U.S. patent application number 10/899823 was filed with the patent office on 2005-02-10 for methods and compositions of a storable relatively lightweight proppant slurry for hydraulic fracturing and gravel packing applications.
Invention is credited to Brannon, Harold Dean, Rickards, Allan Ray, Stephenson, Christopher John, Wood, William Dale.
Application Number | 20050028979 10/899823 |
Document ID | / |
Family ID | 46302419 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050028979 |
Kind Code |
A1 |
Brannon, Harold Dean ; et
al. |
February 10, 2005 |
Methods and compositions of a storable relatively lightweight
proppant slurry for hydraulic fracturing and gravel packing
applications
Abstract
Methods and compositions useful for subterranean formation
treatments, such as hydraulic fracturing treatments and sand
control that utilize relatively lightweight and/or substantially
neutrally buoyant particulates. Particles that may be employed
include particulates of naturally occurring materials that may be
optionally strengthened or hardened by exposure to a modifying
agent; porous materials including selectively configured porous
material particles manufactured and/or treated with selected
glazing materials, coating materials and/or penetrating materials;
and well treating aggregates composed of an organic lightweight
material and a weight modifying agent. The relatively lightweight
particulate may be suspended as a substantially neutral buoyant
particulate and stored with a carrier fluid as a pumpable
slurry.
Inventors: |
Brannon, Harold Dean;
(Magnolia, TX) ; Wood, William Dale; (Spring,
TX) ; Rickards, Allan Ray; (Tomball, TX) ;
Stephenson, Christopher John; (Houston, TX) |
Correspondence
Address: |
LOCKE LIDDELL & SAPP LLP
600 TRAVIS
3400 CHASE TOWER
HOUSTON
TX
77002-3095
US
|
Family ID: |
46302419 |
Appl. No.: |
10/899823 |
Filed: |
July 27, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10899823 |
Jul 27, 2004 |
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10113844 |
Apr 1, 2002 |
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6772838 |
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10899823 |
Jul 27, 2004 |
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10653521 |
Sep 2, 2003 |
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10113844 |
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09579147 |
May 25, 2000 |
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6364018 |
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10113844 |
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09579146 |
May 25, 2000 |
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6749025 |
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09579147 |
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09519238 |
Mar 6, 2000 |
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6330916 |
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09519238 |
Mar 6, 2000 |
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09085416 |
May 27, 1998 |
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6059034 |
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09085416 |
May 27, 1998 |
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08756414 |
Nov 27, 1996 |
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09579146 |
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09519238 |
Mar 6, 2000 |
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6330916 |
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60569067 |
May 7, 2004 |
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60428836 |
Nov 25, 2002 |
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60407734 |
Sep 3, 2002 |
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Current U.S.
Class: |
166/280.2 ;
166/308.5 |
Current CPC
Class: |
C09K 8/62 20130101; C09K
8/68 20130101; C09K 8/685 20130101; C09K 8/805 20130101; C09K 8/80
20130101; E21B 43/267 20130101 |
Class at
Publication: |
166/280.2 ;
166/308.5 |
International
Class: |
E21B 043/26 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 21, 1997 |
DK |
1333/97 |
Claims
What is claimed is:
1. A storable aqueous pumpable suspension comprising: (a.) a
relatively lightweight proppant; and (b.) a carrier fluid wherein
the relatively lightweight proppant is substantially neutrally
buoyant.
2. The storable aqueous pumpable suspension of claim 1, wherein the
relatively lightweight proppant is an ultra lightweight proppant
having an apparent specific gravity less than or equal to 2.45.
3. The storable aqueous pumpable suspension of claim 2, wherein the
ULW proppant has an apparent specific gravity less than 2.35.
4. The storable aqueous pumpable suspension of claim 3, wherein the
ULW proppant has an apparent specific gravity less than 2.25.
5. The storable aqueous pumpable suspension of claim 4, wherein the
ULW proppant has an apparent specific gravity less than 2.00.
6. The storable aqueous pumpable suspension of claim 5, wherein the
ULW proppant has an apparent specific gravity less than 1.75.
7. The storable aqueous pumpable suspension of claim 6, wherein the
ULW proppant has an apparent specific gravity less than 1.25.
8. The storable aqueous pumpable suspension of claim 1, wherein the
ULW proppant is a modified naturally occurring material resistant
to deformation.
9. The storable aqueous pumpable suspension of claim 8, wherein the
ULW proppant is selected from the group consisting of ground or
crushed nut shells, ground or crushed seed shells, ground or
crushed fruit pits, processed wood, or a mixture thereof.
10. The storable aqueous pumpable suspension of claim 2, wherein
the ULW proppant is at least partially surrounded by at least one
layer of a protective or hardening coating.
11. The storable aqueous pumpable suspension of claim 2, wherein
the apparent specific gravity of the ULW proppant is preferably the
same but no greater than 0.25 higher than the apparent specific
gravity of the carrier fluid.
12. The storable aqueous pumpable suspension of claim 10, wherein
the ULW proppant is a porous particulate treated with a non-porous
penetrating, coating and/or glazing material.
13. The storable aqueous pumpable suspension of claim 12, wherein
either: (i.) the apparent specific gravity of the ULW proppant is
less than the apparent specific gravity of the porous particulate;
(ii.) the permeability of the ULW proppant is less than the
permeability of the porous particulate; or (iii.) the porosity of
the ULW proppant is less than the porosity of the porous
particulate.
14. The storable aqueous pumpable suspension of claim 12, wherein
the porous particulate comprises a multitude of coated particulates
bound together.
15. The storable aqueous pumpable suspension of claim 12, wherein
the strength of the ULW proppant is greater than the strength of
the porous particulate.
16. The storable aqueous pumpable suspension of claim 12, wherein
the porous particulate is a ceramic or organic polymeric
material.
17. The storable aqueous pumpable suspension of claim 12, wherein
the porous particulate has an internal porosity from about 10 to
about 75 volume percent.
18. The storable aqueous pumpable suspension of claim 12, wherein
the thickness of the coating of the ULW proppant is from about 1 to
about 5 microns.
19. The storable aqueous pumpable suspension of claim 12, wherein
the extent of penetration of the penetrating material is from less
than about 1% penetration by volume to less than about 25%
penetration by volume.
20. The storable aqueous pumpable suspension of claim 2, wherein
the ULW proppant is an aggregate of an organic lightweight material
and a weight modifying agent wherein the apparent specific gravity
of the organic lightweight material is either greater or less than
the apparent specific gravity of the aggregate.
21. The storable aqueous pumpable suspension of claim 20, wherein
the organic lightweight material is polymeric.
22. The storable aqueous pumpable suspension of claim 20, wherein
at least 52% by volume of the aggregate is the weight modifying
agent.
23. The storable aqueous pumpable suspension of claim 20, wherein
the amount of organic lightweight material in the aggregate is
between from about 10 to about 90 percent by volume.
24. The storable aqueous pumpable suspension of claim 20, wherein
the weight modifying agent is a weighting agent.
25. The storable aqueous pumpable suspension of claim 24, wherein
the apparent specific gravity of the aggregate is at least one and
a half times the apparent specific gravity of the organic
lightweight material.
26. The storable aqueous pumpable suspension of claim 20, wherein
the apparent specific gravity of the aggregate is at least 1.0.
27. The storable aqueous pumpable suspension of claim 25, wherein
the apparent specific gravity of the organic lightweight material
is less than or equal to 1.1.
28. The storable aqueous pumpable suspension of claim 2, wherein
the ULW proppant is an aggregate comprising, as the continuous
phase, an organic lightweight material having an apparent specific
gravity less than about 1.1 and, as the discontinuous phase, a
weighting agent, wherein the apparent specific gravity of the
aggregate is at least 1.25.
29. The storable aqueous pumpable suspension of claim 1, wherein
the carrier fluid is gelled.
30. The storable aqueous pumpable suspension of claim 1, wherein
the carrier fluid contains a suspending/thixotropic agent.
31. The storable aqueous pumpable suspension of claim 30, wherein
the suspending/thixotropic agent is selected from the group
consisting of carrageenan, scleroglucan, succinoglycan, welan gum,
xanthan gum, cellulose, guar, starch, polyalkylene oxides, and
derivatives thereof.
32. The storable aqueous pumpable suspension of claim 1, wherein
the carrier fluid further comprises at least one member selected
from the group consisting of a gelling agent, crosslinking agent,
gel breaker, surfactant, biocide, surface tension reducing agent,
foaming agent, defoaming agent, demulsifier, non-emulsifier, scale
inhibitor, gas hydrate inhibitor, polymer specific enzyme breaker,
oxidative breaker, buffer, clay stabilizer, acid or a mixture
thereof.
33. The storable aqueous pumpable suspension of claim 1, wherein
the suspension, when diluted with water, is at a concentration
suitable for fracturing a subterranean formation.
34. A storable aqueous pumpable suspension comprising at least one
ultra lightweight (ULW) proppant suspended in either (i.) a
weighted carrier fluid, wherein the apparent specific gravity of
the ULW proppant is preferably the same as, but no greater than
0.25 higher than, the apparent specific gravity of the carrier
fluid; or (ii.) a weakly gelled carrier fluid optionally containing
a friction reducing agent, wherein the amount of friction reducing
agent is between from about 0 to about 10 pounds per thousand
gallons of carrier fluid and/or the weakly gelled carrier fluid has
a viscosity of from about 1 to about 20 cps; or (iii.) a
combination of (i.) and (ii.).
35. The storable aqueous pumpable suspension of claim 34, wherein
the viscosity of the weakly gelled carrier fluid is from about 1 to
about 10 cps.
36. The storable aqueous pumpable suspension of claim 34, wherein
the ULW proppant is suspended in a weighted carrier fluid, the
apparent specific gravity of the ULW proppant being no greater than
0.20 higher than the apparent specific gravity of the carrier
fluid.
37. The storable aqueous pumpable suspension of claim 34, wherein
the carrier fluid further contains welan gum, xanthan gum,
cellulose, guar, starch or a derivative thereof.
38. The storable aqueous pumpable suspension of claim 34, wherein
the ULW proppant has a apparent specific gravity less than or equal
to 2.45.
39. The storable aqueous pumpable suspension of claim 38, wherein
the ULW proppant has an apparent specific gravity less than
2.35.
40. The storable aqueous pumpable suspension of claim 39, wherein
the ULW proppant has an apparent specific gravity less than
2.25.
41. The storable aqueous pumpable suspension of claim 40, wherein
the ULW proppant has an apparent specific gravity less than
2.00.
42. The storable aqueous pumpable suspension of claim 41, wherein
the ULW proppant has an apparent specific gravity less than
1.75.
43. The storable aqueous pumpable suspension of claim 42, wherein
the ULW proppant has an apparent specific gravity less than
1.25.
44. The storable aqueous pumpable suspension of claim 34, wherein
the ULW proppant is a modified naturally occurring material
resistant to deformation.
45. The storable aqueous pumpable suspension of claim 44, wherein
the modified naturally occurring material is selected from the
group consisting of ground or crushed nut shells, ground or crushed
seed shells, ground or crushed fruit pits, processed wood, or a
mixture thereof.
46. The storable aqueous pumpable suspension of claim 34, wherein
the ULW proppant is a porous particulate treated with a non-porous
penetrating, coating and/or glazing material.
47. The storable aqueous pumpable suspension of claim 46, wherein
either: (i.) the apparent specific gravity of the ULW proppant is
less than the apparent specific gravity of the porous particulate;
(ii.) the permeability of the ULW proppant is less than the
permeability of the porous particulate; or (iii.) the porosity of
the ULW proppant is less than the porosity of the porous
particulate.
48. The storable aqueous pumpable suspension of claim 46, wherein
the strength of the ULW proppant is greater than the strength of
the porous particulate.
49. The storable aqueous pumpable suspension of claim 46, wherein
the porous particulate is a ceramic or organic polymeric
material.
50. The storable aqueous pumpable suspension of claim 46, wherein
the porous particulate has an internal porosity from about 10 to
about 75 volume percent.
51. The storable aqueous pumpable suspension of claim 34, wherein
the ULW proppant is an aggregate of an organic lightweight material
and a weight modifying agent wherein the apparent specific gravity
of the organic lightweight material is either greater or less than
the apparent specific gravity of the aggregate.
52. The storable aqueous pumpable suspension of claim 51, wherein
the weight modifying agent is a weighting agent.
53. The storable aqueous pumpable suspension of claim 51, wherein
the apparent specific gravity of the aggregate is at least one and
a half times the apparent specific gravity of the organic
lightweight material.
54. The storable aqueous pumpable suspension of claim 51, wherein
the apparent specific gravity of the aggregate is at least 1.0.
55. The storable aqueous pumpable suspension of claim 34, wherein
wherein the carrier fluid further comprises at least one member
selected from the group consisting of a gelling agent, crosslinking
agent, gel breaker, surfactant, biocide, surface tension reducing
agent, foaming agent, defoaming agent, demulsifier, non-emulsifier,
scale inhibitor, gas hydrate inhibitor, polymer specific enzyme
breaker, oxidative breaker, buffer, clay stabilizer, acid or a
mixture thereof.
Description
[0001] The present application is a continuation-in-part
application of U.S. patent application Ser. No. 10/113,844, filed
Apr. 1, 2002 and U.S. patent application Ser. No. 10/632,521, filed
on Sep. 2, 2003. In addition, this application claims the benefit
of U.S. patent application Ser. No. 60/569,067, filed on May 7,
2004. U.S. patent application Ser. No. 10/632,521 claims benefit to
U.S. Patent Application Ser. Nos. 60/428,836, filed on Nov. 25,
2002 and 60/407,734, filed on Sep. 3, 2002. U.S. patent application
Ser. No. 10/13,844 is a continuation-in-part of U.S. patent
application Ser. No. 09/579,147, filed May 25, 2000, which issued
as U.S. Pat. No. 6,364,018, and U.S. patent application Ser. No.
09/579,146, filed May 25, 2000, both of which being a
continuation-in-part of U.S. patent application Ser. No.
09/519,238, filed Mar. 6, 2000, which issued as U.S. Pat. No.
6,330,916; which is a continuation-in-part of U.S. patent
application Ser. No. 09/085,416, filed May 27, 1998, which issued
as U.S. Pat. No. 6,059,034; which is a continuation-in-part of U.S.
patent application Ser. No. 08/756,414, filed Nov. 27, 1996, now
abandoned, and which also claims priority to Danish patent
application S/N 1333/97 filed Nov. 21, 1997; the entire disclosures
of each of the foregoing applications being incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] This invention relates generally to methods and compositions
useful for subterranean formation treatments, such as hydraulic
fracturing treatments and sand control. In particular, this
invention relates to use of relatively lightweight and/or
substantially neutrally buoyant particles as proppant material in
hydraulic fracturing treatments and as particulate material in sand
control methods such as gravel packing, frac pack treatments, etc.
In addition, this invention relates to a storable pumpable proppant
suspension containing the relatively lightweight proppant
particles.
BACKGROUND OF THE INVENTION
[0003] Hydraulic fracturing is a common stimulation technique used
to enhance production of fluids from subterranean formations. In a
typical hydraulic fracturing treatment, fracturing treatment fluid
containing a solid proppant material is injected into the wellbore
at high pressures. Once natural reservoir pressures are exceeded,
the fluid induces fractures in the formation and proppant is
deposited in the fracture, where it remains after the treatment is
completed. The proppant material serves to hold the fracture open,
thereby enhancing the ability of fluids to migrate from the
formation to the wellbore through the fracture. Because fractured
well productivity depends on the ability of a fracture to conduct
fluids from a formation to a wellbore, fracture conductivity is an
important parameter in determining the degree of success of a
hydraulic fracturing treatment.
[0004] The solid proppant materials are typically mixed with a
gelled carrier fluid (e.g., aqueous-based fluid such as gelled
brine) and injected into the well in order to create the high
conductivity channel. Gelling agents for proppant carrier fluids
may provide a source of proppant pack and/or formation damage, and
settling of proppant may interfere with proper placement downhole.
Formation damage may also be caused by gelled carrier fluids used
to place particulates downhole for purposes such as for sand
control, e.g., gravel packs, frac packs, etc.
[0005] Formulation of gelled carrier fluids usually requires
equipment and mixing steps designed for this purpose. At the time
of proppant addition, the carrier fluid exhibits poor solid
suspending properties and vigorous agitation is required to prevent
gravity segregation of the solids. A typical equipment set-up for
hydraulic fracturing is set forth in FIG. 1, wherein the carrier
fluid is delivered either from one or more pre-gelled tanks or
customized hydration units, 10A, 10B and 10C. The carrier fluid is
mixed in mixing unit 40 with buffers, breakers, surfactants and
other additives which may be required during treatment. The
proppant is delivered from one or more storage bins or silos, 20A
and 20B, by gravity and added to the fluid by way of conveyors or
augers, 30. The operation of combining the proppant with the fluid
involves the use of slurry blender 50, a relatively sophisticated
and costly piece of equipment. The slurry blender homogenizes the
mix of proppant and carrier fluid and allows the addition of
viscosifying enhancing agents, such as crosslinking agents, thus
improving proppant transport. Further, it feeds at least one high
pressure pump, shown as a series of pumps 60A, 60B and 60C, which
are used to inject the proppant slurry into the wellhead 70. The
need to "ramp" or step-up the concentration of proppant, as the
operation proceeds, requires considerable operator expertise and/or
requires the use of an array of process control equipment to enable
accurate proportioning of all the components at various rates. Any
operational failure, such as tub overflow, improper amount of
viscosity enhancer, breaker, etc., jeopardizes the operation or its
results.
[0006] Attempts have been made with conventional proppants to
obtain pumpable formulations for use on the fly. Unfortunately,
such formulations require a high degree of fluid gellation to
maintain suspension of the heavy particles. Even with heavy
gellation, such suspensions are further subject to particle
settling within a matter of hours, particularly in the presence of
vibration. This necessitates well defined mixing capabilities in
order to homogeneously re-suspend the proppants in high viscosity
suspension gels on-site. Significant costs are further incurred for
the chemicals, equipment and processing time in order to gel the
carrier fluid. Pumpable suspensions which do not exhibit particle
settling are therefore desired.
SUMMARY OF THE INVENTION
[0007] In the disclosed method, the application of relatively
lightweight and/or substantially neutrally buoyant particulate
material as a fracture proppant particulate advantageously may
provide for substantially improved overall system performance in
hydraulic fracturing applications, or in other well treating
applications such as sand control.
[0008] As used herein, the following terms shall have the
designated meanings:
[0009] "relatively lightweight" shall refer to a particulate that
has an apparent specific gravity (ASG) (API RP 60) that is
substantially less than a conventional particulate material
employed in hydraulic fracturing or sand control operations, e.g.,
sand (having an ASG, API RP 60, of 2.65) or an ASG similar to these
materials. The term "relatively lightweight" shall include ultra
lightweight (ULW) density particulates having an ASG less than or
equal to 2.45. Included within such ULW particulates are
selectively configured porous particulate materials,
non-selectively configured porous particulate materials, and well
treating aggregates, as defined herein;
[0010] "substantially neutrally buoyant" shall refer to a
relatively lightweight particulate that has an ASG sufficiently
close to the ASG of a selected ungelled or weakly gelled carrier
fluid (e.g., ungelled or weakly gelled completion brine, other
aqueous-based fluid, slick water, or other suitable fluid) which
allows pumping and satisfactory placement of the
proppant/particulate using the selected ungelled or weakly gelled
carrier fluid. For example, urethane resin-coated ground walnut
hulls having an ASG of from about 1.25 to about 1.35 may be
employed as a substantially neutrally buoyant proppant/particulate
in completion brine having an ASG of about 1.2. It will be
understood that these values are exemplary only;
[0011] "weakly gelled" carrier fluid shall refer to a carrier fluid
having minimum sufficient polymer, viscosifier or friction reducer
to achieve friction reduction when pumped downhole (e.g., when
pumped down tubing, work string, casing, coiled tubing, drill pipe,
etc.), and/or may be characterized as having a polymer or
viscosifier concentration of from greater than about 0 pounds of
polymer per thousand gallons of base fluid to about 10 pounds of
polymer per thousand gallons of base fluid, and/or as having a
viscosity of from about 1 to about 10 centipoises,
[0012] an "ungelled carrier fluid" is a carrier fluid having no
polymer or viscosifer. The ungelled carrier fluid may contain a
friction reducer known in the art;
[0013] "porous particulate material" shall refer to a porous
ceramic or porous organic polymeric material. Examples of types of
materials suitable for use as a porous particulate material include
those particulates having a porous matrix;
[0014] "selectively configured porous particulate material" shall
refer to any porous particulate material, natural or non-natural,
which has been chemically treated, such as treatment with a coating
material; treatment with a penetrating material; or modified by
glazing. The term shall include, but not be limited to, those
porous particulate materials which have been altered to achieve
desired physical properties, such as particle characteristics,
desired strength and/or ASG in order to fit downhole conditions for
well treating such as hydraulic fracturing treatments and sand
control treatments;
[0015] "non-selectively configured porous particulate material"
shall refer to any porous natural particulate material, including
porous natural ceramic materials such as lightweight volcanic
rocks, like pumice, as well as perlite and other porous "lavas"
like porous (vesicular) Hawaiian Basalt, porous Virginia Diabase,
and Utah Rhyolite. Further, inorganic ceramic materials, such as
alumina, magnetic glass, titanium oxide, zirconium oxide, and
silicon carbide may also be used. In addition, the term shall refer
to a synthetic porous particulate material which has not been
chemically treated and which imparts desired physical properties,
such as particle characteristics, desired strength and/or ASG in
order to fit downhole conditions for well treating; and
[0016] "well treating aggregate" shall refer to a relatively
lightweight particulate composed of at least one organic
lightweight material and a weight modifying agent.
[0017] The disclosed relatively lightweight and/or substantially
neutrally buoyant particulate/proppant materials may be employed
with carrier fluids that are gelled, non-gelled, or that have a
reduced or lighter gelling requirement as compared to carrier
fluids employed with conventional fracture treatment/sand control
methods. In one embodiment employing one or more of the disclosed
substantially neutrally buoyant particulate materials and a brine
carrier fluid, mixing equipment need only include such equipment
that is capable of (a) mixing the brine (dissolving soluble salts),
and (b) homogeneously dispersing in the substantially neutrally
buoyant particulate material.
[0018] Examples of suitable relatively lightweight and/or
substantially neutrally buoyant materials for use in aqueous based
carrier fluids include, but are not limited to, ground or crushed
nut shells, ground or crushed seed shells, ground or crushed fruit
pits, processed wood, or a mixture thereof as. Protective and/or
hardening coatings may be selected to modify or customize the ASG
of a selected base particulate/proppant material. Modification of
particulate specific gravity (i.e., to have a greater or lesser
specific gravity) may be advantageously employed, for example, to
provide proppant or sand control particulates of customized
specific gravity for use as a substantially neutrally buoyant
particulate with a variety of different weight or specific gravity
carrier fluids. In yet another embodiment, protective and/or
hardening-type coatings may be optionally curable to facilitate
proppant pack/sand control particulate consolidation after
placement. In this regard, curable resins are known to those of
skill in the art, and with benefit of this disclosure may be
selected to fit particular applications accordingly.
[0019] Protective coatings for coating at least a portion of
individual particles of such relatively lightweight and/or
substantially neutrally buoyant materials include, but are not
limited to at least one of phenol formaldehyde resin, melamine
formaldehyde resin, urethane resin, or a mixture thereof. Other
optional coating compositions known in the art to be useful as
hardeners for such materials (e.g., coating materials that function
or serve to increase the elastic modulus of the material) may be
also employed in conjunction or as an alternative to protective
coatings, and may be placed underneath or on top of one or more
protective coatings. It will be understood by those of skill in the
art that such protective and/or hardening coatings may be used in
any combination suitable for imparting desired characteristics to a
relatively lightweight and/or substantially neutrally buoyant
particulate/proppant material, including in two or more multiple
layers. In this regard successive layers of protective coatings,
successive layers of hardening coatings, alternating layers of
hardening and protective coatings, etc. are possible. Mixtures of
protective and hardening coating materials may also be
possible.
[0020] Suitable relatively lightweight and/or substantially
neutrally buoyant particulate materials coated with a resin may
have a specific gravity of from about 1.25 to about 1.35, and a
bulk density of about 0.67. In one exemplary case, size of such a
material may be about 12/20 US mesh size. In another exemplary
case, sizes may range from about 4 mesh to about 100 mesh.
Advantageously, in some embodiments, ground walnut shells may serve
to attract fines and formation particles by their resinous
nature.
[0021] In one particularly preferred embodiment, an optional
hardener may be applied to a ground walnut shell material first
followed by a urethane coating as described elsewhere herein that
may vary in amount as desired. For example, such a coating material
may be present in an amount of from about 1% to about 20%,
alternatively from about 10% to about 20% by weight of total weight
of individual particles. Alternatively, such a coating material may
be present in an amount of from about 2% to about 12% by weight of
total weight of individual particles. The amount of resin may
depend, for example, on price and application. In this regard,
particulates may be first sprayed or otherwise coated with a
hardener, and a coating may be applied to be about 12% by weight of
total weight of the particle.
[0022] In a further embodiment, individual particles (e.g.,
granules) of naturally occurring materials (e.g., made from
naturally occurring materials or derivatives of naturally occurring
materials including, but not limited to, plant-based or
agricultural-based materials such as nut hulls, seed shells,
processed wood materials, derivatives of such plant-based or
agricultural-based materials, etc.) may be optionally treated by
exposure to a modifying agent that is capable of interacting with
compounds present in or on a natural material in a way that acts to
increase the ability of the naturally occurring material to resist
deformation (e.g., by increasing the elastic modulus or otherwise
strengthening and/or hardening the naturally occurring material).
Examples of suitable modifying agents include, but are not limited
to, any compound or other material capable of modifying (e.g.,
crosslinking, coupling or otherwise reacting with) one or more
components present in the naturally occurring material (e.g.,
natural resins, lignins and/or cellulosic fibers). Specific
examples of suitable modifying agents include, but are not limited
to, agents including polyisocyanates, silanes, siloxanes, and
combinations thereof. Selected modifying agent/s may be
advantageously used to increase the elastic modulus of a given
naturally occurring material, for example, to make particles of a
given naturally occurring material more suitable (e.g., having
increased hardness or strength to resist or prevent deformation
under downhole in situ conditions of formation temperature and
formation closure stress) for use as a relatively lightweight
and/or substantially neutrally buoyant fracture proppant or sand
control particulate material having increased effectiveness when
exposed to higher closure stresses or other mechanical stresses
that may be encountered downhole during a well treatment such as a
hydraulic fracturing or sand control treatment.
[0023] Effectiveness of modifying agents may be optionally
enhanced, for example, by facilitating interaction between a
modifying agent and one or more components present in a naturally
occurring material. In this regard interaction between a modifying
agent and components present in a naturally occurring material may
be facilitated using one or more enhancing agents (e.g., swelling
agents, penetrating agents, etc.) and/or by exposing a naturally
occurring material to one or more interaction-enhancing conditions
that serve to enhance interaction with a modifying agent (e.g.,
vacuum and/or pressure impregnation of the modifying agent into a
naturally occurring material, etc.). Examples of suitable enhancing
agents include, but are not limited to, liquid or gaseous ammonia,
dimethyl sulfoxide ("DMSO"), methyl pyrrolidone, etc.
[0024] In one exemplary embodiment, the modifying process may
include exposing particles of the naturally occurring material to a
modifying agent (e.g., that includes an aqueous mixture of alkyl
silanes, such as aminopropyltriethoxy silane) to strengthen the
naturally occurring material against deformation under closure
stress. The modifying agent may be exposed to the naturally
occurring materials using any suitable method, including soaking or
spraying, and may be allowed to interact or react with the
naturally occurring material with or without heating. The particles
of naturally occurring material may also be optionally exposed to
an enhancing agent (e.g., liquid ammonia) to allow deeper
penetration and interaction of the modifying agent with components
of the naturally occurring material, thus providing more uniform
crosslinking or coupling of these components with less modifying
agent and also helping to minimize or avoid localized crosslinking
or coupling within the particles. A coating or layer of a material
such as resin or epoxy may be added after treatment with a
modifying agent to further enhance or increase strength of the
naturally occurring material, and/or to minimize downhole fluid
incompatibilities.
[0025] Also disclosed herein is a method of using modified
particles of naturally occurring material as a relatively
lightweight particulate material that may be introduced as part of
a treating fluid into a well down wellbore tubulars (e.g., tubing,
workstring, casing, drillpipe) or down coiled tubing, for example
at concentrations of about 0.25 to about 15 pounds per gallon of
treating fluid. In one exemplary embodiment, specific gravity of
the particles of modified naturally occurring material may be about
1.3, and therefore they may be used as a substantially neutrally
buoyant proppant or sand control particulate in light or heavy
brines, thus eliminating the need for complex crosslinked
fracturing or sand control carrier fluids.
[0026] The relatively lightweight and/or substantially neutrally
buoyant particle may further be a porous ceramic or organic
polymeric particulates and, in particular, selectively configured
porous particulate material or a non-selectively configured porous
particulate material, as defined herein.
[0027] The porous particulate material may be selectively
configured with a non-porous penetrating material, coating layer or
glazing layer. In a preferred embodiment, the porous particulate
material is a selectively configured porous particulate material
wherein (a) the ASG of the selectively configured porous
particulate material is less than the ASG of the porous particulate
material; (b) the permeability of the selectively configured porous
particulate material is less than the permeability of the porous
particulate material; or (c) the porosity of the selectively
configured porous particulate material is less than the porosity of
the porous particulate material.
[0028] In a preferred embodiment, the penetrating material and/or
coating layer and/or glazing layer of the selectively configured
porous particulate material is capable of trapping or encapsulating
a fluid having an ASG less than the ASG of the carrier fluid.
Further, the coating layer and/or penetrating material and/or
glazing material may be a liquid having an ASG less than the ASG of
the matrix of the porous particulate material.
[0029] The strength of the selectively configured porous
particulate material is typically greater than the strength of the
porous particulate material per se.
[0030] In a preferred mode, the porous particulate composition is a
suspension of porous particulates in a carrier fluid. The
suspension preferably forms a pack of particulate material that is
permeable to fluids produced from the wellbore and substantially
prevents or reduces production of formation materials from the
formation into the wellbore.
[0031] Further, the porous particulate material may exhibit a
porosity and permeability such that a fluid may be drawn at least
partially into the porous matrix by capillary action. Preferably,
the porous particulate material has a porosity and permeability
such that a penetrating material may be drawn at least partially
into the porous matrix of the porous particulate material using a
vacuum and/or may be forced at least partially into the porous
matrix under pressure.
[0032] The selectively configured porous particulate material may
consist of a multitude of coated particulates bonded together. In
such manner, the porous material is a cluster of particulates
coated with a coating or penetrating layer or glazing layer.
Suitable coating layers or penetrating materials include liquid
and/or curable resins, plastics, cements, sealants, or binders such
as a phenol, phenol formaldehyde, melamine formaldehyde, urethane,
epoxy resin, nylon, polyethylene, polystyrene or a combination
thereof. In a preferred mode, the coating layer or penetrating
material is an ethyl carbamate-based resin.
[0033] Further, the relatively lightweight and/or substantially
neutrally buoyant particles may be a well treating aggregate
composed of an organic lightweight material and a weight modifying
agent. The ASG of the organic lightweight material is either
greater than or less than the ASG of the well treating aggregate
depending on if the weight modifying agent is a weighting agent or
weight reducing agent, respectively.
[0034] Where the weight modifying agent is a weighting agent, the
ASG of the well treating aggregate is at least one and a half times
the ASG of the organic lightweight material, the ASG of the well
treating aggregate preferably being at least about 1.0, preferably
at least about 1.25. In a preferred embodiment, the ASG of the
organic lightweight material in such systems is approximately 0.7
and the ASG of the well treating aggregate is between from about
1.05 to about 1.20.
[0035] Where the weight modifying agent is a weight reducing agent,
the ASG of the weight reducing agent is less than 1.0 and the ASG
of the organic lightweight material is less than or equal to
1.1.
[0036] In a preferred mode, the organic lightweight material forms
the continuous (external) phase for the well treating aggregate,
whereas the weight modifying agent forms the discontinuous
(internal) phase.
[0037] The weight modifying agent may be sand, glass, hematite,
silica, sand, fly ash, aluminosilicate, and an alkali metal salt or
trimanganese tetraoxide. Further, the weight modifying agent may be
a cation selected from alkali metal, alkaline earth metal,
ammonium, manganese, and zinc and an anion selected from a halide,
oxide, a carbonate, nitrate, sulfate, acetate and formate. Glass
bubbles and fly ash are preferred when the weight modifying agent
is a weight reducing agent. The organic lightweight material is
preferably a thermosetting resin.
[0038] The relatively lightweight particulates of the invention
exhibit crush resistance under conditions as high as 10,000 psi
closure stress, API RP 56 or API RP 60.
[0039] In one embodiment, the disclosed relatively lightweight
particulate may be introduced or pumped into a well as neutrally
buoyant particles in, for example, a saturated sodium chloride
solution carrier fluid or a carrier fluid that is any other
completion or workover brine known in the art, for example, having
an ASG of from about 1 to about 1.5, alternatively from about 1.2
to about 1.5, further alternatively about 1.2, thus eliminating the
need for damaging polymer or fluid loss material. In one
embodiment, such a material may be employed as proppant/sand
control particulate material at temperatures up to about
150.degree. F., and pressures up to about 1500 psi. However, these
ranges of temperature and closure stress are exemplary only, it
being understood that the disclosed materials may be employed as
proppant/sand control materials at temperatures greater than about
1 50.degree. F. and/or at closure stresses greater than about 1500
psi. For example, particles of naturally occurring material may be
exposed to suitable modifying agents, with or without enhancing
agents and/or conditions, in one embodiment to form relatively
lightweight particulate materials that may be employed as proppant
or sand control particulate at temperatures up to about 300.degree.
F., and/or at closure stresses up to about 10,000 psi, with
temperatures greater than about 300.degree. F. and/or closure
stresses greater than about 10,000 psi also being possible. In any
event, it will be understood with benefit of this disclosure that
core and/or layer material/s (when present) and/or
interaction-enhancing materials/conditions may be selected by those
of skill in the art to meet and withstand anticipated downhole
conditions of a given application.
[0040] In still another respect, the relatively lightweight
particulate may be advantageously pre-suspended as a substantially
neutrally buoyant particulate and stored in the carrier fluid
(e.g., brine of near or substantially equal density), and then
pumped or placed downhole as is, or diluted on the fly. In a
preferred embodiment, the particulate is an ultra lightweight (ULW)
proppant and is suspended in either a weighted carrier fluid or a
weakly gelled carrier fluid. When suspended in the weighted carrier
fluid, the ASG of the ULW proppant in the weighted carrier fluid is
the same as, but no greater than 0.25 higher than, the ASG of the
carrier fluid.
[0041] The carrier fluid may be a completion or workover brine,
salt water, fresh water, a liquid hydrocarbon, or a gas such as
nitrogen or carbon dioxide.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] In order to more fully understand the drawings referred to
in the detailed description of the present invention, a brief
description of each drawing is presented, in which:
[0043] FIG. 1 shows an exemplary hydraulic fracturing equipment
set-up used in the prior art.
[0044] FIG. 2 is a representation of a particle of ground walnut
hull material according to one embodiment of the disclosed
method.
[0045] FIG. 3 exemplifies the base equipment for a hydraulic
fracturing treatment using a pre-slurried relatively lightweight
proppant stored in accordance with the invention.
[0046] FIG. 4 exemplifies alternative base equipment with water
storage for dilution for use in a hydraulic fracturing treatment
using a pre-slurried relatively lightweight proppant stored in
accordance with the invention.
[0047] FIG. 5 shows permeability versus closure stress for
particulate according to one embodiment of the disclosed
method.
[0048] FIG. 6 shows cell width versus closure stress for
particulate according to one embodiment of the disclosed
method.
[0049] FIG. 7 shows permeability versus closure stress for
particulate according to one embodiment of the disclosed
method.
[0050] FIG. 8 shows pack width displacement versus closure stress
for particulate according to one embodiment of the disclosed
method.
[0051] FIG. 9 is a graph depicting bulk apparent density comparison
of the data of Example 6.
[0052] FIG. 10 is a graph depicting permeability versus closure
stress data of Example 6.
[0053] FIG. 11 is a graph depicting conductivity versus closure
stress data of Example 6.
[0054] FIG. 12 is a graph depicting conductivity versus closure
stress data of Example 7.
[0055] FIG. 13 is a graph depicting permeability versus closure
stress data of Example 7.
[0056] FIG. 14 is a graph depicting conductivity comparison data of
Example 7.
[0057] FIG. 15 is a graph depicting permeability comparison data of
Example 7.
[0058] FIG. 16 is a SEM photograph of a porous material particle of
Example 8.
[0059] FIG. 17 is a SEM photograph of a porous material particle of
Example 8.
[0060] FIG. 18 is a SEM photograph of a porous material particle of
Example 8.
[0061] FIG. 19 is a SEM photograph of a porous material particle of
Example 8.
[0062] FIG. 20 is a SEM photograph of a porous material particle of
Example 8.
[0063] FIG. 21 is a SEM photograph of a porous material particle of
Example 8.
[0064] FIG. 22 a SEM photograph of a porous material particle of
Example 8.
[0065] FIG. 23 is a SEM photograph of a porous material particle of
Example 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0066] The invention employs relatively lightweight and/or
substantially neutrally buoyant proppant or sand control
particulates for treating a well penetrating subterranean
formation.
[0067] In a preferred embodiment of the invention, the
proppant/particulate is an ultra lightweight (ULW)
proppant/particulate having an apparent specific gravity (ASG) less
than or equal to 2.45. Generally, the ASG of the ULW proppant is
less than or equal to 2.25, more preferably less than or equal to
2.0, even more preferably less than or equal to 1.75, most
preferably less than or equal to 1.25.
[0068] The relatively lightweight particulate is preferably
selected from a modified naturally occurring material resistant to
deformation, a porous particulate treated with a non-porous
penetrating coating and/or glazing material or is a well treating
aggregate of an organic lightweight material and a weight modifying
agent or is a mixture thereof.
[0069] Such relatively lightweight particulate materials may be
easier to place within a targeted zone due to lessened settling
constraints. The reduced mass of such relatively lightweight
particulate materials is generally required to fill an equivalent
volume than is required with conventional sand control particulates
used, for example, for gravel packing purposes.
[0070] Elimination of the need to formulate a complex suspension
gel may mean a reduction in tubing friction pressures, particularly
in coiled tubing and in the amount of on-location mixing equipment
and/or mixing time requirements, as well as reduced costs.
Furthermore, when treated to have sufficient strength (e.g., by
substantially filling the permeable porosity of a porous particle
with resin or hardener), the disclosed relatively lightweight
particulates may be employed to simplify hydraulic fracturing
treatments or sand control treatments performed through coil
tubing, by greatly reducing fluid suspension property requirements.
Downhole, a much reduced propensity to settle (as compared to
conventional proppant or sand control particulates) may be
achieved, particularly in highly deviated or horizontal wellbore
sections. In this regard, the disclosed substantially neutral
buoyancy particulates may be advantageously employed in any
deviated well having an angle of deviation of between about
0.degree. and about 90.degree. with respect to the vertical.
However, in one embodiment, the disclosed particulate material may
be advantageously employed in horizontal wells, or in deviated
wells having an angle with respect to the vertical of between about
30.degree. and about 90.degree., alternatively between about
75.degree. and about 90.degree..
[0071] The relatively lightweight particulate exhibits crush
resistance under conditions as high as 10,000 psi closure stress,
API RP 56 or API RP 60, generally between from about 250 to about
8,000 psi closure stress.
[0072] The low ASG of the relatively lightweight and/or
substantially neutrally buoyant particulate may result in a larger
fracture or frac pack width for the same loading (i.e., pound per
square foot of proppant) to give much larger total volume and
increased width for the same mass. Alternatively, this
characteristic allows for smaller masses of proppant or sand
control particulates to be pumped while still achieving an
equivalent width.
[0073] Such materials may be employed in a manner that eliminates
the need for gellation of carrier fluid, thus eliminating a source
of potential proppant pack and/or formation damage and enhancement
of well productivity.
[0074] Alternatively, in one embodiment, the relatively lightweight
particulate may be introduced or pumped into a well as neutrally
buoyant particles in the carrier fluid, eliminating the need for
damaging polymer or fluid loss material. In one embodiment, such a
material may be employed as proppant/sand control particulate
material at temperatures up to about 700.degree. F., and closure
stresses up to about 8000 psi. However, these ranges of temperature
and closure stress are exemplary only, it being understood that the
disclosed materials may be employed as proppant/sand control
materials at temperatures greater than about 700.degree. F. and/or
at closure stresses greater than about 8000 psi.
[0075] The disclosed particulates may be mixed with a carrier fluid
in any manner suitable for delivering the mixture to a wellbore
and/or subterranean formation. In one embodiment, the disclosed
particulates may be injected into a subterranean formation in
conjunction with a hydraulic fracturing treatment or other
treatment at pressures sufficiently high enough to cause the
formation or enlargement of fractures, or to otherwise expose the
particles to formation closure stress. Such other treatments may be
near wellbore in nature (affecting near wellbore regions) and may
be directed toward improving wellbore productivity and/or
controlling the production of fracture proppant or formation sand.
Particular examples include gravel packing and "frac-packs."
Moreover, such particulates may be employed alone as a fracture
proppant/sand control particulate, or in mixtures in amounts and
with types of fracture proppant/sand control materials, e.g.
conventional fracture or sand control particulate. Further
information on hydraulic fracturing methods and materials for use
therein may be found in U.S. Pat. No. 6,059,034 and in U.S. Pat.
No. 6,330,916, which are incorporated herein by reference.
[0076] The particulates are mixed at their desired concentration
with a carrier fluid. The ASG of the particulate is less than or
equal to the ASG of the carrier fluid. Any carrier fluid suitable
for transporting the particulate into a well and/or subterranean
formation fracture in communication therewith may be employed
including, but not limited to, carrier fluids including a
completion or workover brine, salt water, fresh water, potassium
chloride solution, a saturated sodium chloride solution, liquid
hydrocarbons, and/or nitrogen, carbon dioxide or other gases.
[0077] Modified Naturally Occurring Materials
[0078] Suitable relatively lightweight and/or substantially
neutrally buoyant proppant or sand control particulates include
naturally occurring materials. Such naturally occurring materials
may be strengthened or hardened by use of modifying agents to
increase the ability of the naturally occurring material to resist
deformation.
[0079] Examples of such naturally occurring materials include, but
are not limited to, any naturally occurring material that contains
naturally occurring and crosslinkable molecules or compounds (e.g.,
mixtures of naturally occurring resins, lignins and/or polymers
that may be crosslinked). In this regard, examples of naturally
occurring and cross-linkable molecules or compounds include, but
are not limited to, those molecules having available hydroxyl
groups suitable for crosslinking with one or more crosslinking
agent/s. Specific examples of such molecules include, but are not
limited to, polysaccharides found in plants that serve to enhance
strength of plant materials including, but not limited to,
polysaccharides containing Beta (1-4) linked sugars. Specific
examples include, but are not limited to, cellulose and mannans.
Other examples of suitable molecules or components include, but are
not limited to, natural resins and ligands, specific substances
such as polyphenolic esters of glucosides found in tannin from
walnut hulls, etc. It will be understood that the term "naturally
occurring material" is used herein to describe any material based
on a naturally occurring substance having the characteristics as
described further herein. Materials based on naturally occurring
materials include, but are not limited to, both underived and/or
unprocessed naturally occurring materials, as well as materials
based on naturally occurring materials that have been processed
(e.g., mechanically or chemically processed) and/or derived (e.g.,
derivatives of naturally occurring materials).
[0080] Specific examples of naturally occurring particulate
materials suitable for treatment with modifying agent/s and/or
suitable for use as relatively lightweight and/or substantially
neutrally buoyant proppant or sand control particulates include,
but are not limited to, ground or crushed shells of nuts such as
walnut, coconut, pecan, almond, ivory nut, brazil nut, etc.; ground
or crushed seed shells (including fruit pits) of seeds of fruits
such as plum, olive, peach, cherry, apricot, etc.; ground or
crushed seed shells of other plants such as maize (e.g., corn cobs
or corn kernels), etc.; processed wood materials such as those
derived from woods such as oak, hickory, walnut, poplar, mahogany,
etc., including such woods that have been processed by grinding,
chipping, or other form of particalization, processing, etc.
Further information on nuts and composition thereof may be found in
Encyclopedia of Chemical Technology, edited by Raymond E. Kirk and
Donald F. Othmer, Third Edition, John Wiley & Sons, Volume 16,
pages 248-273 (entitled "Nuts"), copyright 1981, which is
incorporated herein by reference.
[0081] Additional information on materials and methods for use
thereof may be found in U.S Pat. No. 6,330,916. Further information
on materials and methods may also be found in U.S. patent
application Ser. No. 09/579,147, filed May 25, 2000, and U.S.
patent application Ser. No. 09/579,146, filed May 25, 2000, each of
which is incorporated herein by reference.
[0082] Specific examples of suitable materials for use in both
relatively low closure stress embodiments and in relatively higher
closure stress embodiments (e.g., when treated with a modifying
agent as described herein) include, but are not limited to, ground
or crushed nut shells available from suppliers such as "COMPOSITION
MATERIALS, INC." of Milford, Conn.; "AGRASHELL, INC." of Bath, Pa.;
"BAROID", and/or "CALIFORNIA NUT ASSOCIATION"; "WALNUT SHELLING,
INC." of Las Molinas, Calif.; and "ECOSHELL" of Corning, Calif.
These products include "walnut shell grit" available from
"COMPOSITION MATERIALS, INC.", "AD-3" ground walnut hulls from
"AGRASHELL" (having a particle size of about 12/20 mesh, an ASG of
about 1.2, and a maximum length-based aspect ratio of about 5), as
well as "AD-6B" ground walnut shells (having a particle size of
about 20/40 mesh, an ASG of about 1.2, and a maximum length-based
aspect ratio of about 5). Such ground walnut hull material is
available, e.g., for use as a blasting media. Other suitable
products include, but are not limited to, ground walnut hull
material from "ECOSHELL" or "FRITZ" having a particle size of about
16/30 mesh, an ASG of about 1.3, and a maximum length-based aspect
ratio of about 1:1, alternatively of about 2:1.
[0083] FIG. 2 shows a simplified representation of a particle 600
of ground walnut hull material having relative dimension ratio of
X:Y:Z. In one exemplary embodiment employing ground walnut hull
material, values of X, Y and Z may be expressed as a relative ratio
(e.g., independent of any particular units of measurement employed)
as follows: X may be from about 1 to about 5; Y may be from about 1
to about 5, and Z may be about 1. Alternatively, X may be from
about 2 to about 5; Y may be from about 2 to about 5, and Z may be
about 1. These given ranges are exemplary only, and relative
dimensional values of any one or more of X, Y, and Z may fall
outside these value ranges. In alternate embodiments, ground nuts
such as ground walnut hulls may be processed to have a
substantially spherical or beaded shape as well.
[0084] In one exemplary embodiment, ground walnut hulls having a
particle size of about 12/20 mesh and a maximum length-based aspect
ratio of about 5 may be employed as a proppant and/or sand control
particulate. These and other materials may be treated (e.g., with
modifying agent and/or coated) for use in these applications as
described elsewhere herein.
[0085] As previously mentioned, naturally occurring materials may
be optionally strengthened or hardened in one embodiment by
exposure to a modifying agent that is capable of interacting with
compounds present in or on a naturally occurring material in a way
that acts to strengthen or harden the naturally occurring material
(e.g., by increasing the elastic modulus of the naturally occurring
material). In this regard, any naturally occurring material and/or
derivatized naturally occurring material may be employed that is
suitable for treatment with one or more modifying agent/s in a
manner as described elsewhere herein. A suitable naturally
occurring material may include, for example, any material or
derivatized material that contains naturally occurring and
crosslinkable molecules or compounds (e.g., mixtures of naturally
occurring resins, lignins and/or polymers that may be crosslinked).
Examples of naturally occurring and cross-linkable molecules or
compounds include, but are not limited to, those molecules having
terminal hydroxyl groups suitable for crosslinking with one or more
crosslinking agent/s. Specific examples of such molecules include,
but are not limited to, polysaccharides composed of .beta.(1-4)
linked sugars such as cellulose, mannose, etc. In one exemplary
embodiment, individual particles (e.g., granules) of naturally
occurring materials (e.g., made from nut hulls, seed shells,
processed wood materials, etc.) may be employed. Included are any
of the specific examples of nut hulls, seed shells and processed
wood materials described elsewhere herein.
[0086] Selected modifying agent/s may be advantageously used to
modify particles of a given naturally occurring material so that
they have increased resistance (e.g., partial or complete
resistance) to deformation under in situ formation or downhole
conditions as compared to the same type of particles of naturally
occurring material that have not been so modified. In this regard,
a selected modifying agent/s may be employed to make particles of a
given naturally occurring material more suitable for use as a
fracture proppant and/or sand control particulate material having
increased effectiveness when exposed to higher closure stresses or
other mechanical stresses that may be encountered downhole during a
well treatment such as a hydraulic fracturing or sand control
treatment. In one exemplary embodiment, a modifying agent/s may be
characterized as an agent that is effective to increase the
hardness or strength of a given naturally occurring material (e.g.,
one that is effective to increase the elastic modulus of the given
naturally occurring material). While not wishing to be bound by
theory, it is believed that a modifying agent may increase the
resistance to deformation of a given naturally occurring material
by reacting (e.g., crosslinking) with components (e.g., resins,
polymers, etc.) present in the naturally occurring material.
[0087] In one embodiment, one or more modifying agents may be
employed to significantly increase the elastic modulus of a given
naturally occurring material as measured under standard conditions
of temperature and pressure ("STP"). For example, in one exemplary
embodiment, particles of ground walnut hulls having an untreated
elastic modulus of about 40,000 psi to about 50,000 psi may be
treated with one or more of the modifying agents described herein
to increase the elastic modulus to a value greater than or equal to
about 40,000 psi, alternatively to a value greater than or equal to
about 50,000 psi, alternatively to a value from about 40,000 psi to
about 1,500,000 psi, alternatively to a value from about 40,000 psi
to about 1,000,000 psi, alternatively to a value from about 40,000
psi to about 500,000 psi, alternatively to a value from about
40,000 psi to about 400,000 psi, alternatively to a value from
about 50,000 psi to about 1,500,000 psi, alternatively to a value
from about 50,000 psi to about 1,000,000 psi, alternatively to a
value from about 50,000 psi to about 500,000 psi, alternatively to
a value from about 50,000 psi to about 400,000 psi, alternatively
to a value of from about of from about 400,000 psi to about
1,500,000 psi, alternatively to a value of from about 500,000 psi
to about 1,000,000 psi, alternatively to a value of greater than or
equal to about 400,000 psi, alternatively to a value of greater
than or equal to about 500,000 psi, alternatively to a value of
greater than or equal to about 1,000,000 psi, alternatively to a
value of from about 1,000,000 psi to about 1,500,000 psi, with it
being understood that these values are exemplary only and that
values outside these ranges are also possible. In other
embodiments, it is possible that treatment with one or more
modifying agents may also serve to at least partially increase the
ability of naturally occurring particulate material to withstand
damage or degradation from exposure to downhole fluids such as
formation, drilling, workover fluids (e.g., salt water, acid,
etc.), although it will be understood that this characteristic need
not necessarily be present.
[0088] In one embodiment, examples of suitable modifying agents
include, but are not limited to, any compound or other material
effective for modifying (e.g., crosslinking, coupling or otherwise
reacting with) one or more components present in the naturally
occurring material (e.g., natural resins, lignins and/or cellulosic
fibers). In a further embodiment, suitable modifying agents may be
optionally further characterized as being effective for modifying
one or more components present in a occurring-occurring material
without degrading or otherwise damaging strength or hardness of
naturally occurring material (e.g., without causing hydrolysis of
the resins and polysaccharides), and/or without producing damaging
by-products during modification that act to degrade or otherwise
damage strength or hardness of naturally occurring material (e.g.,
without liberating acids such as hydrochloric acid, organic acids,
etc.). In one exemplary embodiment, modification by-products
produced by a suitable modifying agent may be characterized as
substantially non-reactive and non-damaging to the strength or
hardness of a given modified occurring-occurring particulate
material (e.g., alcohol-based by-product such as methanol being
substantially non-damaging to ground walnut hull material). It is
also possible that such substantially non-damaging by-products may
be optionally released or liberated from the naturally occurring
material during post-modification treatment, e.g., drying of a
modified occurring-occurring particulate material.
[0089] Examples of suitable types of modifying agents include, but
are not limited to, compounds containing silicon-oxygen linkages,
compounds containing cyanate groups, epoxy groups, etc. Specific
examples of suitable modifying agents include, but are not limited
to, polyisocyanate-based compounds, silane-based compounds,
siloxane-based compounds, epoxy-based combinations thereof,
etc.
[0090] In one embodiment, a modifying agent may include one or more
silane-based compounds having the following chemical formula
(I):
R--Si(OR').sub.3 (I)
[0091] wherein in one embodiment R is branched or linear aliphatic
carbon chain that may be saturated or unsaturated (e.g., containing
one or more double and/or triple bonds), and which may have from
about 1 to about 10 carbon atoms, alternatively from about 1 to
about 5 carbon atoms, and further alternatively about 3 carbon
atoms; and wherein each R' is independently branched or linear
carbon chain that may be saturated or unsaturated (e.g., containing
one or more double and/or triple bonds), and which may have from
about 1 to about 4 carbon atoms, alternatively from about 1 to
about 2 carbon atoms, and further alternatively about 2 carbon
atoms; it being understood that each R' group may be the same or
different structure than one or both of the other R' groups. In
another embodiment, R may be further characterized as alkanyl or
alkenyl carbon chain having the above-properties. In other
embodiments, R may be characterized as an aromatic carbon chain or
alicyclic carbon chain.
[0092] In a further embodiment, one or more of the carbon chains R
and/or R' of formula (I) may be optionally and independently
derivatized, e.g., the R carbon chain and/or one or more of the R'
carbon chains may each contain one or more amino functional groups,
one or more halogen groups (e.g., tetrachlorosilane,
methyltrichlorosilane, etc.), two or more isocyanate functional
groups, two or more epoxy groups, etc. Where halogen groups (e.g.,
such as chlorine groups) are present, it may be desirable to
rapidly neutralize any acidic by-products that may be created
during a modification reaction.
[0093] In one exemplary embodiment, a silane-based modifying agent
may include an amino-functional silane-based compound such as
gamma-aminopropyltriethoxy silane, a isocyanate-functional
silane-based compound such as gamma isocyanatopropyltriethoxy
silane, mixtures thereof, etc.
[0094] Examples of commercially available silane-based products
that may be employed as modifying agents in the practice of the
disclose methods and compositions include, but are not limited to,
silane-based products (e.g., as crosslinkers, coupling agents,
adhesion promoters, stereomodifiers, endcappers, etc.) available
from sources such as NALCO/EXXON CHEMICALS and CROMPTON of South
Charleston, W.Va. Specific examples of commercially available
silane-based products available from CROMPTON include CoatOSil.RTM.
1706 Silane (vinyl silane monomer), CoatOSil.RTM. 1757 Silane,
CoatOSil.RTM. 1770 Silane, EURENOR.RTM. 5020 (liquid
isobuytlisopropyldimethoxysilane), EURENOR.RTM. 5021 (liquid
diisopropylmethoxysilane), EURENOR.RTM. 5022 (liquid
diisobutyldimethoxysilane), EURENOR.RTM. 5023 (liquid
dicyclopentyldimethoxysilane), Silcat.RTM. R Silane (vinylsilane
with grafting and crosslinking catalysts), Silcat.RTM. RHE Silane
(crosslinking system of silane, peroxide and catalyst), Silcat.RTM.
RHS Silane (crosslinking system of silane, peroxide catalyst and
antioxidants), Silcat.RTM. VS-735/1 Silane (crosslinking system of
silane, peroxide, antioxidants and metal deactivator), Silcat.RTM.
VS-758/0 Silane (stabilized crosslinking system of silane, peroxide
and catalyst), Silcat.RTM. VS-870 Silane (stabilized crosslinking
system of silane, peroxide, catalyst, antioxidants and metal
deactivator), Silcat.RTM. VS-928 Silane (stabilized crosslinking
system of silane, peroxide, catalyst, antioxidants and metal
deactivator), Silcat.RTM. VS-963 Silane (stabilized crosslinking
system of silane, peroxide, catalyst, antioxidants and metal
deactivator), Silox.RTM. VS-911 Silane (liquid silane system),
Silquest.RTM. A-1100.TM. Silane (gamma-aminopropyltriethoxysilane),
Silquest.RTM. A-1101 Silane (technical grade amino silane),
Silquest.RTM. A-1102 Silane (technical grade amino silane),
Silquest.RTM. A-1110 Silane (primary amino silane), Silquest.RTM.
A-1120 Silane, Silquest.RTM. A-1126 Silane (amino silane),
Silquest.RTM. A-1128 Silane (amino silane), Silquest.RTM. A-1160
Silane (ureido silane), Silquest.RTM. A-1170 Silane (secondary
aminofunctional silane), Silquest.RTM. A-1289 Silane, Silquest.RTM.
A-1310 Silane, Silquest.RTM. A-137 Silane (monomeric
alkylalkoxysilane), Silquest.RTM. A-151 Silane, Silquest.RTM.
A-1524 Silane (100-percent active ureidosilane), Silquest.RTM.
A-1589 Silane (disulfide silane), Silquest.RTM. A-171 Silane,
Silquest.RTM. A-172 Silane (vinylfunctional coupling agent),
Silquest.RTM. A-174 Silane, Silquest.RTM. A-186 Silane (epoxy
functional silanes), Silquest.RTM. A-187 Silane (epoxy functional
silanes), Silquest.RTM. A-189 Silane, Silquest.RTM. A-2171 Silane
(silane compound having vinyl and silane functionality),
Silquest.RTM. Alink 15 Silane (secondary amino silane endcapper),
Silquest.RTM. RC-1 Silane (organosilicone coupling agent),
Silquest.RTM. RC-2 Silane, Silquest.RTM. Wetlink 78 Silane,
Silquest.RTM. Y-11637 Silane (primary aminosilane), Silquest.RTM.
Y-11683 Silane (di-, tri-functional ethoxy silane), Silquest.RTM.
Y-5997 Silane, XL-PEarl.RTM. 31 Blend, XL-PEarl.RTM. 50 Blend,
XL-PEarl.RTM. 51 Blend, XL-PEarl.RTM. 52 Blend, XL-PEarl.RTM. 60
Blend, XL-PEarl.RTM. 70 Blend, etc.
[0095] In another embodiment, a modifying agent may include one or
more siloxane-based compounds having the following chemical formula
(II):
R--Si(OR').sub.2--O--Si(OR").sub.2--R (II)
[0096] wherein in one embodiment R is a branched or linear
aliphatic carbon chain that may be saturated or unsaturated (e.g.,
containing one or more double and/or triple bonds), and which may
have from about 1 to about 10 carbon atoms, alternatively from
about 1 to about 5 carbon atoms, and further alternatively about 3
carbon atoms; wherein each R' and each R" is independently a
branched or linear carbon chain that may be saturated or
unsaturated (e.g., containing one or more double and/or triple
bonds), and which may have from about 1 to about 4 carbon atoms,
alternatively from about 1 to about 2 carbon atoms, and further
alternatively about 2 carbon atoms; it being understood that one R'
may be the same or different than the other R' group, that one R"
may be the same or different than the other R" group, and that one
or both R' groups may be the same or different than one or both R"
groups. In another embodiment, R may be further characterized as
alkanyl or alkenyl carbon chain having the above-properties. In
other embodiments, R may be characterized as an aromatic carbon
chain or alicyclic carbon chain.
[0097] In a further embodiment, one or more of the carbon chains R
and/or R' of formula (II) may be optionally and independently
derivatized, e.g., the R carbon chain and/or one or more of the R'
and/or R" carbon chains may each contain one or more amino
functional groups, two or more isocyanate functional groups, two or
more epoxy groups, etc.
[0098] Specific examples of siloxane-based compounds include, but
are not limited to, an aqueous solution of alcohol-free aminoalkyl
siloxane such as Silquest.RTM. A-1106 Silane available from
CROMPTON, and an aqueous solution of aminoalkyl siloxane available
from BJ SERVICES as "FSA-1" and from NALCO/EXXON CHEMICALS as
"TEK-STIM 3535".
[0099] In another embodiment, a modifying agent may include one or
more polyisocyanate-based compounds having the following chemical
formula (III):
OCN--R--NCO (III)
[0100] wherein R is at least one of phenyl, derivatized phenyl, or
an aliphatic carbon chain having from about 2 to about 10 carbon
atoms, alternatively having from about 2 to about 6 carbon atoms,
and further alternatively having about 6 carbon atoms.
[0101] In one exemplary embodiment, a polyisocyanate-based
modifying agent may include polyisocyanate-based compounds such as
toluene diisocyanate, heaxamethylene polyisocyanate, etc.
[0102] In another embodiment, a modifying agent may include one or
more epoxy-based compounds having two or more epoxy groups.
[0103] Individual particles of naturally occurring materials may be
strengthened and/or hardened by exposure to a modifying agent using
any wet or dry process suitable for causing interaction between the
modifying agent and one or more compounds present in or on the
natural material in a way that acts to strengthen or harden the
naturally occurring material (e.g., by increasing the elastic
modulus of the naturally occurring material). Exposure
methodologies that are the same as, or that are similar to, resin
coating methods described elsewhere herein (e.g., to coat a first
core material with a second resin material) may also be employed to
expose particles of naturally occurring material to a modifying
agent (e.g., by manufacturers such as FRITZ Industries of Mesquite,
Tex., etc.). Specific examples of suitable exposure methods
include, but are not limited to, by soaking of the naturally
occurring material in a modifying agent (e.g., in one embodiment
using equal parts of modifying agent and naturally occurring
material), by dipping the naturally occurring material in a
modifying agent, by spraying a modifying agent on to the naturally
occurring material (e.g., as particles continuously move through a
pneumatic mover or basket), by mixing naturally occurring
particulate material with liquid, atomized and/or gaseous modifying
agent in a vertical mixer (e.g., as particles continuously move
through a vertical mixer), by flowing modifying agent through a
permeable bed or pack of the naturally occurring particles in a
pressurized container. Drying of particles after exposure may be
accomplished, for example, by continuously dropping through heated
air (e.g., at an elevated temperature of about 375.degree. F.).
[0104] Exposure conditions may be selected and/or varied to enhance
interaction between modifying agent and naturally occurring
material, including selected combinations of temperature and/or
pressure. For example, naturally occurring particulate material may
be raised to an elevated temperature (e.g. from about 100.degree.
F. to about 400.degree. F., alternatively from about 150.degree. F.
to about 375.degree. F.) during or after exposure to a modifying
agent (e.g., using any of the exposure methods described herein) to
facilitate the interaction between a modifying agent and the
particulate material. Besides serving to dry the naturally
occurring material, exposure to an elevated temperature also may
serve to further drive the reaction between the modifying agent and
reactive components of the naturally occurring material, as well as
to burn off softer outer layers of the particles of naturally
occurring material that may be present. However, it will be
understood that heating is not necessary.
[0105] Particles of naturally occurring material may also be
partially or completely impregnated using vacuum and/or pressure
impregnation methods, such as those methods described elsewhere
herein. In one exemplary embodiment, particles of naturally
occurring material may be immersed in a liquid modifying agent in a
sealed container at room temperature, a vacuum (e.g., of from about
-18 to about -20 psi) applied to the container for a period of time
(e.g., about 2 hours), and the particles then separated from the
liquid modifying agent and dried using dry heat (e.g., at an
elevated temperature of about 200.degree. F.). In another exemplary
embodiment, particles of naturally occurring material may be
immersed in a liquid modifying agent in a sealed container at room
temperature, and pressure (e.g., from about 1 psig to about 1000
psig) applied to the container for a period of time (e.g., about 1
hours), and the particles then separated from the liquid modifying
agent and dried using dry heat (e.g., for about 1 hour at an
elevated temperature of about 200.degree. F.). In yet another
exemplary embodiment, combination of vacuum impregnation and
pressure impregnation methods may be employed.
[0106] Particles of a selected naturally occurring material (e.g.,
ground walnut hulls) may be exposed to any amount of a selected
modifying agent effective for strengthening or hardening the
selected naturally occurring material. In this regard, it will be
understood that the amount of modifying agent employed relative to
naturally occurring materials may be varied as necessary to achieve
a desired degree of hardening or strengthening of the naturally
occurring material, for example, to fit conditions of a particular
application (e.g., particular anticipated downhole conditions), to
satisfy cost limitations, etc. It will also be understood that the
amount of modifying agent employed relative to naturally occurring
material may vary according to the number and types of reactive
functional groups present on molecules of the modifying agent. For
example, in one embodiment particles of naturally occurring
material may be exposed to a modifying agent (e.g., silane-based
compound, siloxane-based compound) in an amount of from about
0.001% to about 30% of modifying agent by weight of the particles,
from about 0.001% to about 26% of modifying agent by weight of the
particles, from about 0.001% to about 10% of modifying agent by
weight of the particles, alternatively from about 0.001% to about
2% of modifying agent by weight of the particles, from about 0.001%
to about 1% of modifying agent by weight of the particles,
alternatively from about 0.01% to about 30% of modifying agent by
weight of the particles, from about 0.01% to about 26% of modifying
agent by weight of the particles, from about 0.01% to about 10% of
modifying agent by weight of the particles, alternatively from
about 0.01% to about 2% of modifying agent by weight of the
particles, from about 0.01% to about 1% of modifying agent by
weight of the particles, alternatively from about 0.1% to about 30%
of modifying agent by weight of the particles, from about 0.1% to
about 26% of modifying agent by weight of the particles, from about
0.1% to about 10% of modifying agent by weight of the particles,
alternatively from about 0.1% to about 2% of modifying agent by
weight of the particles, from about 0.1% to about 1% of modifying
agent by weight of the particles, alternatively from about 1% to
about 2% of modifying agent by weight of the particles.
[0107] In an alternative and exemplary embodiment, particles of
naturally occurring material (e.g., ground walnut hulls) may be
introduced into a vertical mixer, heated to a temperature of from
about 100 to about 400.degree. F. and sprayed or otherwise exposed
to a modifying agent. For example, ground walnut hulls may be
exposed to a siloxane-based compound (e.g., FSA-1) in an amount of
about 26% of modifying agent by weight of naturally occurring
particulate material. It will be understood that the foregoing
ranges of modifying agent amount are exemplary only, and that
particles of naturally occurring materials may be exposed to
modifying agent/s in other amounts (e.g., including up to and
greater than about 100% of modifying agent by weight of the
particles). For example, by soaking particles of naturally
occurring material in a suitable modifying agent in conjunction
with vacuum and/or pressure impregnation, exposure values of from
about 0.1% to about 30% alternatively about 10% of modifying agent
by weight of naturally occurring particulate material may be
achieved.
[0108] Modifying agents may be diluted as so desired in a suitable
solvent prior to treating particles of a naturally occurring
material. Examples of solvent materials with which modifying agents
may be diluted include low surface tension solvents. Specific
examples of suitable diluting materials include, but are not
limited to, ethylene glycol monobutylether ("EGMBE"), alcohols
(e.g., methanol, ethanol, etc.), water-based solvents mixed with
low surface tension surfactants (e.g., fluro-surfactants, etc.),
organic fluids such as diesel, etc.
[0109] Effectiveness of modifying agents may be optionally
enhanced, for example, by facilitating interaction between a
modifying agent and one or more components present in a naturally
occurring material. In this regard interaction between a modifying
agent and components present in a naturally occurring material may
be facilitated using one or more enhancing agents (e.g., swelling
agents, penetrating agents, etc.) and/or by exposing a naturally
occurring material to one or more enhancing conditions such as
described above that serve to enhance interaction with a modifying
agent (e.g., vacuum and/or pressure impregnation). Examples of
suitable enhancing agents include, but are not limited to, liquid
or gaseous ammonia, dimethyl sulfoxide ("DMSO"), methyl
pyrrolidone, etc. While not wishing to be bound by theory, it is
believed that such enhancing agents act to facilitate interaction
between a modifying agent and one or more components present in the
naturally occurring material (e.g., natural resins, lignins and/or
cellulosic fibers) by opening the matrix (e.g., by causing
swelling) of the matrix of the naturally occurring material or
otherwise penetrating through the matrix of the naturally occurring
material to allow deeper penetration by the modifying agent. By
facilitating interaction between modifying agent and naturally
occurring material, an enhancing agent may make possible the use of
less modifying agent relative to naturally occurring particulate
material to produce the same or substantially the same results,
reducing cost of treatment.
[0110] In one embodiment, selection of appropriate enhancing agent
may be made based on compatibility with selected modifying agent.
For example, ammonia may be more desirable for use as an enhancing
agent when employed with silane-based or siloxane-based modifying
agent than with polyisocyanate-based modifying agents, due to low
affinity of silane-based and siloxane-based modifying agents for
nitrogen atoms relative to polyisocyanate-based modifying agents.
In another example, DMSO may be desirable for use as an enhancing
agent in conjunction with polyisocyanate-based modifying agents.
However, it will be understood that any desired combination of one
or more enhancing agent/s and one or more modifying agent/s may be
employed to produce modified naturally occurring particulate
material having desired characteristics (e.g., strength, hardness,
resistance to deformation, etc.) to fit a given application.
[0111] Individual particles of naturally occurring materials may be
exposed to one or more enhancing agent/s using any methodology
suitable for facilitating interaction between the particles of
naturally occurring materials and one or more modifying agents to
which the naturally occurring material may be exposed. In this
regard, particles of naturally occurring material may be exposed to
one or more enhancing agents prior to, simultaneously with, and/or
after exposure to one or more modifying agents as long as the
enhancing agent acts to facilitate interaction between the
modifying agent/s and the naturally occurring material
particulates. Exposure of naturally occurring particulate material
to enhancing agent may be accomplished using any method suitable
for contacting the particles with the enhancing agent/s including,
for example, the same methods described above for exposing
naturally occurring particulate material to a modifying agent,
e.g., coating, soaking, dipping, spraying, mixing, flowing, etc.
Furthermore, vacuum and/or pressure impregnation, and/or elevated
temperatures may be also be employed where applicable and desired
to increase effectiveness of an enhancing agent.
[0112] In one exemplary embodiment, particles of naturally
occurring particulate material (e.g., ground walnut hulls) may be
placed in a container through which liquid or gaseous enhancing
agent (e.g., liquid, atomized or gaseous amnonia) is flowed to
expose the particulate material to the enhancing agent. Following
and/or during exposure to the enhancing agent, the particulate may
be exposed to liquid, atomized or gaseous modifying agent/s (e.g.,
gamma-aminopropyltriethoxy silane) in the same container by flowing
the modifying agent though the container in a manner similar to the
enhancing agent. Alternatively, the particulate may be removed from
the container and exposed to modifying agent/s using a separate
exposure step, such as by coating, soaking, spraying, etc. In
another exemplary embodiment, particles of naturally occurring
particulate material (e.g., ground walnut hulls) may be introduced
into a vertical mixer through which atomized or gaseous enhancing
agent (e.g., atomized or gaseous ammonia) is flowed to expose the
particulate material to the enhancing agent. Following and/or
during exposure to the enhancing agent, the particulate may be
exposed to atomized or gaseous modifying agent/s (e.g.,
gamma-aminopropyltriethoxy silane) in the same mixer by flowing the
modifying agent though the mixer in a manner similar to the
enhancing agent. Alternatively, the particulate may be removed from
the mixer for exposure to modifying agent/s in a separate exposure
step as described immediately above.
[0113] Following treatment with modifying agent (with or without
optional enhancing agent), particles of naturally occurring
material may be employed as proppant and/or sand control particles
in any of the embodiments described elsewhere herein. In one
embodiment, particles of a modified naturally occurring material
may be utilized as relatively lightweight particulate/proppant
materials. In such an embodiment, amounts and type of modifying
agent may be selected so that the ASG of a naturally occurring
particulate material may be affected relatively little, if at all,
by treatment with a modifying agent. For example, the ASG of ground
walnut hulls treated with about 26% by weight of an
aminopropyltriethoxy silane modifying agent may be changed from
about 1.2 to about 1.3. Such modified ground walnut hull
particulate material may be introduced or pumped into a well as
neutrally buoyant particles in a carrier fluid that may be, for
example, a 11.5 pound per gallon (ppg) brine.
[0114] In one embodiment, particles of a modified naturally
occurring material may be utilized as particulate/proppant material
suitable for use at more severe or demanding downhole conditions
(e.g., at higher downhole temperatures and/or under higher downhole
conditions of closure stress) than the conditions under which
particles of the same, but un-modified, naturally occurring
material may be suitably employed. For example, in one exemplary
embodiment modified particulate material may be formulated as
described herein and introduced or pumped (e.g., as neutrally
buoyant proppant and/or sand control particulate) in any suitable
carrier fluid (e.g., saturated sodium chloride solution carrier
fluid or other completion or workover brine) into a well for
exposure to downhole temperatures of greater than or equal to about
170.degree. F., alternatively greater than or equal to about
200.degree. F., alternatively greater than or equal to about
225.degree. F., alternatively greater than or equal to about
250.degree. F., alternatively greater than or equal to about
270.degree. F. In another exemplary embodiment, modified
particulate material may be formulated as described herein and
introduced or pumped into a well for exposure to downhole
temperatures of up to about 200.degree. F., alternatively up to
about 225.degree. F., alternatively up to about 250.degree. F.,
alternatively up to about 270.degree. F., and further alternatively
up to about 300.degree. F. In another exemplary embodiment,
modified particulate material may be formulated as described herein
and introduced or pumped into a well for exposure to downhole
temperatures of from about 100.degree. F. to about 300.degree. F.,
alternatively from about 170.degree. F. to about 300.degree. F.,
alternatively from about 200.degree. F. to about 300.degree. F.,
alternatively from about 225.degree. F. to about 300.degree. F.,
alternatively from about 250.degree. F. to about 300.degree. F.,
alternatively from about 270.degree. F. to about 300.degree. F.,
and further alternatively from about 150.degree. F. to about
250.degree. F.
[0115] In another exemplary embodiment, modified particulate
material may be so introduced into a well for exposure to closure
stresses of greater than or equal to about 4,000 psi, alternatively
of greater than or equal to about 5000 psi, alternatively of
greater than or equal to about 6000 psi, alternatively of greater
than or equal to about 8000 psi, alternatively of greater than or
equal to about 10,000 psi, alternatively of from about 4000 psi to
about 10,000 psi, alternatively from about 5,000 psi to about 6000
psi, alternatively from about 5000 psi to about 8,000 psi,
alternatively from about 5000 psi to about 10,000 psi. In another
exemplary embodiment, modified particulate material may be so
introduced into a well for exposure to closure stresses of up to
about 5000 psi, alternatively up to about 6000 psi, alternatively
up to about 8000 psi, alternatively up to about 10,000 psi,
alternatively from about 1000 psi to about 4000 psi, alternatively
from about 1000 psi to about 5000 psi, alternatively from about
1000 psi to about 6000 psi, further, alternatively from about 1000
psi to about 8000 psi, further alternatively from about 1000 psi to
about 10,000 psi. It will be understood that these ranges of
temperature and closure stress are exemplary only, and that the
disclosed modified particulate materials may be employed as
proppant and/or sand control materials at temperatures greater than
or equal to about 300.degree. F. and/or at closure stresses greater
than or equal to about 10,000 psi, and that combinations of
particular naturally occurring materials, particular modifying
agents, particular enhancing agents and/or manufacturing conditions
may be selected based on the teaching of the disclosure herein to
meet and withstand anticipated downhole conditions of a given
application.
[0116] Naturally occurring particulate material that has been
treated with modifying agent may be employed as relatively
lightweight particulate/proppant material without further
treatment. However, modified particles of naturally occurring
material may also be coated or at least partially surrounded with
at least one layer of a second material (e.g., resin, epoxy, etc.)
that may be selected to act to harden and/or isolate or protect the
first material from adverse formation or wellbore conditions in a
manner as described below.
[0117] In one embodiment, a multi-component relatively lightweight
and/or substantially neutrally buoyant proppant/sand control
particle may include a first material and at least one additional,
or second, different material. The first material and at least one
second material may have different values of in situ Young's
modulus and/or be of differing composition. Alternatively, the
first material and at least one second material may have similar or
same values of in situ Young's modulus and/or be of similar or same
composition. At least one of the first or second materials may
optionally be a naturally occurring material that has been modified
by exposure to one or more modifying agents and/or enhancing
agents.
[0118] In one embodiment, a second material may be present as a
protective layer around a first material core, as described further
herein. In another embodiment, a second material may be present to
alter the overall modulus of a particulate formed therefrom, such
as to function as a hardening material. For example, overall in
situ Young's modulus of modified or unmodified ground walnut hulls
may be increased by coating such particles with a layer of
relatively hard resin having a higher in situ Young's modulus. A
single material may be present to perform both protective and
hardening functions, or separate materials may be present to
perform each of these respective functions. As used herein, a
"layer" refers to a second material that at least partially or
completely surrounds a first core material. A layer includes
materials that adhere to or are otherwise disposed on the surface
of a core material, and/or to those materials that are at least
partially absorbed or permeated into a first core material.
[0119] In one embodiment, the two or more materials may be
configured in virtually any manner desired to form multi-component
particles (for example, as described elsewhere herein) to achieve
varying overall density and/or hardness characteristics (or in situ
Young's modulus) of such particles, for example, to meet specific
formation conditions.
[0120] In another embodiment, a first relatively lightweight and/or
substantially neutrally buoyant core material may be coated or at
least partially surrounded with at least one layer of a second
material that may be selected to act to harden and/or isolate or
protect the first material from adverse formation or wellbore
conditions, for example so as to avoid exposure to acids or other
workover/drilling fluids, to avoid saturation with liquids, provide
longer fracture proppant/sand control pack life, etc. In this
regard, any coating material known in the art and suitable for
imparting hardness and/or suitable for at least partially
protecting or isolating a first relatively lightweight and/or
substantially buoyant core material as so described herein may be
employed. Examples of such hardening and/or protective materials
include, but are not limited to resins (e.g., urethane, phenolic,
melamine formaldehyde, etc.) described for other use in other
embodiments elsewhere herein. With benefit of this disclosure,
suitable coating material/s may be selected by those of skill in
the art to achieve or impart the desired qualities to a first
relatively lightweight and/or substantially buoyant core material,
considering anticipated wellbore and/or formation conditions.
Methods for coating particulates (e.g., fracture proppant
particles, etc.) with materials such as resin are known in the art,
and such materials are available, for example, from manufacturers
listed herein. With regard to coating of the disclosed lightweight
and/or substantially neutrally buoyant materials, coating
operations may be performed using any suitable methods known in the
art. For example, low temperature curing methods may be employed if
desired (e.g., using fast setting "cold set" or "cold cure"
resins), where heating may be a problem, such as when coating
materials which may be sensitive to heat, like ground nuts or fruit
pits. Alternatively, indirect heating processes may be employed
with such materials when it is necessary to heat a coating material
for cure.
[0121] Examples of resins that may be employed as layers for
protective and/or hardening purposes include, but are not limited
to, phenol formaldehyde resins, melamine formaldehyde resins, and
urethane resins, low volatile urethane resins (e.g., these and
other types of resins available from BORDEN CHEMICAL INC., SANTROL,
HEPWORTH of England), etc., and mixtures thereof. Specific examples
of suitable resins include, but are not limited to, resins from
BORDEN CHEMICAL and identified as 500-series and 700-series resins
(e.g., 569C, 794C, etc.). Further specific examples of resins
include, but are not limited to, "SIGMASET" series low temperature
curing urethane resins from BORDEN CHEMICAL (e.g., "SIGMASET",
"SIGMASET LV", "SIGMASET XL"), "ALPHASET" phenolic resin from
BORDEN, "OPTI-PROP" phenolic resin from SANTROL, and "POLAR PROP"
low temperature curing resin from SANTROL. Low temperature curing
resins may be applied with little or no heat, which may be
desirable when coating heat-sensitive materials such as wood, nut
shell material, etc. Alternatively, heat cured resins may be
applied and cured using heating methods that are compatible with
heat sensitive materials. For example, in one embodiment, ground
walnut shells may be coated with SANTROL "OPTI-PROP" resin in a
single coating step using indirect heat (e.g., at temperatures of
up to about 300.degree. F., or alternatively from about 150.degree.
F. to about 200.degree. F.). Where desired, curing characteristics
(e.g., curing time, etc.) may be adjusted to fit particular layer
application methods and/or final product specifications by, for
example, adjusting relative amounts of resin components. Still
further examples of suitable resins and coating methods include,
but are not limited to, those found in European Patent Application
EP 0 771 935 A1; and in U.S. Pat. Nos. 4,869,960; 4,664,819;
4,518,039; 3,929,191; 3,659,651; and 5,422,183, each of the
foregoing references being incorporated herein by reference in its
entirety.
[0122] With benefit of this disclosure, those of skill in the art
will understand that first and one or more second materials may be
selected to meet particular criteria based on the information and
examples disclosed herein, as well as knowledge in the art. In this
regard, one or more second material coatings or layers may be
present, for example, to substantially protect the ground walnut
hull first material from downhole fluids such as formation,
drilling, workover fluids (e.g., salt water, acid, etc.), and/or to
harden or otherwise modify the first material from closure stress
or other mechanical stresses that may be encountered downhole. In
this regard, thickness or amount of one or more coatings may be any
amount suitable to provide a particle having an altered in situ
Young's modulus and/or to provide at least partial protection, for
the inner first material, from wellbore or formation
conditions.
[0123] In one embodiment, a coating of one or more second materials
may be from about 0.1% by weight to about 50%, alternatively from
about 1% by weight to about 20% by weight, alternatively from about
10% by weight to about 20%, alternatively from about 2% to about
12% by weight of the total weight of the multi-component particle,
although greater and lesser amounts are possible. In this way, a
first material such as ground walnut shell particulates may be
coated with, for example, from about 2% to about 12% of a suitable
resin (e.g., BORDEN "SIGMASET LV" resin) by weight of total weight
of each particle to form relatively lightweight and/or
substantially neutrally buoyant proppant/sand control particulate.
Such particles may exhibit increased strength and/or resistance to
well fluids over uncoated ground walnut hulls. In one embodiment,
it has been found that application of from about 8% to about 12% by
weight of total particle weight of "SIGMASET LV" resin to ground
walnut hull particulate material serves to permeate the material so
as to substantially fill the accessible or permeable porosity of
the materials such that a relatively shiny or glazed surface
appearance is achieved.
[0124] In one exemplary embodiment, about 12/20 mesh ground walnut
hulls from "COMPOSITION MATERIALS, INC." having an in situ Young's
modulus of from about 1,000,000 psi to about 2,000,000 psi (and
described elsewhere herein) may be coated with a second material,
such as "SIGMASET LV" or "SIGMASET XL" resin available from BORDEN
CHEMICAL (in amounts as described elsewhere herein). Such coated
particles may be manufactured and/or supplied, for example, by
BORDEN CHEMICAL. It will be understood that a protective resin
layer may also function as a hardener to the core material,
however, an additional and separate hardener material layer may
also be present to impart additional hardness to the core material
if so desired. In one exemplary embodiment in which such a separate
hardener layer is present, ground walnut shell particulates may be
first coated with from about 2% to about 10% by weight (and
alternatively about 2% by weight) of total weight of a separate
hardener material (e.g., BORDEN "2AC" hardener) and then coated
with from about 1% to about 20% by weight (and alternatively about
4% by weight) of another resin (e.g., BORDEN "SIGMASET XL" or
"SIGMASET LV" resin). In one exemplary embodiment then, the 12/20
mesh ground walnut shells described above may be coated with about
2% by weight of total weight of BORDEN "2AC" hardener and about 4%
by weight of total weight of BORDEN "SIGMASET XL."
[0125] It will be understood that the coating amounts given herein
are exemplary only, and may be greater or lesser, and that amounts
and types of core, separate hardener material and/or other
protective layer material/s may be selected with benefit of this
disclosure by those of skill in the art to meet or and withstand
anticipated downhole conditions of a given application using
methods known in the art, such as those described herein (e.g., in
Examples 1 and 2). For example, in the embodiment above, ground
walnut shell particles having about 2% by weight "SIGMASET XL" may
be employed for relatively lower closure stress applications (such
as some sand control applications), and ground walnut shell
particles having closer to about 10% by weight "SIGMASET XL" may be
employed for relatively higher closure stress applications (such as
a proppant or fracture pack particulate), although it will be
understood that these are exemplary guidelines only.
[0126] In one embodiment, the second material coating may be
present, for example, to substantially protect the ground walnut
hull first material from downhole fluids such as formation,
drilling, workover fluids (e.g., salt water, acid, etc.), while at
the same time altering the in situ Young's modulus of the particles
from a starting value of about 1,000,000 psi to about 2,000,000
psi, to an overall value of from about 2,000,000 to about 3,000,000
psi.
[0127] In another exemplary embodiment, ground walnut hulls (or
another porous first material) may be partially or completely
impregnated with a second material, by for example, vacuum and/or
pressure impregnation, spraying with hardener, or a combination
thereof. For example, material may be immersed in a second material
and then exposed to pressure and/or vacuum to impregnate the
material. Such methods are known in the art for impregnating porous
materials, such as impregnating core samples with fluids, etc.
Alternatively, application of a second material may result in at
least partial impregnation, for example, it has been found that up
to about 10% to about 12% by weight of total particle weight of
resin (such as BORDEN "SIGMASET XL") may be applied and penetrate
into the porosity of ground walnut shells. Furthermore, it will be
understood that a first relatively lightweight and/or substantially
buoyant material may be combined with more than one other material,
e.g., using the methods and configurations described elsewhere
herein for embodiments involving first and second materials.
[0128] It will be understood with benefit of the disclosure that
any other material suitable for coating a substantially hard
proppant or sand control particulate core and having suitable
protective, hardening, and/or specific gravity-altering
characteristics as defined elsewhere herein may be employed.
[0129] Porous Particulate Treated with Non-Porous Material
[0130] The relatively lightweight and/or substantially neutrally
buoyant proppant or sand control particulate may further be a
selectively configured porous particulate materials as well as a
non-selectively configured porous particulate material.
[0131] The porous particulate material shall include any naturally
occurring or manufactured or engineered porous ceramic particulate
material that has an inherent and/or induced porosity. A
commercially available instrument, ACCUPYC 1330 Automatic Gas
Pycnometer (Micromeritics, Norcross, Ga.), that uses helium as an
inert gas and the manufacturer's recommended procedure can be used
to determine the internal porosity of the particulates. The
internal porosity is generally from about 10 to 75 volume percent.
Such particulate material may also have an inherent or induced
permeability, i.e., individual pore spaces within the particle are
interconnected so that fluids are capable of at least partially
moving through the porous matrix, such as penetrating the porous
matrix of the particle, or may have inherent or induced
non-permeability, individual pore spaces within the particle are
disconnected so that fluids are substantially not capable of moving
through the porous matrix, such as not being capable of penetrating
the porous matrix of the particle. The degree of desired porosity
interconnection may be selected and engineered into the
non-selectively configured porous particulate material. Furthermore
such porous particles may be selected to have a size and shape in
accordance with typical fracturing proppant particle specifications
(i.e., having a uniform shape and size distribution), although such
uniformity of shape and size is not necessary.
[0132] The ASG of the porous particulate material is generally less
than or equal to 2.4, preferably less than or equal to 2.0, even
more preferably less than or equal to 1.75, most preferably less
than or equal to 1.25.
[0133] In a selectively configured porous particulate material, the
particles may be selected based on porosity and/or permeability
characteristics so that they have desired lightweight
characteristics, such as when suspended in a selected carrier fluid
for a well treatment. As before, the inherent and/or induced
porosity of a porous material particle may be selected so as to
help provide the desired balance between apparent density and
strength. Optional materials may be employed along with a glazing,
penetrating and/or coating material to control penetration, such as
enhancing or impairing penetration. For example, in one embodiment
a cationic clay stabilizer, such as CLAY MASTER 5C from BJ
Services, may be first applied to the exterior surface of a porous
ceramic material to inhibit penetration by coating/penetrating
material, such as epoxy or resin described elsewhere herein.
[0134] Examples of non-natural porous particulate materials for use
in the invention include, but are not limited to, porous ceramic
particles such as those particles available from Carbo Ceramics
Inc. as "Econoprop", and those fired kaolinitic described in U.S.
Pat. No. 5,188,175 which is incorporated herein by reference. As
described in this reference such particles may include solid
spherical pellets or particles from raw materials (such as kaolin
clay) having an alumina content of between about 25% and 40% and a
silica content of between about 50% and 65%. A starch binder may be
employed. Such particles may be characterized as having a ratio of
silicon dioxide to alumina content of from about 1.39 to about
2.41, and an ASG of between about 2.20 and about 2.60 or between
about 2.20 and about 2.70.
[0135] It will also be understood that porous ceramic particles may
be selectively manufactured from raw materials such as those
described in U.S. Pat. No. 5,188,175; U.S. Pat. No. 4,427,068; and
U.S. Pat. No. 4,522,731, which are each incorporated herein by
reference, such as by inclusion of selected process steps in the
initial material manufacturing process to result in a material that
possesses desired characteristics of porosity, permeability,
apparent density or ASG, and combinations thereof. For example,
such raw materials may be fired at relatively low temperature of
about 1235.degree. F. or about 1300.degree. F. (or about
700.degree. C.) to achieve a desired crystalline structure and a
more highly porous and lighter structure. In one exemplary
embodiment of such particles, as described elsewhere herein, about
20/40 mesh size porous material fired kaolinitic particles from
Carbo Ceramics Inc. may be selected for use in the disclosed
method. These particles have the following internal
characteristics: bulk apparent density about 1.16, internal
porosity about 59.3%. These particles may be treated with a variety
of penetrating/coating materials in an amount of from about 0.5 to
about 10% by total weight of particle.
[0136] In such a case, the particles may be selected based on
porosity and/or permeability characteristics so that they have
desired lightweight characteristics, such as when suspended in a
selected carrier fluid for a well treatment. As before, the
inherent and/or induced porosity of a porous material particle may
be selected so as to help provide the desired balance between ASG
and strength. Optional materials may be employed along with a
glazing, penetrating and/or coating material to control penetration
such as enhance or impair penetration. For example, in one
embodiment an cationic clay stabilizer, such as CLAY MASTER 5C from
BJ Services, may be first applied to the exterior surface of a
porous ceramic material to inhibit penetration by
coating/penetrating material, such as epoxy or resin described
elsewhere herein.
[0137] In a selectively configured porous particulate material, the
porous particulate material is chemically treated in order to
impart desired physical properties, such as porosity, permeability,
apparent density or ASG, or combinations thereof to the particulate
materials. Such desired physical properties are distinct from the
physical properties of the porous particulate materials prior to
treatment.
[0138] The desired physical properties may further be present in
non-selectively configured porous particulate materials.
Non-selectively configured porous particulate materials shall
include naturally occurring porous ceramic materials as well as
non-natural (synthetic) materials manufactured in a manner that
renders such desired characteristics.
[0139] The non-selectively configured particulate material is
selected based on desired physical properties, such as porosity,
permeability, apparent density, particle size, chemical resistance
or combinations thereof.
[0140] Such desired physical properties may be imparted to a
portion or portions of the porous particulate material of the
selectively configured porous particulate material or
non-selectively configured porous particulate material, such as on
the particle surface of the material particulate, at or in the
particle surface of the particulate material, in an area near the
particle surface of a particulate material, in the interior
particle matrix of a particulate material or a portion thereof,
combinations thereof, etc.
[0141] The ASG of the selectively configured porous particulate, as
well as non-selectively configured porous particulate, is generally
less than or equal to 2.4 to meet the pumping and/or downhole
formation conditions of a particular application, such as hydraulic
fracturing treatment, sand control treatment.
[0142] Advantageously, in one embodiment the low ASG of the porous
particulate material of the selectively configured porous
particulate material or non-selectively configured porous
particulate material may be taken advantage of to result in a
larger fracture or frac pack width for the same loading, such as
pound per square foot of proppant, to give much larger total volume
and increased width for the same mass. Alternatively, this
characteristic allows for smaller loading of proppant material to
be pumped while still achieving an equivalent width.
[0143] In a preferred embodiment, selective configuration, such as
by using glaze-forming, coating and/or penetrating materials, such
as those materials described elsewhere herein, may be selectively
employed to modify or customize the ASG of a selected porous
particulate material. Modification of particulate ASG, to have a
greater or lesser ASG, may be advantageously employed, for example,
to provide proppant or sand control particulates of customized ASG
for use as a substantially neutrally buoyant particulate with a
variety of different weight or ASG carrier fluids.
[0144] The selectively configured porous particulate material may
comprise porous particulate material selectively altered by
treating with a coating or penetrating material using any suitable
wet or dry process. Methods for coating particulates, such as
fracture proppant particles, with materials such as resin are known
in the art, and such materials are available, for example, from
manufacturers listed herein. With regard to coating of the
disclosed porous particulate materials, coating operations may be
performed using any suitable methods known in the art.
[0145] As used herein, the term "penetration" shall further refer
to partially or completely impregnated with a penetrating material,
by for example, vacuum and/or pressure impregnation. For example,
porous particulate material may be immersed in a second material
and then exposed to pressure and/or vacuum to at least partially
penetrate or impregnate the material.
[0146] Those of skill in the art will understand that one or more
coating and/or penetrating materials may be selected to treat a
porous material particulate to meet particular criteria or
requirements of given downhole application based on the information
and examples disclosed herein, as well as knowledge in the art. In
this regard, porous material particle characteristics, such as
composition, porosity and permeability characteristics of the
particulate material, size, and/or coating or penetrating material
characteristics, such as composition, amount, thickness or degree
of penetration, may be so selected. The coating or penetrating
material is typically non-porous.
[0147] The porosity and permeability characteristics of the porous
particulate material allows the penetrating material to be drawn at
least partially into the porous matrix of the porous particulate
material by capillary action, for example, in a manner similar to a
sponge soaking up water. Alternatively, one or more penetrating
materials may be drawn at least partially into the porous matrix of
the porous particulate material using a vacuum, and/or may be
forced at least partially into the porous matrix under
pressure.
[0148] Examples of penetrating materials that may be selected for
use include, but are not limited to, liquid resins, plastics,
cements, sealants, binders or any other material suitable for at
least partially penetrating the porous matrix of the selected
particle to provide desired characteristics of strength/crush
resistance, ASG, etc. It will be understood that selected
combinations of any two or more such penetrating materials may also
be employed, either in mixture or in sequential penetrating
applications.
[0149] Examples of resins that may be employed as penetrating
and/or coating materials include, but are not limited to, resins
and/or plastics or any other suitable cement, sealant or binder
that once placed at least partially within a selected particle may
be crosslinked and/or cured to form a rigid or substantially rigid
material within the porous structure of the particle. Specific
examples of plastics include, but are not limited to, nylon,
polyethylene, styrene, etc. and combinations thereof. Suitable
resins include phenol formaldehyde resins, melamine formaldehyde
resins, and urethane resins, low volatile urethane resins, such as
these and other types of resins available from Borden Chemical
Inc., Santrol, Hepworth of England, epoxy resins and mixtures
thereof. Specific examples of suitable resins include, but are not
limited to, resins from Borden Chemical and identified as
500-series and 700-series resins (e.g., 569C, 794C, etc.). Further
specific examples of resins include, but are not limited to,
SIGMASET series low temperature curing urethane resins from Borden
Chemical, such as SIGMASET, SIGMASET LV, SIGMASET XL, ALPHASET
phenolic resin from Borden Chemical, OPTI-PROP phenolic resin from
Santrol, and POLAR PROP low temperature curing resin from Santrol.
Where desired, curing characteristics, such as curing time, may be
adjusted to fit particular treatment methods and/or final product
specifications by, for example, adjusting relative amounts of resin
components. Still further examples of suitable resins and coating
methods include, but are not limited to, those found in European
Patent Application EP 0 771 935 A1; and in U.S. Pat. Nos.
4,869,960; 4,664,819; 4,518,039; 3,929,191; 3,659,651; and
5,422,183, each of the foregoing references being incorporated
herein by reference in its entirety.
[0150] In one exemplary embodiment, a curable phenolic resin or
other suitable curable material may be selected and applied as a
coating material so that individual coated particles may be bonded
together under downhole temperature, after the resin flows and
crosslinks/cures downhole, such as to facilitate proppant pack/sand
control particulate consolidation after placement.
[0151] Alternatively, a cured phenolic type resin coat or other
suitable cured material may be selected to contribute additional
strength to the particles and/or reduce in situ fines migration
once placed in a subterranean formation. The degree of penetration
of the coating or penetrating fluid into the porous particulate
material may be limited by disconnected porosity, such as
substantially impermeable or isolated porosity, within the interior
matrix of the particulate.
[0152] This may either limit the extent of uniform penetration of
penetrating material in a uniform manner toward the core, such as
leaving a stratified particle cross section having outside
penetrating layer with unpenetrated substantially spherical core,
and/or may cause uneven penetration all the way to the core, such
as bypassing "islands" of disconnected porosity but penetrating all
the way to the core. In any event, a penetrating and/or coating
material may trap or encapsulate air (or other fluid having ASG
less than particle matrix and less than coating/penetrating
material) within the disconnected porosity in order to reduce ASG
by the desired amount. Such materials coat and/or penetrate the
porous particulate without invading the porosity to effectively
encapsulate the air within the porosity of the particle.
Encapsulation of the air provides preservation of the
ultra-lightweight character of the particles once placed in the
transport fluid. If the resin coating or transport fluids were to
significantly penetrate the porosity of the particle, the density
increases accordingly, and the particle no longer has the same
lightweight properties. The resin coat also adds strength and
substantially enhances the proppant pack permeability at elevated
stress.
[0153] Coating layers may be applied as desired to contribute to
particle strength and/or reduce in situ fines migration once placed
in a subterranean formation. The coating significantly increases
the strength and crush resistance of the ultra-lightweight ceramic
particle. In the case of natural sands the resin coat protects the
particle from crushing, helps resist embedment, and prevents the
liberation of fines.
[0154] The coating or penetrating fluid is typically selected to
have an ASG less than the ASG of the porous particulate material so
that once penetrated at least partially into the pores of the
matrix it results in a particle having a ASG less than that of the
porous particulate material prior to coating or penetration, i.e.,
filling the pore spaces of a porous particulate material results in
a solid or substantially solid particle having a much reduced
apparent density.
[0155] For example, the selected porous particulate material may be
treated with a selected penetrating material in such a way that the
resultant selectively configured porous particulate material has a
much reduced ASG, such as having an ASG closer to or approaching
the ASG of a carrier fluid so that it is neutrally buoyant or
semi-buoyant in a fracturing fluid or sand control fluid.
[0156] Alternatively, a penetrating material may be selected so
that it helps structurally support the matrix of the porous
particulate material (i.e., increases the strength of the porous
matrix) and increases the ability of the particulate to withstand
the closure stresses of a hydraulic fractured formation, or other
downhole stresses.
[0157] For example, a penetrating material may be selected by
balancing the need for low ASG versus the desire for strength,
i.e., a more dense material may provide much greater strength. In
this regard, the inherent and/or induced porosity of the porous
particulate material may be selected so as to help provide the
desired balance between ASG and strength. It will be understood
that other variable, such as downhole temperature and/or fluid
conditions, may also impact the choice of penetrating
materials.
[0158] The coating layer or penetrating material is generally
present in the selectively configured porous particulate material
in an amount of from about 0.5% to about 10% by weight of total
weight. The thickness of the coating layer of the selectively
configured porous particulate material is generally between from
about 1 to about 5 microns. The extent of penetration of the
penetrating material of the selectively configured porous
particulate material is from less than about 1% penetration by
volume to less than about 25% penetration by volume.
[0159] Especially preferred results are obtained when the porous
particulate material is a porous ceramic particle having an ASG of
1.25 or less and untreated porosity is approximately 60%. Such
materials may be treated with a coating material that does not
penetrate the porous matrix of the porous particulate material, or
that only partially penetrates the porous matrix of the ceramic
particulate material. Such treated ceramic materials may have an
ASG from about 1.1 to about 1.8 (alternatively from about 1.75 to
about 2.0, and further alternatively about 1.9), a bulk ASG from
about 1.03 to about 1.5, and a treated internal porosity from about
10% to about 75% volume. However, values outside these exemplary
ranges are also possible.
[0160] As an example, a porous ceramic treated with about 6% epoxy
has been seen to exhibit a bulk ASG of about 1.29 and a porosity of
about 50.6%, a porous ceramic treated with about 8% epoxy exhibits
a bulk ASG of about 1.34 and a porosity of about 46.9%, a porous
ceramic treated with about 6% phenol formaldehyde resin exhibits a
bulk ASG of about 1.32 and a porosity of about 51.8%, and a porous
ceramic treated with about 8% phenol formaldehyde resin exhibits a
bulk ASG of about 1.20 and a porosity of about 54.1%.
[0161] In this embodiment, a coating material or penetrating
material may be selected to be present in an amount of from about
0.5% to about 10% by weight of total weight of individual
particles. When present, thickness of a coating material may be
selected to be from about 1 to about 5 microns on the exterior of a
particle. When present, extent of penetration penetrating material
into a porous material particle may be selected to be from less
than about 1% penetration by volume to less than about 25%
penetration by volume of the particle. It will be understood that
coating amounts, coating thickness, and penetration amounts may be
outside these exemplary ranges as well.
[0162] Further, the porous particulate material may be at least
partially selectively configured by glazing, such as, for example,
surface glazing with one or more selected non-porous glaze
materials. In such a case, the glaze, like the coating or
penetrating material, may extend or penetrate at least partially
into the porous matrix of the porous particulate material,
depending on the glazing method employed and/or the permeability
(i.e., connectivity of internal porosity) characteristics of the
selected porous particulate material, such as non-connected
porosity allowing substantially no penetration to occur. For
example, a selected porous particulate material may be selectively
configured, such as glazed and/or coated with a non-porous
material, in a manner so that the porous matrix of the resulting
particle is at least partially or completely filled with air or
some other gas, i.e., the interior of the resulting particle
includes only air/gas and the structural material forming and
surrounding the pores. Once again, the inherent and/or induced
porosity of a porous material particle may be selected so as to
help provide the desired balance between apparent density and
strength, and glazing and/or coating with no penetration (or
extension of configured area into the particle matrix) may be
selected to result in a particle having all or substantially all
porosity of the particle being unpenetrated and encapsulated to
trap air or other relatively lightweight fluid so as to achieve
minimum ASG. In addition to sealing a particle, such as to seal
air/gas within the porous matrix of the particle, such selective
configuration, such as using glazing and/or coating materials, may
be selected to provide other advantages.
[0163] In a preferred embodiment, the porous particulate material,
such as the above-described fired kaolinitic particles, is
manufactured by using a glaze-forming material to form a glaze to
seal or otherwise alter the permeability of the particle surface,
so that a given particle is less susceptible to invasion or
saturation by a well treatment fluid and thus capable of retaining
relatively lightweight or substantially neutrally buoyant
characteristics relative to the well treatment fluid upon exposure
to such fluid. Such glazing may be accomplished using any suitable
method for forming a glaze on the surface or in the near surface of
a particle, including by incorporating a glaze-forming material
into the raw material "green paste" that is then formed such as
molded into shape of the particle prior to firing. Those skilled in
the art recognize that glazes may be made from a variety of
methods, including the application of a smooth, glassy coating such
that a hard, nonporous surface is formed. Glazes may be formed from
powdered glass with oxides. The mixture of powders is suspended in
water and applied to the substrate. The glaze can be dried and then
fixed onto the substrate by firing or similar process known to
those skilled in the art. Additionally, the use of borates or
similar additives may improve the glaze.
[0164] Examples of such glaze-forming materials include, but are
not limited to, materials such as magnesium oxide-based material,
boric acid/boric oxide-based material, etc. During firing, the
glaze-forming material/s "bloom" to the surface of the particles
and form a glaze. Alternatively, glazing may be accomplished, for
example, by applying a suitable glaze-forming material onto the
surface of the formed raw material or "green" particles prior to
firing such as by spraying, dipping, and similar methods so that
glazing occurs during particle firing. Further alternatively, a
glaze-forming material may be applied to a fired ceramic particle,
and then fired again in a separate glaze-forming step. In one
embodiment, the glaze forms a relatively hard and relatively
non-porous surface during firing of the particles.
[0165] Advantages of such a glazing treatment include maintaining
the relatively low apparent density of a relatively lightweight
porous particle without the necessity of further alteration, such
as necessity of coating with a separate polymer coating although
optional coatings may be applied if so desired. Furthermore, the
resulting relatively smooth glazed surface of such a particle also
may serve to enhance the ease of multi phase fluid flow, such as
flow of water and gas and oil, through a particulate pack, such as
through a proppant pack in a fracture, resulting in increased
fracture conductivity.
[0166] It will be understood that the characteristics of glazing
materials, penetrating materials and/or coating materials given
herein, such as composition, amounts, types, are exemplary only. In
this regard, such characteristics may be selected with benefit of
this disclosure by those of skill in the art to meet and withstand
anticipated downhole conditions of a given application using
methods known in the art, such as those described herein.
[0167] Examples of suitable porous material particulates that may
be selected for use in aqueous based carrier fluids include, but
are not limited to porous ceramics, porous polymeric materials or
any other porous material or combinations thereof suitable for
selection for combination of internal porosity and permeability to
achieve desired properties, such as strength and/or ASG, for
particular downhole conditions and/or well treatment applications
as described elsewhere herein. For example, porous ceramic
particles may be manufactured by firing at relatively low
temperatures to avoid loss of porosity due to crystallization and
driving off of water. Particular examples include, but are not
limited to, porous ceramic particles available from Carbo Ceramics
Inc. of Irving, Texas composed of fired kaolinitic clay that is
fired at relatively low temperature of about 1235.degree. F. or
about 1300.degree. F. (or about 700.degree. C. and that has trace
amounts of components such as cristobalite, mullite and opalite),
polyolefin particles, and similar components.
[0168] Well Treating Aggregates
[0169] The relatively lightweight particulates may further comprise
a multitude of aggregated components bonded together. Such
aggregates may consist of at least one organic lightweight material
and at least one weight modifying agent. The ASG of the organic
lightweight material is either greater than or less than the ASG of
the well treating aggregate. Such aggregates facilitate improved
placement of the proppant within the fracture while minimizing
settling, thereby enhancing fracture conductivity. The aggregates
are particularly effective in reducing fines generation as a result
of closure stress applied on the proppant pack. In addition, the
aggregates are effective in reducing particulate production.
[0170] The weight modifying agent may be a weighting agent having a
higher ASG than the organic lightweight material. The presence of
the weighting agent renders a well treating aggregate having a ASG
greater than the ASG of the organic lightweight material.
Alternatively, the weight modifying agent may be a weight reducing
agent having a lower ASG than the organic lightweight material. The
presence of the weight reducing agent renders a well treating
aggregate having a ASG less than the ASG of the organic lightweight
material.
[0171] The aggregates are comprised of a continuous phase composed
of the organic lightweight material and a discontinuous phase
composed of a weight modifying material. The volume ratio of resin
(continuous phase) to weight modifying agent (discontinuous phase)
is approximately 75:25. The aggregate particle diameter is
approximately 850 microns. The average diameter of the weight
modifying agent particulates is approximately 50 microns.
[0172] The compressive strength of the aggregate is greater than
the compressive strength of the organic lightweight material. When
hardened, the aggregate exhibits a strength or hardness to prevent
deformation at temperatures and/or formation closure stresses where
substantially deformable materials generally become plastic and
soften.
[0173] In a preferred embodiment, the weight modifying agent is
selected so as to modify or customize the ASG of the aggregate in
order to impart to the aggregate the desired ASG. For example, the
organic lightweight material may be treated with a weight modifying
agent in such a way that the aggregate has a ASG close to the ASG
of the carrier fluid so that it is neutrally buoyant or
semi-buoyant in a fracturing fluid or sand control fluid.
[0174] Alternatively, the weight modifying material may be selected
so that the aggregate has the structural support and strength to
withstand the closure stresses of a hydraulic fractured formation,
or other downhole stresses.
[0175] The amount of weight modifying agent in the well treating
aggregate is such as to impart to the well treating aggregate the
desired ASG. Typically, the amount of weight modifying agent in the
well treating aggregate is between from about 15 to about 85
percent by volume of the well treating aggregate, most preferably
approximately about 52 percent by volume.
[0176] The particle sizes of the weight modifying agent are
preferably between from about 10 to about 200 microns.
[0177] The organic lightweight material is preferably a polymeric
material, such as a thermosetting resin, including polystyrene, a
styrene-divinylbenzene copolymer, a polyacrylate, a
polyalkylacrylate, a polyacrylate ester, a polyalkyl acrylate
ester, a modified starch, a polyepoxide, a polyurethane, a
polyisocyanate, a phenol formaldehyde resin, a furan resin, or a
melamine formaldehyde resin. The ASG of the organic lightweight
material generally less than or equal to 1.1. In a preferred
embodiment, the ASG of the material is between about 0.7 to about
0.8.
[0178] The amount of organic lightweight material in the aggregate
is generally between from about 10 to about 90 percent by volume.
The volume ratio of organic lightweight material:weight modifying
agent in the aggregate is generally between from about 20:80 to
about 85:15, most preferably about 25:75. As an example, using an
organic lightweight material having an ASG of 0.7 and a weight
modifying agent, such as silica, having an ASG of 2.7, a 20:80
volume ratio would render an aggregate ASG of 2.20 and a 85:15
volume ratio would render an ASG of 1.0; a 75:25 volume ratio would
render an ASG of 1.20.
[0179] In a preferred mode, the ASG of the well treating aggregate
is at least about 0.35. In a most preferred mode, the ASG of the
well treating aggregate is at least about 0.70, more preferably
1.0, but not greater than about 2.0.
[0180] The weight modifying agent may be sand, glass, hematite,
silica, sand, fly ash, aluminosilicate, and an alkali metal salt or
trimanganese tetraoxide. In a preferred embodiment, the weight
modifying agent is selected from finely ground sand, glass powder,
glass spheres, glass beads, glass bubbles, ground glass, glass
bubbles, borosilicate glass or fiberglass. Further, the weight
modifying agent may be a cation selected from alkali metal,
alkaline earth metal, ammonium, manganese, and zinc and an anion
selected from a halide, oxide, a carbonate, nitrate, sulfate,
acetate and formate. For instance, the weight modifying agent may
include calcium carbonate, potassium chloride, sodium chloride,
sodium bromide, calcium chloride, barium sulfate, calcium bromide,
zinc bromide, zinc formate, zinc oxide or a mixture thereof.
[0181] Glass bubbles and fly ash are the preferred components for
the weight reducing agent.
[0182] The aggregates are generally prepared by blending the
organic lightweight material with weight modifying agent for a
sufficient time in order to form a slurry or a mud which is then
formed into sized particles. Such particles are then hardened by
curing at temperatures ranging from about room temperature to about
200.degree. C., preferably from about 50 to about 150.degree. C.
until the weight modifying agent hardens around the organic
lightweight material.
[0183] In a preferred mode, the organic lightweight material forms
a continuous phase; the weight modifying forming a discontinuous
phase.
[0184] The ASG of the well treating aggregate is generally less
than or equal to 2.0, preferably less than or equal to 1.5, to meet
the pumping and/or downhole formation conditions of a particular
application, such as hydraulic fracturing treatment, sand control
treatment.
[0185] Further, the aggregates exhibit a Young's modulus of between
about 500 psi and about 2,000,000 psi at formation conditions, more
typically between about 5,000 psi and about 500,000 psi, more
typically between about 5,000 psi and 200,000 psi at formation
conditions, and most typically between about 7,000 and 150,000 psi
at formation conditions. The Young's modulus of the aggregate is
substantially higher than the Young's modulus of the organic
lightweight material or the weighting agent.
[0186] In one embodiment, such a material may be employed as
proppant/sand control particulate material at temperatures up to
about 250.degree. F., and closure stresses up to about 8000 psi.
However, these ranges of temperature and closure stress are
exemplary only, it being understood that the disclosed materials
may be employed as proppant/sand control materials at temperatures
greater than about 250.degree. F. and/or at closure stresses
greater than about 8000 psi.
[0187] In a preferred embodiment the relatively lightweight
proppant or particulates are suspended in a carrier fluid and
introduced into the subterranean formation at a pressure above a
fracturing pressure of the subterranean formation. In this method,
at least a portion of the individual particles of the particulate
material are substantially neutrally buoyant in the carrier
fluid.
[0188] Further, the relatively lightweight and/or substantially
neutrally buoyant proppant or particulate is used in a sand control
method for a wellbore penetrating a subterranean formation and may
be introduced into the wellbore in a slurry with a carrier fluid;
the particulate material being placed adjacent the subterranean
formation to form a fluid-permeable pack that is capable of
reducing or substantially preventing the passage of formation
particles from the subterranean formation into the wellbore while
at the same time allowing passage of formation fluids from the
subterranean formation into the wellbore. In this method at least a
portion of the individual particles of the particulate material may
be substantially neutrally buoyant in the carrier fluid.
[0189] When employed in well treatments, the relatively lightweight
and/or substantially neutrally buoyant particulates may be
introduced into the wellbore at any concentration deemed suitable
or effective for the downhole conditions to be encountered. For
example, a well treatment fluid may include a suspension of
proppant or sand control aggregates. Alternatively, it is possible
that a well treatment fluid may include a suspension that contains
a mixture of any of the above referenced relatively lightweight
and/or substantially neutrally buoyant particulates or a mixture of
any of the above referenced relatively lightweight and/or
substantially neutrally buoyant particulates and conventional
fracture proppant or sand control particulates, such as sand.
[0190] When used in hydraulic fracturing, a suspension of
relatively lightweight and/or substantially neutrally buoyant
particulates in a carrier fluid may be injected into a subterranean
formation in conjunction with a hydraulic fracturing treatment or
other treatment at pressures sufficiently high enough to cause the
formation or enlargement of fractures or to otherwise expose the
aggregates to formation closure stress. Such other treatments may
be near wellbore in nature (affecting near wellbore regions) and
may be directed toward improving wellbore productivity and/or
controlling the production of fracture proppant or formation sand.
Particular examples include gravel packing and frac-packs.
Moreover, such aggregates may be employed alone as a fracture
proppant/sand control particulate, or in mixtures in amounts and
with types of fracture proppant/sand control materials, such as
conventional fracture or sand control particulate.
[0191] In one exemplary embodiment, a gravel pack operation may be
carried out on a wellbore that penetrates a subterranean formation
to prevent or substantially reduce the production of formation
particles into the wellbore from the formation during production of
formation fluids. The subterranean formation may be completed so as
to be in communication with the interior of the wellbore by any
suitable method known in the art, for example by perforations in a
cased wellbore, and/or by an open hole section. A screen assembly
such as is known in the art may be placed or otherwise disposed
within the wellbore so that at least a portion of the screen
assembly is disposed adjacent the subterranean formation. A slurry
including the relatively lightweight and/or substantially neutrally
buoyant particulates and a carrier fluid may then be introduced
into the wellbore and placed adjacent the subterranean formation by
circulation or other suitable method so as to form a
fluid-permeable pack in an annular area between the exterior of the
screen and the interior of the wellbore that is capable of reducing
or substantially preventing the passage of formation particles from
the subterranean formation into the wellbore during production of
fluids from the formation, while at the same time allowing passage
of formation fluids from the subterranean formation through the
screen into the wellbore. It is possible that the slurry may
contain all or only a portion of the relatively lightweight and/or
substantially neutrally buoyant particulates. In the latter case,
the balance of the particulate material of the slurry may be
another material, such as a conventional gravel pack or sand
control particulate.
[0192] As an alternative to use of a screen, the sand control
method may use the relatively lightweight and/or substantially
neutrally buoyant particulates in accordance with any method in
which a pack of particulate material is formed within a wellbore
that it is permeable to fluids produced from a wellbore, such as
oil, gas, or water, but that substantially prevents or reduces
production of formation materials, such as formation sand, from the
formation into the wellbore. Such methods may or may not employ a
gravel pack screen, may be introduced into a wellbore at pressures
below, at or above the fracturing pressure of the formation, such
as frac pack, and/or may be employed in conjunction with resins
such as sand consolidation resins if so desired.
[0193] The relatively lightweight and/or substantially neutrally
buoyant particulate may be formed from materials that are chipped,
ground, crushed, or otherwise processed to produce particulate
material having any particle size or particle shape suitable for
use in the methods disclosed herein. In one exemplary embodiment,
particle sizes include, but are not limited to, sizes ranging from
about 4 mesh to about 200 mesh, alternatively from about 12 mesh to
about 50 mesh. In another exemplary embodiment, particle sizes
include, but are not limited to, sizes ranging from about 8 mesh to
about 40 mesh, alternatively from about 14 mesh to about 40 mesh,
alternatively from about 16 mesh to about 40 mesh, alternatively
from about 20 mesh to about 30 mesh. Shapes of such particles may
vary, but in one embodiment may be utilized in shapes having
maximum length-based aspect ratio values as described elsewhere
herein for particles, and in one embodiment may have a maximum
length-based aspect ratio of less than or equal to about 5. Once
again, the preceding ranges of values are exemplary only, and
values outside these ranges are also possible.
[0194] Particle size of the disclosed particulate materials may be
selected based on factors such as anticipated downhole conditions
and/or on relative strength or hardness of the particulate
material/s selected for use in a given application. In this regard,
larger particle sizes may be more desirable in situations where a
relatively lower strength particulate material is employed. For
example, 12/20 mesh ground walnut hulls may be desirable for use
where closure stresses of up to about 1500 psi are anticipated.
Smaller particle sizes may be more desirable in situations where a
relatively higher strength particulate material is employed. For
example 20/40 mesh ground walnut hulls treated with a modifying
agent described elsewhere herein may be desirable for use where
closure stresses of up to about 3000 psi, alternatively up to about
4000 psi are anticipated.
[0195] Type/s of particulate materials for use as a particulate as
disclosed herein may also be selected based on factors such as
anticipated downhole conditions. In one exemplary embodiment,
walnut hull-based particulates may be desirable for use where
downhole temperatures of up to about 200.degree. F. are
anticipated, and apricot pit-based particulates may be desirable
for use where downhole temperatures of up to about 250.degree. F.,
alternatively of up to about 275.degree. F. are anticipated.
However, it will be understood that walnut hull-based materials may
also be employed at temperatures greater than about 200.degree. F.,
and apricot pit-based materials may be employed at temperatures
greater than about 275.degree. F. In this regard, type/s of
particulate materials may be selected with benefit of this
disclosure for use in a given application by those of skill in the
art to meet requirements of a given application, (e.g., including
to withstand anticipated downhole conditions), for example, using
one or more testing methods such as those disclosed elsewhere
herein. Furthermore, given particulate material/s may be treated
(e.g., exposed to a modifying agent, coated with protective and/or
hardening layers, etc.) so as to render a given particulate
material suitable for the requirements of a given application.
[0196] In another disclosed embodiment, blends of two or more
different types of relatively lightweight particulates having
different characteristics, such as different porosity,
permeability, ASG or setting velocity in the carrier fluid, may be
employed in well treatment. Such blends may be further employed in
any type of well treatment application, including in any of the
well treatment methods described elsewhere herein. In one exemplary
embodiment, such blends may be employed to optimize hydraulic
fracture geometries to achieve enhanced well productivity. Choice
of different materials and amounts thereof to employ in such blends
may be made based on one or more well treatment considerations
including, but not limited to, objective/s of well treatment, such
as for sand control and/or for creation of propped fractures, well
treatment fluid characteristics, such as ASG and/or rheology of
carrier fluid, well and formation conditions such as depth of
formation, formation porosity/permeability, formation closure
stress, type of optimization desired for geometry of
downhole-placed particulates such as optimized fracture pack
propped length, optimized sand control pack height, optimized
fracture pack and/or sand control pack conductivity and
combinations thereof. Such different types of aggregates may be
selected, for example, to achieve a blend of different ASGs
relative to the selected carrier fluid.
[0197] In one exemplary embodiment, selected blends of conventional
sand proppant, relatively lightweight particulates of ground or
crushed nut shells at least partially surrounded by at least one
layer component of protective or hardening coating, and selectively
configured porous materials such as relatively lightweight porous
material fired kaolinitic particles treated with a
penetrating/coating materials described herein may be employed in a
hydraulic fracture treatment utilizing ungelled or weakly gelled
carrier fluid. In such an embodiment, these different types of
particles may be employed in any relative volume or weight amount
or ratio suitable for achieving desired well treatment results.
[0198] In another specific example, these different types of
particles may be employed in a well treatment particulate
composition including about 1/3 by weight of conventional sand
proppant by total weight of well treatment particulate, about 1/3
by weight of relatively lightweight particulate, such as core of
ground or crushed nut shells at least partially surrounded by at
least one layer component of protective or hardening coating) by
total weight of well treatment particulate, and about 1/3 by weight
of selectively configured relatively lightweight porous material,
such as fired kaolinitic particles treated with a
penetrating/coating materials described herein, by total weight of
well treatment particulate. It will be understood that the
foregoing relative amounts are exemplary only and may be varied,
for example, to achieve desired results and/or to meet cost
objectives of a given treatment. It will also be understood that
the disclosed methods and compositions may also be practiced with
such blends using other types of relatively lightweight particulate
materials as described elsewhere herein, such as porous polymeric
materials, such as polyolefins, styrene-divinylbenzene based
materials, polyalkylacrylate esters and modified starches. Further,
any of the disclosed porous materials may be employed in "neat" or
non-altered form in the disclosed blends where apparent density and
other characteristics of the particle are suitable to meet
requirements of the given well treating application.
[0199] A suspension of the relatively lightweight proppant in a
carrier may serve as a storable aqueous pumpable suspension when
the relatively lightweight proppant is substantially neutrally
buoyant. Such suspensions exhibit sufficient suspension stability
for short to moderate term storage. Such suspensions may then be
pumped or placed downhole as is or diluted on the fly. The
relatively lightweight proppant is preferably a ULW proppant.
[0200] The carrier fluid has an ASG substantially equal to the ASG
of the substantially neutrally buoyant particulate. The relatively
lightweight particulate is preferably suspended in either a
weighted carrier fluid or a weakly gelled carrier fluid or a
combination of thereof. The carrier fluid may be weighted by the
addition of a salt, such as sodium chloride, potassium chloride,
etc.
[0201] The ASG of the relatively lightweight particulate is
preferably the same as, but no greater than 0.25 higher than, the
ASG of the carrier fluid; preferably the ASG of the relatively
lightweight particulate is no greater than 0.20 higher than the ASG
of the carrier fluid. For example, LiteProp.TM. 125 lightweight
proppant, a product of BJ Services Company, having an ASG of 1.25
is neutrally buoyant in a 10.4 lb/gal (ppg) brine and is easily
suspended in such brine. As such, the particulate is used to weight
the suspension fluid. A brine lower in ASG than the particulate and
having slight viscosity could be employed.
[0202] When suspended in a weakly gelled carrier fluid, the carrier
fluid may further contain a friction reducing agent, the amount of
friction reducing agent being between from about 0 to about 10
pounds per thousand gallons of carrier fluid. Suitable friction
reducing agents include guar, hydroxypropyl guar, acrylamides
including acrylamide copolymers, aliphatic alcohols, aliphatic
acids, aliphatic amines, aliphatic amides, and alkoxylated
alkanolamides.
[0203] The weakly gelled carrier fluid further is slightly
viscosified by common low cost gelling agent and typically exhibits
a viscosity of from about 1 to about 20 cps, preferably from about
1 to about 10 cps.
[0204] The carrier fluid preferably may further contain a
suspending or thixotropic agent. Suitable suspending/thixotropic
agents include welan gum, xanthan gum, cellulose and cellulosic
derivatives such as hydroxyethyl dellulose (HEC),
carboxymethyl-hydroxyethyl-cellulose, guar and its derivatives,
starch and polysaccharides, succinoglycan, polyalkylene oxides such
as polyethylene oxide, bentonite, attapulgite, mixed metal
hydroxides, clays such as bentonite and attapulgite, mixed metal
hydroxides, oil in water emulsions created with paraffin oil and
stabilized with ethoxylated surfactants, poly (methyl vinyl
ether/maleic anhydride) decadiene copolymer, etc.
[0205] The preferred suspending agent is either carrageenan or
scleroglucan. Carrageenan, a high molecular weight polysaccharide
derived from seaweed, and scleroglucan, a water soluble natural
polymer produced by fermentation of the filamentous fungi
Sclerotium rofsii, provide better stability and minimize the risk
of settling.
[0206] Although any carrageenan suitable for forming gels and/or
otherwise acting as a suspension agent may be employed (including
those carrageenans having a molecular weight greater than about
500,000 and less than about 75,000), typically a carrageenan has a
molecular weight of between about 75,000 and about 500,000. (Unless
otherwise noted, all molecular weights expressed herein refer to
weight average molecular weight.) More typically, the carrageenan
has a molecular weight of between about 150,000 and about 250,000,
and even more typically a carrageenan has a molecular weight of
about 200,000. Specific carrageenan types include kappa, iota and
lambda carrageenans. Typically, iota carrageenan is employed.
Mixtures of carrageenan types are also possible. A specific example
of a suitable iota carrageenan for use in the disclosed method is
"LSS-1" from BJ Services Company. Other suitable carrageenans
include carrageenan gums and are disclosed in U.S. Pat. No.
6,173,778, herein incorporated by reference.
[0207] Some iota carrageenan materials may require heating to above
the solubility temperature to achieve hydration, for example to
about 80.degree. C. In other cases, an iota carrageenan material
may be hydrated without prior heating especially in the presence of
sodium ions. Examples of such iota carrageenan materials include
"cold water soluble" iota carrageenans, which are soluble at
temperatures of about 20.degree. C. without prior heating as long
as sodium is present, such as in the form of sodium hydroxide or
sodium carbonate.
[0208] Further preferred as the suspending agent for use in the
invention are scleroglucans including scleroglucan gums. Suitable
scleroglucan gums include those commercially available as Biovis, a
product of SKW. Specific examples of suspending agents useful for
the purposes of the present invention include such polysaccharides
as welan gums "BIOZAN", Kelco, San Diego, Calif., polyanionic
cellulose "DRISPAC", Drilling Specialties, Bartlesville, Okla.,
succinoglycan "SHELLFLO-S", Shell International Chemical Co., Ltd.,
London, England; polyethylene oxide "POLYOX PEO"; and mixed metal
hydroxides "POLYVIS", SKW, Trostberg, Germany.
[0209] The amount of suspending agent used in the storable slurry
ranges from about 0.025 to about 1.0 weight percent of the
suspension.
[0210] The carrier fluid may further contain a gelling agent,
crosslinking agent, gel breaker, surfactant, biocide, surface
tension reducing agent, foaming agent, defoaming agent,
demulsifier, non-emulsifier, scale inhibitor, gas hydrate
inhibitor, polymer specific enzyme breaker, oxidative breaker,
buffer, clay stabilizer, acid or a mixture thereof and other well
treatment additives known in the art. The addition of such
additives to the carrier fluids minimizes the need for additional
pumps required to add such materials on the fly.
[0211] As set forth in FIG. 3, use of a storable pumpable
suspension offers significant operational, logistical and economic
advantages. First, the slurries may be pre-mixed at a remote site
and transported to location. Alternatively, the slurry could be
mixed on location prior to treatment.
[0212] Further, the use of a relatively lightweight particulate
containing slurry eliminates the need for a slurry blender, as well
as fluid mixing unit, on location since a simple configuration of
metering valves and a pump would allow the neat slurry to be
diluted in-line with water to the desired concentration. As set
forth in FIG. 3, a prototypical set-up may consist of storable
suspension storage unit 80. At least one high pressure pump, shown
as a series of pumps 60A, 60B and 60C, serve to inject the
pre-slurry into wellhead 70. Transfer pump 90, optionally with
proportioning capabilities, may be used to assist in the transport
of the pumpable slurry into the wellhead via high pressure pumps
60A, 60B and 60c. The mixing equipment need only include such
equipment that is capable of (a) mixing the brine (dissolving
soluble salts), and (b) homogeneously dispersing in the
substantially neutrally buoyant particulate material.
[0213] In FIG. 4, water storage unit 100 may contain egress lines
100A and 100B for proportioning with dilution fluid inline to the
stored slurry, thus enabling extremely accurate ramping. The
proportional slurry is then directed to the high pressure pumps for
injection into the well.
[0214] Thus, the use of relatively lightweight and/or substantially
neutrally buoyant particles in accordance with the invention
eliminates the need for a fracturing blender on location; the more
simpler configuration of metering valves and pumps allowing the
pumpable slurry to be diluted in-line to the desired concentration.
A further benefit is the improved control of concentrations of
proppants, especially since liquids are more accurately metered
than solids.
[0215] The elimination of equipment on location has several
economic advantages in that it saves on equipment costs and, in
areas where job location space is at a premium, such as at
mountainside locations, wells that were previously incapable of
being stimulated become realistic targets. Further, the suspension
of the invention provides the opportunity to pump the slurry
concentrate from a transport located some distance from the well
location versus conventional systems which require proppant
transport near the blender and wellhead.
EXAMPLES
[0216] The following examples are illustrative and should not be
construed as limiting the scope of the invention or claims
thereof.
Example 1
[0217] Conductivity tests were performed according to API RP 61
(1.sup.st Revision, Oct. 1, 1989) using an API conductivity cell
with Ohio sandstone wafer side inserts. Each particulate material
sample was loaded into the cell and closure stress applied to the
particulate material using a "DAKE" hydraulic press having a
"ROSEMOUNT" differential transducer (#3051C) and controlled by a
"CAMILE" controller. Also employed in the testing was a
"CONSTAMETRIC 3200" constant rate pump which was used to flow
deionized water through each particulate sample.
[0218] The coated ground walnut particulate material employed was
ground walnut hulls from "COMPOSITION MATERIALS, INC." having a
size of about 12/20 mesh and having an in situ Young's modulus of
from about 1,000,000 psi to about 2,000,000 psi. The ground walnut
particulate material was coated with a layer of BORDEN "SIGMASET
LV" low volatility resin in an amount of about 12% by weight of
total particulate weight, and the particles were manufactured by
"BORDEN CHEMICAL". The coated ground walnut particulate material
was tested alone, with no other particulate material blended in. It
will be understood with benefit of this disclosure that other
particles having a similar modulus described elsewhere herein
(e.g., ground or crushed nut shells, ground or crushed seeds, etc.)
may also be employed in such applications as the sole proppant or
sand control particulate component of a fracturing fluid, frac pack
composition, or sand control blend.
[0219] Experimental parameters for the coated walnut shell
conductivity evaluation are shown in Tables I-III below.
1 TABLE I Fluid Deionized Water Particulate (grams) 63 Top Core
(cm) 0.91 Bot Core (cm) 0.968 Initial Total Width (cm) 5.462 Width
Pack, initial (cm) 1.134
[0220]
2TABLE II Temperature 150 Particulate Size 12/20 Closure Pressure
500-2000 psi Concentration 2 lbs/ft2 Fluid Pressure (psi) 387
Baseline 238 Darcies @1000 psi
[0221]
3TABLE III Test Water Data Rate Closure *Time Temp mls/ Viscosity
DP Width Conductivity Permeability Stress (Hours) .degree. C. min
cp psi inches md-ft darcies psi 0 68.45 7.89 0.41 0.00386 0.433
22,608 626 524 10 65.20 16.27 0.43 0.01195 0.427 15,756 442 456 20
65.19 7.73 0.43 0.00613 0.406 14,585 432 1001 30 65.15 7.80 0.43
0.01445 0.355 6,251 211 2029 40 65.21 7.87 0.43 0.01469 0.351 6,203
212 2019 50 65.21 7.82 0.43 0.01483 0.348 6,106 211 2021 70 65.22
7.79 0.43 0.01516 0.346 5,947 206 2021 *Values given represent an
average of an hour's data at each given point.
[0222] As may be seen from the results of this example, a
relatively lightweight particulate that is substantially neutrally
buoyant in a 10 pound per gallon brine, may advantageously be
employed to yield a proppant pack having relatively good
conductivity. At 1,000 psi closure stress, the pack of relatively
lightweight proppant material exhibited permeabilities equal to or
exceeding any of the conventional proppants (sand, etc.).
Example 2
[0223] Using a procedure similar to that of Example 1, the same
type of 12/20 mesh ground walnut hull core material was tested with
different types of resin layers from BORDEN. Testing was carried
out for all samples at 150.degree. F. and closure stresses ranging
from 500 psi to 2000 psi. For two of samples, testing was also
carried out at 200.degree. F. and closure stress of 2200 psi. Resin
type and amounts used in each sample are identified in Table IV.
Results of this testing is given in Tables V and VI, and in FIGS. 5
and 6.
4TABLE IV BORDEN Resin Layers on 12/20 Mesh Ground Walnut Shell
Material Layer Type and Amount (% by Weight of Total Weight Sample
Identifier of Particle)* A Inner layer of 2% by weight BORDEN "2AC"
with Outer Layer of 4% by weight BORDEN "SIGMASET LV" B Layer of 6%
by weight BORDEN "SIGMASET LV" resin (Coated particles having
Borden identification code "66040") C Layer of 6% by weight BORDEN
"SIGMASET LV" resin (Coated particles having Borden identification
code "66535") D BORDEN Two Coat Resin -- Inner layer of 2% by
weight separate hardener material and outer layer of 3% by weight
"SIGMASET LV" (Coated particles having Borden identification code
"2PN3x") E Layer of 12% by weight BORDEN "SIGMASET LV" *In Table
IV, BORDEN product identification codes 66040 and 66535 denote
particles coated with "SIGMASET # LV" resin having modified curing
characteristics, i.e., the first digit in the code represents the %
by weight of resin applied as a percentage of total particle weight
(e.g., 6%), # the second and third digits in the code represent
weight percentage of the first resin component (e.g., 60% and 65%
respectively), # and the fourth and fifth digits represent weight
percentage of the second resin component (e.g., 40% and 35%
respectively).
[0224]
5TABLE V Permeability, Darcies Closure Stress, psi Sample A Sample
B Sample C Sample D Sample E 500 453 205 383 429 432 1000 303 146
200 153 319 2000 220 46 94 88 206 105 76
[0225]
6TABLE VI Cell Width, Inches Closure Stress, psi Sample A Sample B
Sample C Sample D Sample E 500 0.43 0.43 0.41 0.41 0.43 1000 0.41
0.4 0.38 0.39 0.406 2000 0.36 0.345 0.3 0.35 0.35 2200 0.32
0.299
[0226] FIG. 5 shows the permeability of the relatively lightweight
particulate core materials having the various types of resin layers
of this example at 500, 1000 and 2000 psi closure stresses and
150.degree. F.
[0227] FIG. 6 shows pack or conductivity cell width of the
relatively lightweight particulate core materials having the
various types of resin layers of this example at 500, 1000 and 2000
psi closure stresses and 150.degree. F. Also shown is cell or pack
width of the relatively lightweight particulate materials Samples A
and E at 2200 psi closure stress and 200.degree. F.
[0228] The results of Examples 1 and 2 illustrate just one way that
relatively lightweight particulate core materials may be evaluated
with various types and/or amounts of resins to fit particulate
conditions, for example, anticipated wellbore or formation
conditions. With benefit of this disclosure, those of skill in the
art will understand that using this or other methods known in the
art suitable for simulating anticipated downhole conditions, types
of relatively lightweight material core materials and coatings (or
combinations of two or more coatings) may be selected or tailored
for use in a given desired application.
Example 3
[0229] Using a procedure similar to that of Example 1, conductivity
tests were performed on three different samples of 12/20 mesh
ground walnut shells at 150.degree. F. and at a concentration of 1
lb/ft.sup.2: Sample A (treated with inner layer of phenol
formaldehyde resin and outer layer of urethane epoxy resin); Sample
B (soaked for 4 hours at room temperature in FSA-1 siloxane-based
compound); and Sample C (spray treated with FSA-1 in an amount of
26% by weight of the ground walnut hull material). The particles of
Samples A and C were manufactured by FRITZ, while the particles of
Sample B were manufactured in the laboratory. Results of this
testing is shown in Table VII and FIG. 7.
7TABLE VII Permeability, Darcies Closure Stress, psi Sample A
Sample B Sample C 1000 91 240 250 2000 86 170 120 3000 30 100
80
[0230] FIG. 7 shows the permeability of the ground walnut hull
materials of the three samples of this example at 500, 1000 and
2000 psi closure stresses and 150.degree. F.
[0231] The results of this example illustrate how ground walnut
hull materials modified with silane-based modifying agent may be
used to form particulate packs having good permeability at
increasing closure stresses.
Example 4
[0232] Using a procedure similar to that of Example 1, conductivity
tests were performed on two different samples of 12/20 mesh ground
walnut shells at 150.degree. F. and at a concentration of 2
lb/ft.sup.2: Sample A (treated with urethane resin) and
manufactured by FRITZ; and Sample B (soaked for 4 hours at room
temperature in FSA-1 siloxane-based compound). Results of this
testing is shown in Tables VIII-XI.
8TABLE VIII Sample A: Resin Coated Ground Walnut Hulls Temperature
150 Particulate Size 12/20 Closure Pressure 3000 psi Concentration
2 lbs/ft2 Fluid Pressure (psi) 200
[0233]
9TABLE IX Sample A: Resin Coated Ground Walnut Hulls Test Water
Data Rate Closure *Time Temp mls/ Viscosity DP Width Conductivity
Permeability Stress (Hours) .degree. C. min cp psi inches md-ft
darcies Psi 0 64.47 8.48 0.44 0.00635 0.59 15,637 318 1094 10 65.00
8.81 0.43 0.00909 0.55 11,253 246 1105 20 65.00 8.51 0.43 0.00969
0.55 10,190 222 1083 30 64.99 8.50 0.43 0.01567 0.39 6,302 194 2059
40 65.00 8.43 0.43 0.01669 0.39 5,861 180 2036 50 65.01 8.56 0.43
0.01926 0.39 5,162 159 2711 60 64.99 8.62 0.43 0.02654 0.37 3,772
124 3021 70 64.99 8.52 0.43 0.02861 0.37 3,458 114 2992 *Values
given represent an average of an hour's data at each given
point.
[0234]
10TABLE X Sample B: Ground Walnut Hulls Treated with Modifying
Agent Temperature 150.degree. Particulate Size 12/20 Closure
Pressure 3000 psi Concentration 2 lbs/ft2 Fluid Pressure (psi)
450
[0235]
11TABLE XI Sample B: Ground Walnut Hulls Treated with Modifying
Agent Test Water Data Rate Closure *Time Temp mls/ Viscosity DP
Width Conductivity Permeability Stress (Hours) .degree. C. min cp
psi inches md-ft darcies psi 0 64.46 8.21 0.44 0.00372 0.590 25,829
525 1412 10 65.00 8.20 0.43 0.00722 0.550 13,187 288 1405 20 65.00
8.21 0.43 0.00796 0.550 11,970 261 1413 30 64.99 8.20 0.43 0.02105
0.390 4,524 139 2379 40 65.00 8.20 0.43 0.02352 0.370 4,049 131
2379 50 65.01 9.18 0.43 0.03442 0.360 3,097 103 3039 60 64.98 8.20
0.43 0.04794 0.340 1,987 70 3074 70 65.00 8.20 0.43 0.05317 0.334
1,790 64 3043 *Values given represent an average of an hour's data
at each given point.
[0236] The results of this example also illustrate how ground
walnut hull materials modified with silane-based modifying agent
may be used to form particulate packs having good permeability at
increasing closure stresses.
Example 5
[0237] Using equipment similar to that employed for Example 1,
stress tests were performed on particulate packs formed from four
different particulate packs formed from four respective samples of
12/20 mesh naturally occurring particulate material: Sample A
(ground apricot pits); Sample B (ground walnut hulls having about
2% by weight moisture content); Sample C (ground walnut hulls
having about 5% by weight moisture content); and Sample D (ground
olive pits). The particles of each of Samples A through D were
obtained from FRITZ, and were soaked for 4 hours at room
temperature in FSA-1 siloxane-based compound. Each of the
particulate samples was loaded into a test cell at a concentration
of 1 lbs/ft.sup.2 for testing at 150.degree. F. During the test of
each particulate pack, increasing compressive stress was applied to
the pack and the resulting width of the pack within the cell
measured using a sensitive linear variable differential
transducer.
[0238] Results of this testing is shown in FIG. 8 as a plot of pack
width displacement (i.e. reduction in pack width) in millimeters
versus increasing compressive force. As may be seen in FIG. 8, the
modified ground apricot pits of Sample A exhibited the least pack
width reduction with increasing force, translating into most
retained permeability of the four samples at a given stress level.
The modified ground olive pits of Sample D showed the most pack
width reduction with increasing stress, translating into least
retained permeability of the four samples at a given stress level.
The modified ground walnut hulls of Samples B and C exhibited pack
width reduction values in-between those of Samples A and D at most
stress levels. In this regard, the modified ground walnut hulls of
Sample B (having a moisture content of about 2%) exhibited less
pack width reduction than the modified ground walnut hulls of
Sample C (having a moisture content of about 5%) at a given stress
level, showing that lower moisture levels may translate into
increased strength or hardness for a given naturally occurring
material. For example, in one embodiment of the disclosed
compositions and methods, naturally occurring particulate material
(e.g., ground walnut hull material) having a moisture content of
from about 2% by weight of the material to about 5% by weight of
the material may be employed.
Example 6
[0239] To obtain the data for this example, the following procedure
was followed: Measured mass of 25 ml of sample on a graduate
cylinder. Cylinder was tapped several times on the countertop and
the volume adjusted to an even 25 ml prior to weighing.
Mass/volume=bulk density.
[0240] The data of this example is shown in Table XII:
12TABLE XII Bulk Densities Sand 1.721 CarboLite 1.747 Porous
Ceramic-Neat 1.191 Porous Ceramic-2/2 1.238 Porous Ceramic-6% 1.293
Porous Ceramic-8% P-A 1.224 Porous Ceramic-8% P-B 1.198 Porous
Ceramic-10% P 1.32
[0241] FIG. 9 illustrates comparisons of the bulk densities of
various proppants/sand control materials to samples of a selected
porous ceramic material (from Carbo Ceramics, Inc.).
[0242] In the examples, "Carbolite" is a commercial proppant
available from Carbo Ceramics, Inc. "Neat" is untreated porous
ceramic material from Carbo Ceramics, Inc., "2/2" is porous ceramic
material from Carbo Ceramics, Inc. treated with 2% by weight of
particle epoxy inner coating/penetrating material (epoxy is
reaction product of epichlorohydrin and bis-phenol A) and with 2%
by weight of particle phenol formaldehyde resin outer coating
material, "6%" is porous ceramic material from Carbo Ceramics, Inc.
treated with 6% by weight of particle coating/penetrating material
(epoxy is reaction product of epichlorohydrin and bis-phenol A),
"8% P-A" is porous ceramic material from Carbo Ceramics, Inc.
treated with 8% by weight of particle phenol formaldehyde resin
(Sample A), "8% P-B" is porous ceramic material from Carbo
Ceramics, Inc. treated with 8% by weight of particle phenol
formaldehyde resin (Sample B), and "10% P" is porous ceramic
material from Carbo Ceramics, Inc. treated with 10% by weight of
particle phenol formaldehyde resin.
[0243] Data is presented for both the untreated porous material
particle, and for the porous material particle treated with various
types and concentrations of selected penetrating materials. As may
be seen, the bulk apparent density of the resulting particles
varies with varying degree of infiltration or penetration of the
penetrating material into the porous ceramic particle. The samples
designated as 2/2 and 8% P-B may be characterized from SEM thin
section analysis as having limited penetration towards the core of
the particle, apparent effective encapsulation of the air in the
particle core porosity, yet substantial enhancement of the particle
strength as illustrated by the conductivity tests.
[0244] FIGS. 10 and 11 illustrate the permeability versus closure
stress for coated and uncoated ceramic ULW particulates. As shown,
resin coating and impregnation of the ULW particle imparts
significant strength across the closure range and in particular,
enhances the low to mid-range performance of the material. The data
represents equal pack widths for all of the proppants with
adjustments made for each respective density. Both the coated and
uncoated ceramics ULW were tested at 1.4 pounds per square foot
(33.2 kg/m.sup.2). Each of these tests had nearly identical width
measurements for ease of comparison.
Example 7
[0245] The porous particulate material employed was from "Carbo
Ceramics" having a size of about 20/40 mesh. The particulate
material was treated with various penetrating/coating materials
corresponding to the same epoxy or phenol formaldehyde materials
used above. The treated particulate material was tested alone, with
no other particulate material blended in. Comparison materials
include Jordan Sand, "Econoprop" proppant from Carbo Ceramics,
"Econoflex" (coated Econoprop proppant), Hickory sand (Brady Sand),
"PR6000" 2% coated Ottawa sand from BORDEN, and "Carbolite"
proppant from Carbo Ceramics.
[0246] Conductivity tests were performed according to API RP 61
(1.sup.st Revision, Oct. 1, 1989) using an API conductivity cell
with Ohio sandstone wafer side inserts. Each particulate material
sample was loaded into the cell and closure stress applied to the
particulate material using a "DAKE" hydraulic press having a
"ROSEMOUNT" differential transducer (#3051C) and controlled by a
"CAMILE" controller. Also employed in the testing was a
"CONSTAMETRIC 3200" constant rate pump which was used to flow
deionized water through each particulate sample.
[0247] Table XIII shows the proppant pack Permeability and
Conductivity data generated for this example.
13TABLE XIII Porous Ceramic Worksheet PC PC- 4% PC- 6% PC- 8% PC-
2% PC- 6% PC- 8% PC 10% 20/40 20/40 20/40 20/40 20/40 20/40 neat
Epoxy epoxy epoxy &2% resin resin resin Jordan Econoprop
Econoflex Hickory PR 6000 Carbolite Bulk 1.198 1.292 1.34 1.238
1.293 1.224 1.32 1.6 1.6 1.5 1.6 1.54 1.6 Dens Acid 5.7% 1.20%
1.90% 0.30% 0.50% 0.30% 1.70% Solu- bility Po- 50.2% 46.9% 51.8%
54.1% rosity Crush 2000 3.65 .1 0.4 0.1 3000 .3 1.8 0.2 4000 7.52
4.54 1.6 0.1 9.8 0.4 5000 2.6 13.6 0.7 6000 16.88 16.36 0.1 1.9
7000 21.00 7500 4.7 3.1 1.5 8000 20.87 0.2 4.5 10000 13.3 0.5 10.7
12.1 Perme- PC PC 4% PC- 6% PC- 8% PC- 2% PC- 6% PC- 8% PC 10%
20/40 20/40 20/40 20/40 20/40 20/40 ability neat Epoxy epoxy epoxy
&2% resin resin resin Jordan Econoprop Econoflex Hickory PR
6000 Carbolite 2000 149 425 322 409 406 559 1193 508 228 342 287
224 275 500 3000 110 331 226 304 318 376 994 384 170 319 274 144
241 466 4000 70 237 130 190 230 192 786 260 113 295 262 64 208 433
5000 97 110 131 185 151 671 181 80 257 255 42 168 376 6000 64 89
142 110 546 101 47 220 248 21 127 319 7000 48 55 78 361 32 178 225
12 94 252 8000 28 44 46 175 18 135 202 4 61 186 Con- PC- PC- duc-
#1 PC- 4% PC- 6% PC- 8% PC- 2% PC- 6% PC- 8% 10% 20/40 20/40 20/40
20/40 20/40 20/40 tivity neat Epoxy epoxy epoxy &2% resin resin
resin Jordan Econoprop Econoflex Hickory PR 6000 Carbolite 2000
2726 8436 4693 5965 5484 4658 13522 5760 2116 3423 2586 2020 2550
4755 3000 1915 5152 3194 4283 4053 3177 10275 4116 1564 3132 2382
1276 2201 4383 4000 1103 1868 1695 2600 2621 1695 7028 2472 1013
2842 2178 532 1852 4011 5000 949 1356 1616 1983 1221 5406 1729 709
2442 2036 344 1468 3445 6000 747 1042 1345 747 3783 986 405 2042
1895 157 1085 2879 7000 526 604 522 2455 279 1621 1650 94 790 2255
8000 296 463 296 1127 154 1201 1405 31 495 1637
[0248] Data is presented graphically in FIGS. 10-14.
[0249] Conductivity is a function of the width times the
permeability. Advantageously, as disclosed herein in one
embodiment, a selected porous material particulate may be treated
with a selected coating and/or penetrating material to produce a
relatively lightweight particulate sample that at the same lb/sq ft
loading as a conventional sand will occupy a greater width. Even if
the pack permeability is the same, the conductivity, and thus the
proppant pack productability will be higher. Thus, as represented
by the conductivity data, the benefit of the combination of
increased width and the improved permeability may be achieved.
Further, as disclosed herein in one embodiment, a selected porous
material particulate may be treated with a selected coating and/or
penetrating material so that particle strength is maintained to as
high a confining (or closure) stress as possible, which is
reflected more directly by the permeability data. Thus a certain
amount of fracture conductivity at a given stress/temp condition
may be maintained without increasing the cost, and/or by offsetting
any cost increase with improved value. Even in the event of
increased particulate material cost, substantially less particulate
material may be employed to achieve a substantially equivalent
conductivity due to the lesser mass/unit volume.
Example 8
[0250] Using the selected treated material of Examples 6-7,
particles may be produced that are capable for use, such as having
sufficient crush resistance for use or do not crush, under
conditions of 2000 psi closure stress or greater, alternatively
2500 psi closure stress or greater, alternatively 3000 psi closure
stress or greater, alternatively up to at least about 6000 psi
closure stress, alternatively up to at least about 7000 psi closure
stress, and alternatively at least about 8000 psi closure stress,
i.e., almost as resistant to crush as commercial ceramic proppants
which are heavier (e.g., commercial ceramic proppant (CarboLite) is
about 40% heavier). In another embodiment, particles may be
produced that are capable for use (e.g., have sufficient crush
resistance for use or do not crush) under conditions of from about
2000 psi closure stress to about 8000 psi closure stress,
alternatively from about 2500 psi closure stress to about 8000 psi
closure stress, alternatively from about 3000 psi closure stress to
about 8000 psi closure stress. However, it will be understood that
particles may produced that are capable of use at higher closure
stresses than 8000 psi and lower closure stresses than about 2000
psi as well.
[0251] FIGS. 16-23 are cross-sectional and surface SEM photographs
of various treated and untreated samples of porous ceramic
materials from CARBO CERAMICS. Where indicated as "epoxy" or as
"resin", the particular coating/penetrating material is either the
same epoxy or phenol formaldehyde resin employed and identified in
Example 1.
[0252] FIG. 16 shows particles treated with about 10% by weight of
particle resin. FIG. 17 shows particles treated first with 2% by
weight epoxy and second with 2% by weight resin. FIG. 18 shows
untreated particles. FIG. 19 shows particles treated first with 2%
by weight epoxy and second with 2% by weight resin. FIG. 20 shows
surface of untreated particle. FIG. 21 shows untreated particles.
FIG. 22 shows particles treated with 8% by weight epoxy. FIG. 23
shows particles treated with 6% by weight epoxy.
Example 9
[0253] A storable pumpable suspension containing LiteProp 125
neutrally buoyant in a 11.2 ppg sodium bromide brine and containing
15 pounds per thousand gallons of
carboxymethylhydroxyethylcellulose (CMHEC) was prepared by adding
to 11.2 pounds of sodium bromide brine (prepared by adding 163.8
pounds of sodium bromide to 36.8 gallons of water), 0.63 lbs of
CMHEC and stirring at room temperature. To the resulting mixture
was added 630 pounds of LiteProp 125. The mixture was stirred at
room temperature to obtain the pumpable slurry.
Example 10
[0254] A storable pumpable suspension containing LiteProp 175
neutrally buoyant in a 15.5 ppg calcium bromide/zinc bromide brine
and containing 40 pounds per thousand gallons of CMHEC was
prepared. A 15.5 ppg zinc bromide/calcium bromide brine solution
was prepared by adding 26 weight percent of a 19.2 lb calcium
bromide/zinc bromide mixture to 74 weight percent fresh water and
stirring. To 260 gallons of the resulting brine solution was added
740 gallons of water, 40 lbs of CMHEC and 10,000 pounds of LiteProp
175 and stirring at room temperature. The mixture was stirred at
room temperature to obtain the pumpable slurry.
[0255] While the invention may be adaptable to various
modifications and alternative forms, specific embodiments have been
shown by way of example and described herein. However, it should be
understood that the invention is not intended to be limited to the
particular forms disclosed. Rather, the invention is to cover all
modifications, equivalents, and alternatives falling within the
spirit and scope of the invention as defined by the appended
claims.
* * * * *