U.S. patent application number 09/955281 was filed with the patent office on 2002-05-16 for proppant composition for gas and oil well l fracturing.
This patent application is currently assigned to Fairmount Minerals, Ltd. Invention is credited to Akbar, Syed, Okell, Patrick R., Youngman, Robert.
Application Number | 20020058581 09/955281 |
Document ID | / |
Family ID | 26929640 |
Filed Date | 2002-05-16 |
United States Patent
Application |
20020058581 |
Kind Code |
A1 |
Youngman, Robert ; et
al. |
May 16, 2002 |
PROPPANT COMPOSITION FOR GAS AND OIL WELL L FRACTURING
Abstract
An aluminosilicate ceramic, spherical pellet made from spent
ceramic catalyst. More specifically, a spherical ceramic pellet
made from spent fluid cracking catalyst. The pellets can be made by
grinding the catalyst particles, forming them into spherical
pellets, and then sintering the pellets. The final product is
useful as a proppant in oil and gas well fracturing.
Inventors: |
Youngman, Robert; (Phoenix,
AZ) ; Okell, Patrick R.; (Bellaire, TX) ;
Akbar, Syed; (Pearland, TX) |
Correspondence
Address: |
JOSEPH G CURATOLO, ESQ.
RENNER KENNER GREIVE BOBAK TAYLOR & WEBER
24500 CENTER RIDGE ROAD, SUITE 280
WESTLAKE
OH
44145
US
|
Assignee: |
Fairmount Minerals, Ltd
P.O. Box 87
Chardon
OH
44024
|
Family ID: |
26929640 |
Appl. No.: |
09/955281 |
Filed: |
September 18, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60236292 |
Sep 28, 2000 |
|
|
|
Current U.S.
Class: |
501/155 |
Current CPC
Class: |
C04B 41/52 20130101;
C04B 41/52 20130101; C04B 41/4584 20130101; C04B 41/52 20130101;
C09K 8/805 20130101; C09K 8/80 20130101; C04B 41/009 20130101; C04B
41/4811 20130101; C04B 41/4823 20130101; C04B 41/52 20130101; C04B
35/18 20130101; C04B 41/4584 20130101; Y10T 428/2998 20150115; C04B
35/622 20130101; C04B 41/009 20130101; C04B 35/18 20130101 |
Class at
Publication: |
501/155 |
International
Class: |
C04B 035/00 |
Claims
What is claimed is:
1. A spherical ceramic proppant pellet comprising spent fluid
cracking catalyst particles, wherein the pellet is formed by: a.
reducing the median particle size of the catalyst; b. mixing the
catalyst particles with water and a binder to form spherical
pellets; and c. sintering the pellets.
2. The proppant pellet of claim 1, wherein the pellet has a
Krumbein roundness and sphericity of greater than or equal to
0.9.
3. The proppant pellet of claim 1, wherein the pellet has a crush
strength at 7,500 psi of less than or equal to 9.1 percent.
4. The proppant pellet of claim 1, wherein the pellet has a
conductivity at least about 1650 md-ft, after 50 hours at 10,000
psi and 250.degree. F. using 2% KCl as the flowing medium.
5. The proppant pellet of claim 1, wherein the spent fluid cracking
catalyst comprises from about 25 to about 80 weight percent silica,
and from about 20 to about 75 weight percent alumina.
6. The proppant pellet of claim 1, wherein the pellet comprises
silica and alumina in a weight ratio of about 2:1 to about 1:1.
7. The proppant pellet of claim 1, wherein the pellet comprises
silica and alumina in a weight ratio of about 1:1.
8. The proppant pellet of claim 1, wherein the spent fluid cracking
catalyst comprises a zeolite.
9. The proppant pellet of claim 1, wherein the density of the
pellets after sintering is from about 2 g/cm.sup.3 to about 2.7
g/cm.sup.3.
10. The proppant pellet of claim 1, wherein the pellet is coated
with at least one resin.
11. A method for preparing a spherical ceramic proppant pellet, the
method comprising: a. providing spent fluid cracking catalyst
particles; b. reducing the particle size of the catalyst particles;
c. mixing the catalyst particles with water and a binder to form
spherical pellets; and d. sintering the pellets.
12. The method of claim 11, wherein said reducing the particle size
of the catalyst particles comprises reducing the mean particle size
of the particles to from about 4 to about 6 microns.
13. The method of claim 11, wherein the binder is one of polyvinyl
acetate, methyl cellulose, and polymethylmethacrylate.
14. The method of claim 11, wherein said sintering comprises
heating the pellets at a temperature of between about 1,300.degree.
C. to about 1,500.degree. C.
15. The method of claim 11, wherein the method further comprises
coating the pellets with at least one resin after sintering.
16. The method of claim 15, wherein said coating comprises coating
the pellet with an inner coating of a fusible, curable resin and an
outer coating of a substantially cured resin.
17. The method of claim 15, wherein said coating comprises coating
the pellet with a substantially cured inner resin coating, an outer
resin coating, wherein the outer resin coating may be cured or
curable, and optionally a reinforcing agent.
18. The method of claim 11, wherein the spent fluid cracking
catalyst particles comprise a zeolite.
19. The method of claim 11, further comprising screening the
pellets to a mean particle size of 20/40 mesh.
20. A proppant pellet composition comprising pelletized and
calcined spent fluid cracking catalyst, wherein the spent fluid
cracking catalyst comprises from about 25 to about 80 weight
percent silica, and from about 20 to about 75 weight percent
alumina.
21. The proppant pellet composition of claim 20, wherein the silica
and alumina are present in a weight ratio of silica/alumina of from
about 2:1 to about 1:1.
22. The proppant pellet composition of claim 20, wherein the silica
and alumina are present in a weight ratio of silica/alumina of
about 1:1.
23. The proppant pellet composition of claim 20, wherein the
density of the pellet composition after sintering is from about 2
g/cm.sup.3 to about 2.7 g/cm.sup.3.
24. The proppant pellet composition of claim 20, wherein the mean
particle size of the pellet composition is about 20/40 mesh.
25. The proppant pellet composition of claim 20, wherein the spent
fluid cracking catalyst optionally further comprises at least one
of: up to about 1000 parts per million copper; up to about 7000
parts per million vanadium; up to about 200 parts per million lead;
up to about 7000 parts per million nickel; up to about 2500 parts
per million antimony; up to about 2 weight percent iron; up to
about 1.5 weight percent sodium; and, detectable amounts of at
least one component selected from the group consisting of platinum,
rhenium, sulfur compounds, and rare earth metals.
26. The proppant pellet composition of claim 20, wherein the
composition further comprises at least one resin coating.
27. The proppant pellet composition of claim 25, wherein the resin
coating comprises an inner coating of a substantially cured resin,
an outer coating of resin, and optionally a reinforcing agent
interspersed at the inner coating/outer coating boundary.
28. The proppant pellet composition of claim 25, wherein the resin
coating comprises an inner coating of a fusible curable resin and
an outer coating of a substantially heat-cured resin, wherein the
resin of the outer coating is heat-curable at conditions that leave
the resin of the inner coating uncured.
29. The proppant pellet composition of claims 27 or 28, wherein the
resin of the inner coating is at least one resin independently
selected from the group consisting of phenol-aldehyde resins,
urea-aldehyde resins, melamine-aldehyde resins, epoxy resins,
furfuryl alcohol resins, and copolymers of such resins; and wherein
the resin of the outer coating is at least one resin independently
selected from the group consisting of phenol-aldehyde resins,
urea-aldehyde resins, melamine-aldehyde resins, epoxy resins,
furfuryl alcohol resins, and copolymers of such resins.
30. A method of propping a fracture in a subterranean formation
comprising creating a fracture in said subterranean formation, and
placing in said fracture a quantity of the proppant pellets set
forth in any one of the above claims.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to proppant pellets prepared
by using aluminasilica containing waste materials from industrial
processes. The proppant pellets may be resin coated. The present
invention further relates to a method for the manufacture of
proppant pellets.
BACKGROUND OF THE INVENTION
[0002] In the completion and operation of oil wells, gas wells,
water wells, and similar boreholes, it frequently is desirable to
alter the producing characteristics of the formation by treating
the well. Many such treatments involve the use of particulate
material. For example, in hydraulic fracturing, particles called
proppants are used to maintain the fracture in a propped condition.
In hydraulic fracturing, proppant particles under high closure
stress tend to fragment and disintegrate. At closure stresses above
about 5,000 psi, silica sand, the most common proppant, is not
normally employed due to its propensity to disintegrate. The
resulting fines from this disintegration migrate and plug the
interstitial flow passages in the propped interval. These migratory
fines drastically reduce the permeability of the propped fracture.
Since closure stress varies directly with depth, this means that
sand is not a useful proppant material at depths greater than about
5,000 feet.
[0003] Sintered bauxite or high grade alumina have been used as
proppant materials at well depths greater than 20,000 feet, but
these high strength proppants have much higher densities than sand
and therefore require high viscosity pumping fluids or high pumping
rates. Larger pumping equipment is required, and wear rates on
fluid carrying equipment is accelerated. In addition, the raw
materials used to make the proppant materials are more costly.
[0004] Proppants of intermediate density are known, and work well
in the intermediate depths and pressures, i.e., 7,000 to 14,000
feet (5,000-10,000 psi). Proppant pellets having a specific gravity
of less than 3.4 g/cm.sup.3 have been made from diaspore clay,
bauxite, and/or alumina. Eufala bauxite, a bauxitic-kaolin
material, has been used to prepare a proppant with a density of
less than 3.0 g/cm.sup.3. Also known is a method of making ceramic
microspheres for use as proppants from water-soluble salts, mineral
compositions or organometallic complexes, and ultrafine bauxite or
alumina-containing particles. A low density proppant has been
prepared from kaolin clay and amorphous to microcrystalline silica.
The raw materials used to make all these intermediate proppants are
costly, and a less expensive proppant material is desired.
[0005] Resin coated particles have been used in efforts to improve
the stability of proppants at high closure stresses. Sand or other
substrates have been coated with an infusible resin such as an
epoxy or phenolic resin. These materials are superior to sand at
intermediate stress levels. However, at high temperature and high
stress levels, the resin coated particles still show a decrease in
permeability.
[0006] A process is known for coating particulates with an
infusible resin for use as proppants in fracturing operations. The
particulates include sand, nut shells, glass beads and aluminum
pellets. The resins include urea-aldehyde resins, phenol-aldehyde
resins, epoxy resins, furfuryl alcohol resins and polyester or
alkyd resins. The resin coating may be applied by mixing the
particles with a melted resin and subsequently cooling the mixture,
or dissolving the resin in a solvent, applying it to the particles,
and evaporating the solvent. Coupling agents may be added to the
system to improve the strength of the resin-substrate bond.
[0007] Proppants comprising sand particles with a precured phenol
formaldehyde resin coating have been used for propping fractures in
subterranean formations.
[0008] Although resin coated sands have proven satisfactory in
numerous applications, concern exists over their use under high
closure stresses. For example, some self consolidating resin coated
particles of the prior art do not develop their full strength until
the resin coating has cured in the formation. In the event of rapid
closure of the fracture, the proppant could be crushed before the
resin cured, resulting in decreased permeability. This problem is
alleviated by the use of a dual resin coated particle having a
reinforcing agent interspersed at the inner resin/outer resin
boundary, as described in U.S. Pat. No. 5,422,183 assigned to
Santrol, Inc, incorporated herein by reference as if fully written
out below.
SUMMARY OF THE INVENTION
[0009] The present invention utilizes spent ceramic media from
petroleum refining operations, where the media provides a catalytic
function during "cracking" of the hydrocarbons, while drawing out
impurities from the crude oil as it passes through a packed column
of ceramic beads. These beads are manufactured by Englehard
Corporation, WR Grace and Akzo Nobel as well as other Far Eastern
producers and are variously known as fluid cracking catalyst,
e-cats, and equilibrium catalyst (hereinafter referred to as "fluid
cracking catalyst" or "FCC"). The use of catalytic ceramic media
for removing impurities from petroleum products is a long
established art. The catalytic media can be regenerated after use
as a cracking catalyst several times but eventually is spent, and
is discarded as waste material. The present invention uses the FCC
as a base material for remanufacturing larger ceramic spheres,
which can be used in the hydraulic fracturing of subterranean oil
and gas bearing formations.
[0010] The present invention provides a spherical ceramic proppant
pellet comprising spent fluid cracking catalyst particles, wherein
the pellet is formed by reducing the median particle size of the
catalyst; mixing the catalyst particles with water and a binder to
form spherical pellets; and sintering the pellets.
[0011] The present invention also provides a method for preparing a
spherical ceramic proppant pellet, the method comprising the steps
of providing spent fluid cracking catalyst particles; reducing the
particle size of the catalyst particles; mixing the catalyst
particles with water and a binder to form spherical pellets; and
sintering the pellets.
[0012] The present invention further provides a proppant
composition comprising spent fluid cracking catalyst, wherein the
spent fluid cracking catalyst comprises from about 25 to about 80
weight percent synthetic silica, and from about 20 to about 75
weight percent alumina. The spent fluid cracking catalyst may
optionally further comprise at least one of:
[0013] up to about 1,000 parts per million copper;
[0014] up to about 7,000 parts per million vanadium;
[0015] up to about 200 parts per million lead;
[0016] up to about 7000 parts per million nickel;
[0017] up to about 2500 parts per million antimony;
[0018] up to about 2 weight percent iron;
[0019] up to about 1.5 weight percent sodium; and,
[0020] detectable amounts of a least one component selected from
the group consisting of platinum, rhenium, sulfur compounds, and
rare earth metals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a graphical representation of the conductivity of
an FCC ceramic proppant and a commercial lightweight ceramic
proppant at various closure pressures.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The present invention utilizes fluid cracking catalyst, a
material rich in alumina and silica, as a ceramic feedstock for
producing proppant pellets. The catalyst material is formed into
pellets and sintered using conventional methods.
[0023] Spent fluid cracking catalysts exist as ceramic beads
comprising calcined mixtures of silica (SiO2), alumina (Al2O3),
with minor amounts of antimony, copper, nickel, vanadium, lead,
rare earth metals, sulfates, sulfides, and trace amounts of other
components. Although the exact compositions of commercial FCCs are
proprietary, in general a fluid cracking catalyst has four major
component systems: zeolite, matrix, binder, and filler.
[0024] Zeolite, sometimes called molecular sieve, has a
well-defined lattice structure. Its basic building blocks are
silica and alumina tetrahedra. Typical zeolites also contain
counterions such as sodium, and ammonium ions. Zeolites employed in
the manufacture of the FCC catalyst are synthetic versions of
naturally occurring zeolites called faujasites. Zeolites with
applications to FCC are Type X, Type Y, and ZSM-5. Both X and Y
zeolites have essentially the same crystalline structure. The major
difference is that the X zeolite has a lower silica/alumina ratio
than the Y zeolite. Virtually all of today's catalysts contain Y
zeolite or variations thereof. One variation is an
aluminum-deficient zeolite, called ultrastable Y, or simply USY.
Zeolites are sometimes ion exchanged with rare earth components in
order to increase catalytic activity and thermal stability. Rare
earth is a generic name for fourteen metallic elements of the
lanthanide series, including lanthanum and cerium.
[0025] The matrix component of the FCC can also have catalytic
activity. Alumina is normally the source for the matrix component.
Most FCCs contain an amorphous alumina matrix, but some catalyst
suppliers incorporate a form of alumina that has a crystalline
structure.
[0026] The filler component is a clay incorporated into the
catalyst to dilute its activity. Kaolin
[Al.sub.2(OH).sub.2,Si.sub.2O.sub.5] is the most common clay used
in the FCC catalyst. One FCC catalyst manufacturer used kaoline
clay as a skeleton to grow the zeolite in situ.
[0027] The binder serves as a "glue" to hold the zeolite, matrix
and filler together. The functions of the filler and the binder are
to provide physical integrity and mechanical strength. They impact
such characteristics of the FCC as density, attrition resistance,
and particle size distribution.
[0028] Spent fluid cracking catalyst also contains a number of
metal contaminants, including nickel, vanadium, iron, antimony and
copper. These contaminants originate largely from the heavy,
high-molecular weight fraction of the FCC feed. The quantity of
these metals on the FCC is determined by their levels in the
petroleum feedstock and the catalyst addition rate. Essentially,
all these metals in the feed are deposited on the catalyst. Much of
the iron on the FCC comes from metal scale from piping.
[0029] Another component of spent fluid cracking catalyst is coke,
which is carbon that is deposited on the catalyst during
cracking.
[0030] As metal and carbon contaminants are deposited on the FCC,
the catalyst loses its activity and selectivity. Fresh catalyst is
added to the reactor unit continually to replace the catalyst lost
by attrition and to maintain catalyst activity. In cases where the
makeup rate for activity maintenance exceeds catalyst losses, part
of the catalyst inventory is periodically withdrawn from the unit
to control the catalyst level in the regenerator. This spent
catalyst provides a low cost feedstock that is rich in alumina and
silica, and according to the invention is remanufactured to produce
larger ceramic spheres. The ceramic spheres can be used as
proppants in the hydraulic fracturing of subterranean oil and gas
bearing formations.
[0031] Spent fluid cracking catalysts suitable for the proppant of
the present invention therefore primarily contain silica and
alumina, and may further contain sodium or other counterions, rare
earth elements, carbon, metals such as typically found in petroleum
feedstocks, and other contaminants.
[0032] The ratio of silica to alumina is a critical factor in the
ultimate performance of the proppant product, but can be quite
variable in fluid cracking catalysts. A nominal 45/55 silica to
alumina weight ratio is quite common in FCCs. Preferred useful
ratios by weight of silica to alumina for use as a feedstock
material for proppants according to the present invention are about
2:1 to more preferably about 1:1. Spent fluid cracking catalyst
suitable for use as a feedstock material comprise 25-80 weight
percent silica, preferably 40 to 60, weight percent silica, and
even more preferably 45 to 55 weight percent silica. Suitable fluid
cracking catalyst for use according to the present invention
comprise 20-75 weight percent alumina, preferably 30 to 60 weight
percent alumina, and even more preferably 45 to 55 weight percent
alumina. Typical ranges of chemical compositions for MET 192 or MET
195 from Metalloy Corporation are shown in Table A.
1 TABLE A Chemical Name Wt Percent Silica (synthetic), SiO.sub.2
25-80 Alumina Al.sub.2O.sub.3 20-75 Quartz (SiO.sub.2) <1.0
Antimony 0-2500 ppm Copper 5-1000 ppm Vanadium 45-7000 ppm Lead 200
ppm
[0033] This chemical analysis is included for example purposes
only, and should not be considered as a limitation of the FCC used
to produce the proppants of the present invention. In some
instances, alumina or silica can be added, such as clay or silica
gel, to adjust the silica:alumina weight ratio to 1:1 to 2:1.
[0034] The spherical ceramic proppant pellets of the present
invention are prepared by a method comprising the steps of
providing spent fluid cracking catalyst particles, reducing the
particle size of the catalyst particles, mixing the catalyst
particles with water and a binder to form spherical pellets, and
sintering the pellets. The pellets are preferably screened to
provide a suitable median particle size.
[0035] Reduction of the particle size of the FCC particles is
preferably accomplished by conventional ball milling techniques,
including either wet or dry ball milling. The median particle size
of the FCC particles after reduction is preferably about 1 to about
10 microns, and more preferably about 2 to about 6 microns, as
measured by laser diffraction.
[0036] The comminuted FCC particles are then mixed with water and a
binder. Suitable binders include, but are not limited to, polyvinyl
acetate, methyl cellulose, and polymethylmethacrylate. The amount
of water used is preferably 25-45 percent by weight of fluid
cracking catalyst, but will vary depending on the composition of
the FCC. The amount of binder used is preferably about 0.1% to 0.5%
by weight, preferably about 0.2 to 0.25%, but will depend on
particle size distribution and shape.
[0037] Mixing may be accomplished by conventional methods.
Preferably, a Eirich mixer is used, such as an Eirich RVO2. The
pellet size is determined by mixer run time. A mix time of 45
seconds to 80 seconds is usually sufficient in the particular
equipment used to form well rounded substantially spherical pellets
in the size range of 1 mm to 420 microns. After spherical pellets
form, the pellets are dried at relatively low temperatures of from
about 120 to about 150.degree. C. After drying, the pellets are
sufficiently tough to undergo the stress of pneumatic handling and
sintering.
[0038] Sintering is preferably accomplished using a rotary kiln,
although other conventional sintering methods may be used. Pellets
are sintered at a temperature of about 1,300.degree. C. to about
1,500.degree. C. The temperature along the kiln will vary but most
preferably a temperature of about 1,500.degree. C. is attained for
a dwell time of at least about 30 minutes. Sintering causes a
reduction of up to 20% in particle size as well as an increase in
density in the component products. A finished proppant particle
according to the process described above may have a density in the
range of about 2 to about 2.7 gm/cm.sup.3, depending upon the
source FCC and actual sintering temperature. Preferably, the
density of the finished proppant particle is from about 2.45
gm/cm.sup.3 to about 2.65 gm/cm.sup.3.
[0039] After sintering the pellets assume a darker gray color and
can be screened by Rotex or other conventional methods into the
particle sizes needed. A typical product size is 20/40 mesh, which
indicates that 90 weight percent of its pellets are between 0.0167
inches and 0.0331 inches in size. Preferably, 90 weight percent of
the pellets are between 0.0232 inches and 0.0331 inches in
size.
EXAMPLE 1
[0040] Spent FCC particles were ball milled to a 4-6 micron median
particle size, as measured by laser diffraction. Ten pounds of
milled material having a dried, free flowing form was fed to a
pellet forming mixer device, specifically an Eirich RVO2. To the
test batch, 25% to 45% by weight of water and liquid polyvinyl
acetate (PVA) was added in the amount of 0.3% by liquid volume. The
addition of PVA added green strength for subsequent sintering.
[0041] When spherical pellets formed in the mixer, the machine was
stopped and the pellets were transferred to a low temperature
convection oven and dried at 120.degree. F. for 1 hour. The
specific gravity of the product at this stage was approximately 2.1
gm/cm.sup.3.
[0042] After drying, the spherical pellets were sintered in a
rotary kiln at a temperature of between 1,325.degree. C. to
1,500.degree. C. for about 30 minutes. After sintering, the pellets
were screened to 20/40 mesh.
[0043] The pellets so formed are surprisingly similar in
performance to existing ceramic proppant pellets, albeit with
slightly lower crush resistance and lower conductivity with respect
to brine and hydrocarbons, as shown in FIG. 1.
Conductivity Data
[0044] Conductivity testing to determine the relative conductivity
of the final FCC pellets was followed according to standard StimLab
procedures using 2% KCl as the flowing medium. As shown in Table 1,
the data indicate that the FCC product, although slightly lower in
absolute conductivity, is within 10% of the performance of a
typical lightweight ceramic at higher closures (10,000 psi). This
is graphically represented in FIG. 1, where line 10 shows the
performance of commercial lightweight ceramic proppant, and line 20
show the performance of the FCC ceramic proppant.
2TABLE 1 Conductivity of 20/40 FCC Ceramic Proppant vs. Commercial
20/40 Lightweight Ceramic Proppant 2 lb./sq.ft., 250.degree. F., 50
hours @ closure, 2% KCl solution. Conductivity (md-ft) Conductivity
Closure Lightweight (md-ft) (psi) Ceramic Proppant FCC Ceramic
Proppant 1000 10518 10278 2000 8800 7365 4000 8157 6500 6000 6100
5100 8000 4738 3719 10000 1973 1770
Crush Data
[0045] Crush numbers were generated at 7,500 psi, according to
standard API RP 60 procedures. Crush data, shown in Table 2,
indicate a slight decline in crush strength over current
lightweight ceramics, but the proppants prepared according to the
present invention have performance approximating existing
commercial proppant products, and are suitable for commercial
use.
3 TABLE 2 20/40 Proppant Material % Crush at 7500 psi FCC Ceramic
Proppants 9.1 Commercial Lightweight 6.8 Ceramic Proppants
[0046] It is expected that crush resistance and conductivity of the
proppant products prepared according to the present invention, will
equal or exceed that of commercial lightweight ceramic proppants,
with manufacturing scaleup.
Roundness and Sphericity
[0047] The Krumbein roundness and sphericity of the FCC derived
ceramic proppants are approximately 0.9 and are equivalent to
commercial lightweight ceramic proppants.
[0048] Additional proppant pellets were prepared from spent FCC
catalyst according to the above described procedure, with 24 hour
wet milling in a ball mill, drying and pressing into pellets.
Sintering was conducted at 1300.degree. C., 1400.degree. C. or
1500.degree. C. for 10 minutes. A final density of 99.6% of
theoretical was achieved. X-ray diffraction indicated that the
pellets contained about 50 to about 60 mol % cristobalite and about
40 to about 50 mol % mullite.
[0049] Other proppant pellets prepared according to the process of
the present invention were tested for conductivity as described
above, and the results of the tests are reported in Table 3,
below.
4 TABLE 3 Closure Conductivity (psi) (md-ft) 1000 8750-10278 2000
6500-7365 4000 5500-6500 6000 4800-5100 8000 3500-3719 10000
1650-1770
[0050] Advantageously, proppant pellets comprising spent fluid
cracking catalyst utilize waste materials from the petroleum
refining process which would otherwise be costly to dispose of or
reclaim. The proppant pellets of the present invention are
lightweight, low density materials with crush strength and
conductivity approximating those of existing products.
[0051] The utility of the FCC ceramic proppant of the present
invention can be extended into high stress applications by coating
the proppant with a resin coating. The resin coating may be cured
or curable. In one embodiment, the FCC ceramic proppant pellets are
coated with a resin dissolved in a solvent which is then
evaporated. The resin is then cured. In another embodiment, the FCC
ceramic proppant pellets are mixed with a melted resin which is
then cooled, coating the pellets. The resin coating is then cured.
Alternately, the resin coating is curable, but not substantially
cured prior to use. In this embodiment, the resin is cured after
injection into the well formation by techniques known in the
art.
[0052] In a preferred embodiment, FCC ceramic proppant pellets are
covered with an inner coating of a fusible, curable resin and an
outer coating of a substantially cured resin. The resin coated
particle can be used as a self-consolidating proppant, and is
compatible with the fracturing fluid. If desired, the proppant
pellet may further comprise an additional coating of a
substantially cured resin which is located on the exterior of the
substrate and inside the inner coating. Such particles exhibit
enhanced properties such as improved fractionating fluid
compatibility.
[0053] Resins suitable for the inner and outer coatings are
generally any resins capable of being coated on the substrate and
then being cured to a higher degree of polymerization. Examples of
such resins include phenol-aldehyde resins of both the resole and
novolac type, urea-aldehyde resins, melamine-aldehyde resins, epoxy
resins and furfuryl alcohol resins and copolymers of such resins.
The resins must form a solid non-tacky coating at ambient
temperatures. This is required so that the coated particles remain
free flowing and so that they do not agglomerate under normal
storage conditions.
[0054] The preferred resins are the phenol-formaldehyde resins.
These resins include true thermosetting phenolic resins of the
resole type and phenolic novolac resins that may be rendered heat
reactive by the addition of catalyst and formaldehyde. Such resins
with softening points of 185.degree. F. to 290.degree. F. are
acceptable.
[0055] The inner and outer coatings can be formed starting with the
same or different type of resins. For example, the inner coating
could be produced from a novolac and the outer coat from a resole.
Regardless of the type of resin used, the outer resin must be
curable at conditions that leave the inner coating curable, i.e.,
fusible and heat reactive.
[0056] A coupling agent as subsequently described is preferably
incorporated during manufacture into the resin that is to be used
as the inner coating, and may optionally also be incorporated into
the resin that is to be used as the outer coating. The coupling
agent which has a functional group reactive in the resin system is
added in an amount ranging from about 0.1 to 10% by weight of the
resin. The preferred range is from about 0.1 to 3% by weight of the
resin. When using the preferred phenol formaldehyde resins, the
coupling agent is incorporated into the resin under the normal
reaction conditions used for the formation of the
phenol-formaldehyde resin. The coupling agent is added to the resin
after the phenol formaldehyde condensation reaction has occurred
and the resin has been dehydrated to the final free phenol and melt
viscosity range.
[0057] A preferred resin of the inner coating is a phenolic novolac
resin. Particularly suitable are phenolic novolac resins
manufactured by Georgia Pacific, known as 99NO7, and by OxyChem,
known as 24-715. The GP-099N07 resin has a softening point range of
85.degree. F.-100.degree. F. The OxyChem 24-715 exhibits a
softening point range of 70.degree. F.-87.degree. F. When either
resin is used, it is necessary to add to the mixture a
cross-linking agent to effect the subsequent curing of the resin.
Hexamethylenetetramine is the preferred material for this function
as it serves as both a catalyst and a source of formaldehyde.
[0058] The coupling agent to be employed is chosen based on the
resin to be used. For phenolic resins, the coupling agents include
amino, epoxy, and ureido organo silanes. Epoxy modified
gamma-glycidoxypropyltrimethoxy- silane has given excellent results
when used in the amount of 0.50-1.00% based on the weight of the
resin. The use of coupling agents as incorporated into the resin
and as applied directly to the particulate substrate is discussed
in Graham et al, U.S. Pat. No. 4,518,039, incorporated herein by
reference as if fully written out below.
[0059] The outer coating of resin is formed from a heat curable
resin coating formed over the inner resin. As stated previously,
this outer resin must be curable at conditions that do not
completely cure the inner coating thus leaving the inner coating
curable. The preferred resins for the outer coating are of the
resole type. Particularly suitable is a fast curing resole resin
manufactured by Georgia Pacific known as 102N68. Resole resins
generally are provided dissolved in a methanol and water solution
as is Georgia Pacific 102N68. The resin exhibits an extremely fast
cure having a 150.degree. C. hot plate cure time of 30 seconds or
less. The preferred resole should be in a solution of water and
methanol as the solvent system. The organic solids level should be
65-75%, with a water content in the 5-15% level. The hot plate cure
time at 150.degree. C. should be in the range of 25-40 seconds.
[0060] The inner and outer resin coatings may be formed by a
variety of methods. For example, the solvent coating process
described in U.S. Pat. No. 3,929,191, to Graham et al.,
incorporated herein by reference as if fully written out below.
[0061] Other processes such as that described in U.S. Pat. No.
3,492,147 to Young et al. describes the coating of a particulate
substrate with a liquid, uncatalyzed resin composition
characterized by its ability to extract a catalyst or curing agent
from a non-aqueous solution. As stated above, the preferred resins
for use with the instant invention are phenol-formaldehyde novolac
resins. When using such resins the preferred coating method is a
hot melt coating procedure for forming the inner coat. Such a
procedure is described in U.S. Pat. No. 4,585,064, to Graham et al,
incorporated herein by reference as if fully written out below.
Solvents are preferably used to apply the outer coat. The following
is a discussion of typical coating process parameters using the
preferred phenol-formaldehyde novolac resins.
[0062] The improved high strength particles of this embodiment of
the invention are coated in a multi-step process. In the first step
a phenol-formaldehyde resin inner coat is formed over the
particulate substrate. In the second step an outer coating is
formed. The outer coating is then cured at conditions that leave
the inner resin curable.
[0063] The first or inner coating of resin may be formed on the
particulate substrate by first coating the heated substrate with a
phenol-formaldehyde novolac resin. This coating is carried out by
preheating the particulate substrate to a temperature above the
melting point of the particular resin used.
[0064] Typically the particulate substrate is heated to 350.degree.
F. to 500.degree. F. prior to resin addition. The heated substrate
is charged to a mixer or muller where generally from about 1% to
about 6%, by weight of substrate, resin is added. The preferred
amount of resin based on the weight of substrate is about 2%.
[0065] After completion of addition of the resin to the substrate,
the substrate and melted resin are allowed to mix in the muller for
a time sufficient to insure the formation of a uniform coating of
resin on the particulate, usually about 10 to about 30 seconds.
[0066] Following this mixing step from about 5 to about 25%, by
weight of the resin, of hexamethylenetetramine is added to the
substrate resin mixture. The preferred amount of
hexamethylenetetramine is about 13% by weight of the resin. After
addition of the hexamethylenetetramine the entire mixture is
allowed to mull for approximately one minute. Then water is added
to quench the reaction of the inner resin coating. The amount of
water added and the timing of its addition is adjusted to quench
the curing of the inner resin while maintaining sufficient heat in
the proppant to cure the outer coating that is added next.
[0067] The outer resin is then coated over the inner resin and
allowed to substantially cure. Substantially cured, as used herein,
is to be interpreted as meaning that the cross-linking reaction of
the resin is substantially complete and that at typical downhole
temperatures only minimal additional curing takes place. When the
outer coating is the preferred resole, its addition is preferably
carried out by adding it as a solution in a water/methanol mixture
comprising between 15-30% methanol and 5-15% water. The preferred
mixture is 6% water and 25% methanol.
[0068] As can be appreciated, it is useful in preparing the coated
proppant of the present embodiment of the invention to precisely
control the heat and mass balance to ensure that a cured outer
coating encapsulates a still curable inner resin coating. One
skilled in the art will recognize that batch size, equipment used,
and resins selected will affect process conditions. Initial process
temperature, process intervals, amounts of quench water added and
amounts of solvent are all interrelated and may be manipulated to
arrive at an optimal process. Although experimentation may be
required, optimization is within the level of skill in the art.
[0069] In yet another preferred embodiment, the FCC ceramic
proppant pellet is coated with a substantially cured inner resin
coating and an outer resin coating which may be heat curable, fully
cured, or of intermediate nature. A reinforcing agent may be
interspersed at the inner resin coating/outer resin coating
boundary. Suitable resins include those described above in the
previous embodiment.
[0070] A key to the increased strength of the resin coated
particles of this embodiment is the addition of a reinforcing agent
in the boundary region between the inner and outer resin coatings.
The reinforcing agents are preferably added after coating the
particle with the inner resin coating but before the inner coating
is cured.
[0071] Suitable reinforcing agents include materials known to act
as reinforcing agents in typical engineering resins and composite
materials. Common to all suitable reinforcing agents is the
requirement that they be of a particle size calculated to give the
required properties. For example, various mineral fillers including
fumed silicas, silica four, talc, clays, mica, asbestos, calcium
carbonate, calcium sulfate, metals and wollastanite are suitable.
The size of such reinforcing agents is typically less than 300
mesh. Reinforcing materials of a fibrous or rod like nature should
be less than about 0.006 inches and preferably about 0.002 inches
in length. Of these, silica flour ground to about 325 mesh is
preferred.
[0072] Another type of reinforcing agent with utility in the
present invention are impact modifiers used in engineering resins
and composite materials. Examples of such materials include
polyisobutylene, ethylene-vinyl acetate copolymers,
ethylene-propylene copolymers and other rubbery materials. Also
suitable are the so-called core shell impact modifiers having a
rubbery core with a graft polymerized crystalline shell. To obtain
the proper particle size cryogenic grinding of the rubbery
materials is useful.
[0073] In accordance with the method of the present invention, the
coated or uncoated free flowing FCC ceramic proppant pellet
particles produced as described above may be used as proppants,
gravel or fluid loss agents in hydraulic fracturing, frac packing
and gravel packs. The application will determine the choice of
whether the proppant pellet is resin coated or not, and whether the
coatings are cured or curable. For example, a curable coating may
be indicated for gravel packing, while in fracturing a
substantially cured outer coating may be preferred to prevent
interaction with the frac fluid.
[0074] In carrying out a hydraulic fracturing operation, a fracture
is first generated by injecting a viscous fluid into the formation
at a sufficient rate and pressure to cause the formation to fail in
tension. The fracturing fluid may be an oil base, water base, acid,
emulsion, foam or other fluid. The fracturing fluid may contain
several additives such as viscosity builders, drag reducers, fluid
loss additives, corrosion inhibitors, cross linkers and the like,
known in the art. Injection of the fluid is typically continued
until a fracture of the desired geometry is obtained. Preferably
the fracture at the well bore is at least 2.5 times the diameter of
the largest proppant pellet. A carrier fluid having the proppant
suspended therein is then pumped into the fracture. If the
particles are resin coated with a curable resin, the temperature of
the carrier fluid during pumping operations will be low so as to
prevent premature curing of the outer resin coat. The carrier fluid
bleeds off into the formation and deposits the proppant pellets in
the fracture. The process is controlled by fluid loss agents which
are small aggregate particles which temporarily slow the fluid loss
to the formation.
[0075] After the proppant is placed, the well is shut in with
pressure maintained on the formation. As the pressure within the
fracture approaches the normal formation pressure, the fracture
walls close in on the proppant and apply an overburden stress
thereto. Deeper wells exert higher closure stress and require
stronger proppants. Some curable resin coated proppants do not
develop their full strength until the resin coating has cured in
the formation. In the event of rapid closure of the fracture, the
proppant could be crushed before the resin cures, resulting in
decreased permeability.
[0076] When proppant pellets having an inner curable coating and an
outer substantially cured coating are used, it is believed that the
closure stress ruptures the outer coating exposing the curable
inner coating. At the same time ambient formation temperature heats
the inner resin coating. Initially, the resin fuses and unites at
contact areas between contiguous particles or with the formation
walls. As the temperature increases the polymerization reaction
proceeds until the resin is cured into an insoluble and infusible
crosslinked state. Grain to grain links are formed in pendular
regions between adjacent particles and bond the packed particles
into a permeable mass having considerable compressive strength.
[0077] It should now be apparent that various embodiments of the
present invention accomplish the object of this invention. It
should be appreciated that the present invention is not limited to
the specific embodiments described above, but includes variations,
modifications, and equivalent embodiments defined by the following
claims.
* * * * *