average specific gravity of the proppant. The
inclusion of proportionately more perlite relative to cenospheres
reduces the number and size of pores produced which tends to
increase the average specific gravity of the proppant. The net
effect is relatively little change in average specific gravity with
an accompanying significant increase in crush strength. This is an
unexpected and useful result, improving the balance of crush
strength and specific gravity in the proppant. FIG. 7 shows a
comparison of various alumina, silica, perlite composites including
formulations with no perlite. The compositions containing perlite
show an improved balance of specific gravity and crush strength. In
FIG. 7, A2, A14, A16SG, A1000, AC2, and AKP50 are grade names of
alumina from different vendors. SiC, B4C and PMMA are additives to
the standard alumina-cenosphere composition.
[0445] FIG. 8 is an image produced from a scanning electron
microscope at magnification 5.0 kx showing pores in a proppant
produced with the composition: 50 wt % Al.sub.2O.sub.3, 30 wt %
Cenospheres, 20 wt % Perlite. FIG. 9 is an image produced from a
scanning electron microscope at magnification 10.0 kx showing pores
in a sintered pellet, where the green body composition was
approximately 50 wt % Al.sub.2O.sub.3, 30 wt % Cenospheres. The
pores in FIG. 8 (50 wt % Al.sub.2O.sub.3, 30 wt % Cenospheres, and
20 wt % Perlite) are smaller in number and size when compared to
the pores in FIG. 9 (50 wt % Al.sub.2O.sub.3 and 30 wt %
Cenospheres), demonstrating one of the benefits of incorporating
perlite in the proppant formulation.
[0446] Applicants specifically incorporate the entire contents of
all cited references in this disclosure. Further, when an amount,
concentration, or other value or parameter is given as either a
range, preferred range, or a list of upper preferable values and
lower preferable values, this is to be understood as specifically
disclosing all ranges formed from any pair of any upper range limit
or preferred value and any lower range limit or preferred value,
regardless of whether ranges are separately disclosed. Where a
range of numerical values is recited herein, unless otherwise
stated, the range is intended to include the endpoints thereof, and
all integers and fractions within the range. It is not intended
that the scope of the invention be limited to the specific values
recited when defining a range.
[0447] Other embodiments of the present invention will be apparent
to those skilled in the art from consideration of the present
specification and practice of the present invention disclosed
herein. It is intended that the present specification and examples
be considered as exemplary only with a true scope and spirit of the
invention being indicated by the following claims and equivalents
thereof.
* * * * *