U.S. patent application number 10/915024 was filed with the patent office on 2006-02-16 for methods and compositions for carrier fluids comprising water-absorbent fibers.
Invention is credited to Philip D. Nguyen.
Application Number | 20060032633 10/915024 |
Document ID | / |
Family ID | 35798895 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060032633 |
Kind Code |
A1 |
Nguyen; Philip D. |
February 16, 2006 |
Methods and compositions for carrier fluids comprising
water-absorbent fibers
Abstract
The present invention relates to methods and compositions for
carrier fluids comprising water-absorbent fibers. One embodiment of
the present invention provides a method of treating a portion of a
subterranean formation, comprising providing a slurry wherein the
slurry comprises a servicing fluid, particulates, and a degradable,
water-absorbent material wherein the degradable, water-absorbent
material acts to help keep the particulates from settling out of
the slurry; and, introducing the slurry into the portion of the
subterranean formation. Another embodiment of the present invention
provides a slurry suitable for use in subterranean operations
comprising a servicing fluid, particulates, and a degradable,
water-absorbent material wherein the degradable, water-absorbent
material acts to help keep the particulates from settling out of
the slurry.
Inventors: |
Nguyen; Philip D.; (Duncan,
OK) |
Correspondence
Address: |
Robert A. Kent;Halliburton Energy Services
2600 S. 2nd Street
Duncan
OK
73536-0440
US
|
Family ID: |
35798895 |
Appl. No.: |
10/915024 |
Filed: |
August 10, 2004 |
Current U.S.
Class: |
166/280.2 ;
507/924 |
Current CPC
Class: |
C09K 8/68 20130101 |
Class at
Publication: |
166/280.2 ;
507/924 |
International
Class: |
E21B 43/12 20060101
E21B043/12 |
Claims
1. A method of treating a portion of a subterranean formation,
comprising: providing a slurry wherein the slurry comprises a
servicing fluid, particulates, and a degradable, water-absorbent
material wherein the degradable, water-absorbent material acts to
help keep the particulates from settling out of the slurry; and,
introducing the slurry into the portion of the subterranean
formation.
2. The method of claim 1 wherein the degradable, water-absorbent
material comprises fibers.
3. The method of claim 2 wherein the degradable, water-absorbent
material has a length of from about 50 microns to 50,000
microns.
4. The method of claim 1 wherein the degradable, water-absorbent
material comprises a poly(lactic acid), a poly(ortho ester),
polybutylene succinate, polybutylene succinate-co-adipate,
polyhydroxybutyrate-valerate, polyhydroxybutyrate-covalerate,
polycaprolactone, a polyester amide, a starch-based polymer, a
polyethylene terephthalate-based polymer, sulfonated polyethylene
terephthalate, polyethylene oxide, polyethylene, polypropylene,
polyvinyl alcohol, an aliphatic aromatic copolyester, or a
combination thereof.
5. The method of claim 1 wherein the slurry comprises degradable,
water-absorbent material present in an amount of from about 0.01%
to about 10% by weight of the slurry.
6. The method of claim 1 wherein the slurry comprises degradable,
water-absorbent material present in an amount of from about 0.1% to
about 2% by weight of the slurry.
7. The method of claim 1 wherein the slurry further comprises a
super-absorbent material.
8. The method of claim 7 wherein the super-absorbent material
comprises modified cellulose, modified lignocellulose, modified
polysaccharide, or a mixture of poly(vinylamine) polymer and
polyacrylic acid.
9. The method of claim 7 wherein the super-absorbent material
comprises an alkali metal salt of polyacrylic acid; a
polyacrylamide; a polyvinyl alcohol; an ethylene maleic anhydride
copolymer; a polyvinyl ether; a hydroxypropylcellulose; a polyvinyl
morpholinone; a polymer or copolymer of vinyl sulfonic acid, a
polyacrylate, a polyacrylamide, a polyvinyl pyridine; a hydrolyzed
acrylonitrile grafted starch, an acrylic acid grafted starch, an
isobutylene maleic anhydride copolymer; a polyphosphazene; or a
combination thereof.
10. The method of claim 1 wherein the particulates are at least
partially coated with a curable resin.
11. The method of claim 1 wherein the particulates are at least
partially coated with a tackifying agent.
12. A method of placing proppant into a fracture within a portion
of a subterranean formation, comprising: providing a slurry wherein
the slurry comprises a servicing fluid, particulates, and a
degradable, water-absorbent material wherein the degradable,
water-absorbent material acts to help keep the particulates from
settling out of the slurry; and, introducing the slurry into the
fracture within a portion of a subterranean formation.
13. The method of claim 12 wherein the degradable, water-absorbent
material comprises fibers.
14. The method of claim 13 wherein the degradable, water-absorbent
material has a length of from about 50 microns to 50,000
microns.
15. The method of claim 12 wherein the degradable, water-absorbent
material comprises a poly(lactic acid), a poly(ortho ester),
polybutylene succinate, polybutylene succinate-co-adipate,
polyhydroxybutyrate-valerate, polyhydroxybutyrate-covalerate,
polycaprolactone, a polyester amide, a starch-based polymer, a
polyethylene terephthalate-based polymer, sulfonated polyethylene
terephthalate, polyethylene oxide, polyethylene, polypropylene,
polyvinyl alcohol, an aliphatic aromatic copolyester, or a
combination thereof.
16. The method of claim 12 wherein the slurry comprises degradable,
water-absorbent material present in an amount of from about 0.01%
to about 10% by weight of the slurry.
17. The method of claim 12 wherein the slurry comprises degradable,
water-absorbent material present in an amount of from about 0.1% to
about 2% by weight of the slurry.
18. The method of claim 12 wherein the slurry further comprises a
super-absorbent material.
19. The method of claim 18 wherein the super-absorbent material
comprises modified cellulose, modified lignocellulose, modified
polysaccharide, or a mixture of poly(vinylamine) polymer and
polyacrylic acid.
20. The method of claim 18 wherein the super-absorbent material
comprises an alkali metal salt of polyacrylic acid; a
polyacrylamide; a polyvinyl alcohol; an ethylene maleic anhydride
copolymer; a polyvinyl ether; a hydroxypropylcellulose; a polyvinyl
morpholinone; a polymer or copolymer of vinyl sulfonic acid, a
polyacrylate, a polyacrylamide, a polyvinyl pyridine; a hydrolyzed
acrylonitrile grafted starch, an acrylic acid grafted starch, an
isobutylene maleic anhydride copolymer; a polyphosphazene; or a
combination thereof.
21. The method of claim 12 wherein the particulates are at least
partially coated with a curable resin.
22. The method of claim 12 wherein the particulates are at least
partially coated with a tackifying agent.
23. A slurry suitable for use in subterranean operations comprising
a servicing fluid, particulates, and a degradable, water-absorbent
material wherein the degradable, water-absorbent material acts to
help keep the particulates from settling out of the slurry.
24. The slurry of claim 23 wherein the degradable, water-absorbent
material comprises fibers.
25. The slurry of claim 24 wherein the degradable, water-absorbent
material has a length of from about 50 microns to 50,000
microns.
26. The slurry of claim 23 wherein the degradable, water-absorbent
material comprises a poly(lactic acid), a poly(ortho ester),
polybutylene succinate, polybutylene succinate-co-adipate,
polyhydroxybutyrate-valerate, polyhydroxybutyrate-covalerate,
polycaprolactone, a polyester amide, a starch-based polymer, a
polyethylene terephthalate-based polymer, sulfonated polyethylene
terephthalate, polyethylene oxide, polyethylene, polypropylene,
polyvinyl alcohol, an aliphatic aromatic copolyester, or a
combination thereof.
27. The slurry of claim 23 wherein the slurry comprises degradable,
water-absorbent material present in an amount of from about 0.01%
to about 10% by weight of the slurry.
28. The slurry of claim 23 wherein the slurry comprises degradable,
water-absorbent material present in an amount of from about 0.1% to
about 2% by weight of the slurry.
29. The slurry of claim 23 wherein the slurry further comprises a
super-absorbent material.
30. The slurry of claim 29 wherein the super-absorbent material
comprises modified cellulose, modified lignocellulose, modified
polysaccharide, or a mixture of poly(vinylamine) polymer and
polyacrylic acid.
31. The slurry of claim 29 wherein the super-absorbent material
comprises an alkali metal salt of polyacrylic acid; a
polyacrylamide; a polyvinyl alcohol; an ethylene maleic anhydride
copolymer; a polyvinyl ether; a hydroxypropylcellulose; a polyvinyl
morpholinone; a polymer or copolymer of vinyl sulfonic acid, a
polyacrylate, a polyacrylamide, a polyvinyl pyridine; a hydrolyzed
acrylonitrile grafted starch, an acrylic acid grafted starch, an
isobutylene maleic anhydride copolymer; a polyphosphazene; or a
combination thereof.
32. The slurry of claim 23 wherein the particulates are at least
partially coated with a curable resin.
33. The slurry of claim 23 wherein the particulates are at least
partially coated with a tackifying agent.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to hydraulic fracturing
treatments. More particularly, the present invention relates to
methods and compositions for carrier fluids comprising
water-absorbent fibers.
[0002] Servicing fluids comprising suspended or slurried
particulates are used in a variety of operations and treatments
performed in oil and gas wells. Such operations and treatments
include, but are not limited to, well completion operations such as
fracturing, gravel packing, and frac-packing.
[0003] An example of a production stimulation operation using a
servicing fluid having particles suspended therein is hydraulic
fracturing. That is, a type of servicing fluid referred to in the
art as a fracturing fluid is pumped through a well bore into a
subterranean zone to be stimulated at a rate and pressure such that
fractures are formed and extended into the subterranean zone. The
fracture or fractures may be horizontal or vertical, with the
latter usually predominating, and with the tendency toward vertical
fractures generally increasing with the depth of the formation
being fractured. Generally, fracturing fluids are viscous fluids in
the form of gels, emulsions, or foams. The particulate materials
used in these operations are often referred to as proppant. The
proppant is deposited in the fracture and functions, inter alia, to
maintain the integrity of the fracture open while maintaining
conductive channels through which such produced fluids can flow
upon completion of the fracturing treatment and release of the
attendant hydraulic pressure.
[0004] Suspended or slurried particulates also are used in well
completion operations such as gravel packing. Gravel packing
treatments are used, inter alia, to reduce the migration of
unconsolidated formation particulates into the well bore. In gravel
packing operations, particulates, often referred to in the art as
gravel, are carried to a well bore in a subterranean producing zone
by a servicing fluid that acts as a gravel carrier fluid. That is,
the particulates are suspended in a carrier fluid, which may be and
usually is viscosified, and the carrier fluid is pumped into a well
bore in which the gravel pack is to be placed. As the particulates
are placed in or near the zone, the carrier fluid leaks off into
the subterranean zone and/or is returned to the surface. The
resultant gravel pack acts as a sort of filter to prevent the
production of the formation solids with the produced fluids.
Traditional gravel pack operations involve placing a gravel pack
screen in the well bore before packing the surrounding annulus
between the screen and the well bore with gravel. The gravel pack
screen is generally a filter assembly used to support and retain
the gravel placed during the gravel pack operation. A wide range of
sizes and screen configurations is available to suit the
characteristics of a well bore, the production fluid, and any
particulates in the subterranean formation. Gravel packs are used,
among other reasons, to stabilize the formation while causing
minimal impairment to well productivity.
[0005] In some situations, hydraulic fracturing and gravel packing
operations may be combined into a single treatment. Such treatments
are often referred to as "frac pack" operations. In some cases, the
treatments are completed with a gravel pack screen assembly in
place with the hydraulic fracturing treatment being pumped through
the annular space between the casing and screen. In this situation,
the hydraulic fracturing treatment ends in a screen-out condition,
creating an annular gravel pack between the screen and casing. In
other cases, the fracturing treatment may be performed prior to
installing the screen and placing a gravel pack.
[0006] Previously, fibrous, non-degradable materials, such as
glass, aramide, nylon, ceramic, and metal, have been added to
carrier fluids to help decrease, or eliminate, the flowback of
proppant both during and after the fracturing treatment. In
addition to decreasing proppant flowback, these fluids also offered
the additional benefits of decreasing the required polymer loadings
of viscosifier and lowering the amount of fluid loss during the
fracturing treatment. Unfortunately, many of these fluids exhibit
limited usefulness, due ate least in part to the fact that after
the placement of proppant inside the fracture, the fibers remain
within the proppant pack, plugging the pore spaces between the
proppant particulate, and causing the fracture conductivity to be
significantly diminished under closure stresses.
[0007] One area where degradable fibers are commonly used is in the
field of disposable absorbent products. Water-absorbent degradable
fibers have been used in a variety of applications, including
disposable diapers, feminine hygiene products, surgical drapes, and
wound dressings. These materials retain their integrity and
strength during use, but after such use, may be disposed of more
efficiently. Such products typically use woven fibers, and, to
date, have not been subjected to widespread use in the oilfield
industry.
SUMMARY OF THE INVENTION
[0008] The present invention relates to hydraulic fracturing
treatments. More particularly, the present invention relates to
methods and compositions for carrier fluids comprising
water-absorbent fibers.
[0009] One embodiment of the present invention provides a method of
treating a portion of a subterranean formation, comprising
providing a slurry wherein the slurry comprises a servicing fluid,
particulates, and a degradable, water-absorbent material wherein
the degradable, water-absorbent material acts to help keep the
particulates from settling out of the slurry; and, introducing the
slurry into the portion of the subterranean formation.
[0010] Another embodiment of the present invention provides a
method of placing proppant into a fracture within a portion of a
subterranean formation, comprising providing a slurry wherein the
slurry comprises a servicing fluid, particulates, and a degradable,
water-absorbent material wherein the degradable, water-absorbent
material acts to help keep the particulates from settling out of
the slurry; and, introducing the slurry into the fracture within a
portion of a subterranean formation.
[0011] Another embodiment of the present invention provides a
slurry suitable for use in subterranean operations comprising a
servicing fluid, particulates, and a degradable, water-absorbent
material wherein the degradable, water-absorbent material acts to
help keep the particulates from settling out of the slurry.
[0012] The features and advantages of the present invention will be
readily apparent to those skilled in the art upon a reading of the
description of the preferred embodiments that follows.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0013] The present invention relates to hydraulic fracturing
treatments. More particularly, the present invention relates to
methods and compositions for carrier fluids comprising
water-absorbent fibers.
[0014] In accordance with the present invention, a carrier fluid
comprising degradable, water-absorbent material (preferably in the
form of fibers) may be used to effectively transport particulates
down hole. The use of degradable, water-absorbent material to
increase a fluid's ability to transport proppant in place of or in
addition to conventional gelling agents (such as guars) may allow
the fluid to carry the particulates with less sensitivity to well
conditions (e.g., permeability, fluid loss, temperature). After the
transport and placement of the particulates in a fracture or a well
bore, the water-absorbent fibers are allowed to degrade. In some
embodiments, the degradation of the water-absorbent fibers occurs
relatively quickly such that the degradation products are returned
to the surface when the carrier fluid reverts to a thin fluid. In
other embodiments, the degradation of the water-absorbent fibers
occurs more slowly and may continue during the production of the
well.
[0015] The addition of degradable, water-absorbent fibers to a
carrier fluid offers numerous benefits. The addition of fibrous
material to a carrier fluid has been proven to decrease the need of
polymer loadings of viscosifier and to decrease fluid loss during
subterranean operations such as fracturing. The degradable,
water-absorbent fibers also act to increase the ability of a
carrier fluid to suspend particles (such a proppant or gravel) by,
inter alia, creating a chemical and/or a crosslinked network or
providing a mechanical network. Such networks may also act to
lessen the effects temperature may have on the viscosity of a
carrier fluid comprising degradable, water-absorbent fibers. This
allows for enhanced carrier fluid performance at moderate or high
temperatures. Particular embodiments of the present invention also
help enhance the clean-up and/or removal of the carrier fluid from
a proppant pack that has been deposited in a subterranean
fracture.
[0016] Moreover, where the chosen degradable, water-absorbent
fibers of the present invention is a hydrolysable ester or another
material that degrades to produce an acid, the degradation of the
fibers may facilitate the breakdown of polymerized guar-based
gelled fluids that may be used in accordance with the present
invention by lowering the pH of the fluids. In particular
embodiments, this lower pH may cause the fluids to de-crosslink,
reducing their viscosity.
[0017] Generally, any know subterranean servicing fluid (such as
those commonly used in fracturing and gravel packing operations)
may be used as a carrier fluid in accordance with the teachings of
the present invention, including aqueous gels, emulsions, and
foams. Suitable aqueous gels are generally comprised of water and
one or more gelling agents. Suitable emulsions can be comprised of
two immiscible liquids such as an aqueous gelled liquid and a
liquefied, normally gaseous, fluid, such as carbon dioxide or
nitrogen. In exemplary embodiments of the present invention, the
servicing fluids are aqueous gels comprised of water, a gelling
agent for gelling the water and increasing its viscosity, and,
optionally, a crosslinking agent for crosslinking the gel and
further increasing the viscosity of the fluid. The increased
viscosity of the gelled, or gelled and cross-linked, servicing
fluid, inter alia, reduces fluid loss and allows the servicing
fluid to transport significant quantities of suspended
particulates. The water used to form the servicing fluid may be
salt water, brine, or any other aqueous liquid that does not
adversely react with the other components.
[0018] A variety of gelling agents may be used, including
hydratable polymers that contain one or more functional groups such
as hydroxyl, carboxyl, sulfate, sulfonate, amino, or amide groups.
Particularly useful are polysaccharides and derivatives thereof
that contain one or more of the monosaccharide units galactose,
mannose, glucoside, glucose, xylose, arabinose, fructose,
glucuronic acid, or pyranosyl sulfate. Examples of natural
hydratable polymers containing the foregoing functional groups and
units that are particularly useful in accordance with the present
invention include guar gum and derivatives thereof, such as
hydroxypropyl guar, and cellulose derivatives, such as hydroxyethyl
cellulose. Hydratable synthetic polymers and copolymers that
contain the above-mentioned functional groups can also be used.
Examples of such synthetic polymers include, but are not limited
to, polyacrylate, polymethacrylate, polyacrylamide, polyvinyl
alcohol, and polyvinylpyrrolidone. The gelling agent used is
generally combined with the water in the fracturing fluid in an
amount in the range of from about 0.01% to about 2% by weight of
the water.
[0019] Examples of crosslinking agents that can be used to further
increase the viscosity of a gelled servicing fluid are alkali metal
borates, borax, boric acid, and compounds that are capable of
releasing multivalent metal ions in aqueous solutions. Examples of
multivalent metal ions include chromium, zirconium, antimony,
titanium, iron, zinc, or aluminum. When used, the crosslinking
agent is generally added to the gelled water in an amount in the
range of from about 0.01% to about 5% by weight of the water.
[0020] The gelled or gelled and cross-linked servicing fluids may
also include internal delayed gel breakers such as enzyme,
oxidizing, acid buffer, or temperature-activated gel breakers. The
gel breakers cause the viscous carrier fluids to revert to thin
fluids that can be produced back to the surface after they have
been used to place particulates in subterranean operations. The gel
breaker used is typically present in the servicing fluid in an
amount in the range of from about 1% to about 5% by weight of the
gelling agent. The servicing fluids may also include one or more of
a variety of well-known additives, such as gel stabilizers, fluid
loss control additives, clay stabilizers, bactericides, and the
like.
[0021] Generally, degradable, water-absorbent materials suitable
for use in the present invention readily absorb water when exposed
to an aqueous environment and slowly degrade or dissolve depending
on the ambient temperature. Examples of degradable, water-absorbent
materials suitable for use with the present invention include
poly(lactic acid) polymers, which may be prepared by the
polymerization of lactic acid and/or lactide. By modifying the
stereochemistry of the poly(lactic acid) polymer, the physical
properties of the polymer, such as melting temperature, melt
rheology, crystallinity, and degree of absorbance, may be modified
as well. Other degradable, water-absorbent materials suitable for
use in the present invention include, but are not limited to,
poly(ortho esters), polybutylene succinate, polybutylene
succinate-co-adipate, polyhydroxybutyrate-valerate,
polyhydroxybutyrate-covalerate, polycaprolactone, polyester amide,
starch-based polymers, and mixtures and co-polymers thereof. Other
suitable polymers include, but are not limited to, polyethylene
terephthalate-based polymers, sulfonated polyethylene
terephthalate, polyethylene oxide, polyethylene, polypropylene,
polyvinyl alcohol, and aliphatic aromatic copolyester. Additional
information on degradable, water-absorbent fibers suitable for use
in increasing a fluid's ability to transport particulates may be
found in U.S. Pat. No. 5,698,322 issued to Tsai, et al., and U.S.
Pat. No. 6,135,987 issued to Tsai, et al., the relevant disclosures
of which are herein incorporated by reference.
[0022] Typically, the water-absorbent materials are present in an
amount of from about 0.01% to about 10% by weight of the carrier
fluid. In particular embodiments, the water-absorbent materials may
be present in an amount of from about 0.1% to about 2% by weight of
the carrier fluid. Any suitable method mixing the water-absorbent
materials with the carrier fluid may be used in accordance with the
teachings of the present invention. In particular embodiments,
these may include batch blending or adding the water-absorbent
materials directly to the flow stream as the carrier fluid is being
pumped down hole (i.e., on-the-fly).
[0023] In some embodiments of the present invention, the
degradable, water-absorbent particulate material is used in the
form of fibers (i.e., materials having a length-to-diameter ratio
greater than about 10). Generally, the degradable, water-absorbent
materials may range in length from about 50 microns to about 50,000
microns, provided the selected length of the fibers does not
interfere with the mixing and pumping of the carrier fluid. In
particular embodiments of the present invention, the
water-absorbent materials may be the only material used to increase
a fluid's ability to carry particulates. In other embodiments, the
water-absorbent materials may be combined and mixed with
viscosifiers (such as guar gums, or viscoelastic surfactants) to
increase the ability of a fluid to transport particulates.
[0024] Particular embodiments of the present invention also further
comprise super-absorbent fibers that may be combined with the
aforementioned degradable, water-absorbent fibers of the present
invention. Preferably, these super-absorbent fibers are
water-swellable, delayed-degradable polymers having a high liquid
absorption capacity. In exemplary embodiments, these
super-absorbent fibers include fibers prepared from a mixture of
poly(vinylamine) polymer and polyacrylic acid. Other examples of
suitable super-absorbent fibers include, but are not limited to,
modified cellulose, modified lignocellulose, and modified
polysaccharide. In particular embodiments, these "modified"
polymers are modified by sulfating the polymers. Furthermore, in
particular embodiments of the present invention, the modified
polymers may be crosslinkable.
[0025] Generally, super-absorbent fibers are made by applying a
super-absorbent polymer to a fiber substrate fibers by surrounding
fibers in the substrate or by bonding the super-absorbent polymer
to itself or to substrate fibers with, for example, crosslinkers in
a super-absorbent polymer or pre-polymer solution. Crosslinking
may, for example, form bonds which range from highly ionic to
highly covalent types of bonds or the like. These bonds can be
further augmented with hydrogen bonds and/or induced polar bonds.
Suitable methods of applying the super-absorbent polymer to the
fiber substrate include saturation, printing, coating, and
spraying. Examples of suitable application methods are taught in
U.S. Pat. No. 4,500,315 issued Feb. 19, 1985, PCT Publication No.
WO 00/50096 published Aug. 31, 2000, European Patent Application
No. 0 947 549 A1 published Oct. 6, 1999, U.S. Pat. No. 6,417,425
issued Jul. 9, 2002, and in U.S. Pat. No. 5,962,068 issued Oct. 5,
1999. In one particular method, namely an in-situ polymerization
super-absorbent coating process, a super-absorbent monomer solution
containing monomer, crosslinkers and initiators is sprayed onto the
substrate, the sprayed substrate is exposed to UV radiation and/or
other radiation in order to polymerize and crosslink the monomer,
and the irradiated substrate is then exposed to heat to remove any
remaining moisture. In another method, the nonwoven is coated on
one or both sides, with the super-absorbent polymer either
completely covering the nonwoven or covering the nonwoven only in
discreet areas with the super-absorbent polymer containing
activatable cross-linkers which are activated to cross-link the
super-absorbent polymer.
[0026] Suitable super-absorbent polymers may include, for example,
alkali metal salts of polyacrylic acids; polyacrylamides; polyvinyl
alcohol; ethylene maleic anhydride copolymers; polyvinyl ethers;
hydroxypropylcellulose; polyvinyl morpholinone; polymers and
copolymers of vinyl sulfonic acid, polyacrylates, polyacrylamides,
polyvinyl pyridine; and the like. Other suitable polymers include
hydrolyzed acrylonitrile grafted starch, acrylic acid grafted
starch, and isobutylene maleic anhydride copolymers and mixtures
thereof. Other suitable super-absorbent polymers may comprise
inorganic polymers such as polyphosphazene and the like. Further
details on super-absorbent materials may be found in U.S. Pat. No.
4,500,351 issued Feb. 19, 1985 to Peniak et al, using ISOBAM 18
available from the Kuraray America, Inc. of New York, N.Y., and
diethylene triamine cross-linker, or the emulsion method of PCT
Publication No. WO 00/50096 published Aug. 31, 2000 by Gartner et
al., or using a suitable mixture of monomer, cross-linker, and
initiators per the teachings in U.S. Pat. No. 6,417,425 to Whitmore
et al., or the method of U.S. Pat. No. 5,962,068 issued Oct. 5,
1999 wherein the redox initiated polymerizing superabsorbent is
applied to the fibers.
[0027] Generally, the carrier fluids of the present invention are
suitable for use in hydraulic fracturing, frac-packing, and gravel
packing applications. In exemplary embodiments of the present
invention where the carrier fluids are used to carry proppant, the
proppant particles are generally of a size such that formation
fines that may migrate with produced fluids are prevented from
being produced from the subterranean zone. Any suitable proppant
may be used, including graded sand, bauxite, ceramic materials,
glass materials, nut shell, composite polymer beads, and the like.
Generally, the proppant particles have a size in the range of from
about 4 to about 400 mesh, U.S. Sieve Series. In some embodiments
of the present invention, the proppant is graded sand having a
particle size in the range of from about 10 to about 70 mesh, U.S.
Sieve Series.
[0028] In particular embodiments of the present invention, the
proppant may be at least partially coated with a curable resin. In
particular embodiments, this resin-coated proppant ("RCP") may
comprise proppant that has been pre-coated by a commercial
supplier. Suitable commercially available RCP materials include,
but are not limited to, pre-cured resin-coated sand, curable
resin-coated sand, curable resin-coated ceramics, single-coat,
dual-coat, or multi-coat resin-coated sand, ceramic, or bauxite.
Some examples available from Borden Chemical, Columbus, Ohio, are
"XRTTM.RTM. CERAMAX P," "CERAMAX I," "CERAMAX P," "ACFRAC BLACK,"
"ACFRAC CR," "ACFRAC SBC," "ACFRAC SC," and "ACFRAC LTC." Some
examples available from Santrol, Fresno, Tex., Are "HYPERPROP G2,"
"DYNAPROP G2," "MAGNAPROP G2," "OPTIPROP G2," "SUPER HS," "SUPER
DC," "SUPER LC," and "SUPER HT."
[0029] Particular embodiments may also include proppant that is
coated on-the-fly with a curable resin. The term "on-the-fly" is
used herein to mean that a flowing stream is continuously
introduced into another flowing stream so that the streams are
combined and mixed while continuing to flow as a single stream as
part of the on-going treatment. Coating the proppant particles with
the curable resin composition and mixing the resin-treated proppant
particles with the fracturing fluid may all be performed
on-the-fly. Such mixing may also be described as "real-time"
mixing. On-the-fly mixing, as opposed to batch or partial batch
mixing, may reduce waste and simplify subterranean treatments. This
is due, in part, to the fact that if the components are mixed and
then circumstances dictate that the subterranean treatment be
stopped or postponed, the mixed components may quickly become
unusable. By having the ability to rapidly shut down the mixing of
streams on-the-fly, unnecessary waste may be avoided, resulting in,
inter alia, increased efficiency and cost savings.
[0030] Suitable curable resin compositions include those resins
that are capable of forming a hardened, consolidated mass. Suitable
resins include, but are not limited to, two-component epoxy-based
resins, novolak resins, polyepoxide resins, phenol-aldehyde resins,
urea-aldehyde resins, urethane resins, phenolic resins,
furan/furfuryl alcohol resins, phenolic/latex resins, phenol
formaldehyde resins, polyester resins and hybrids and copolymers
thereof, polyurethane resins and hybrids and copolymers thereof,
acrylate resins, and mixtures thereof. Some suitable resins, such
as epoxy resins, may be of the two-component variety mentioned
above and use an external catalyst or activator. Other suitable
resins, such as furan resins generally require a time-delayed
catalyst or an external catalyst to help activate the
polymerization of the resins if the cure temperature is low (i.e.,
less than 250.degree. F.), but will cure under the effect of time
and temperature if the formation temperature is above about
250.degree. F. preferably above about 300.degree. F. Selection of a
suitable resin coating material may be affected by the temperature
of the subterranean formation to which the fluid will be
introduced. By way of example, for subterranean formations having a
bottom hole static temperature ("BHST") ranging from about
60.degree. F. to about 250.degree. F. two-component epoxy-based
resins comprising a hardenable resin component and a hardening
agent component containing specific hardening agents may be
preferred. For subterranean formations having a BHST ranging from
about 300.degree. F. to about 600.degree. F. a furan-based resin
may be preferred. For subterranean formations having a BHST ranging
from about 200.degree. F. to about 400.degree. F. either a
phenolic-based resin or a one-component HT epoxy-based resin may be
suitable. For subterranean formations having a BHST of at least
about 175.degree. F. a phenol/phenol formaldehyde/furfuryl alcohol
resin also may be suitable. It is within the ability of one skilled
in the art, with the benefit of this disclosure, to select a
suitable resin for use in embodiments of the present invention and
to determine whether a catalyst is required to trigger curing.
[0031] Proppant used in accordance with the present invention may
also be at least partially coated with a tackifying agent, in
addition to any resin that may or may not be present. The
tackifying agent may act, inter alia, to enhance the grain-to-grain
contact between individual proppant particles and is believed to
soften any partially cured resin that may be on the proppant
particles. This dual action of the tackifying agent may improve the
final consolidation strength of a proppant pack made in accordance
with the present invention.
[0032] Similar to the application of a curable resin, the
tackifying agent may be applied either on-the-fly or as a pre-coat.
When used in conjunction with RCP, the tackifying agent is
typically applied subsequent to the application of the resin.
Compositions suitable for use as tackifying agents in accordance
with the present invention comprise any compound that, when in
liquid form or in a solvent solution, will form a non-hardening
coating upon a proppant particle. In particular embodiments,
tackifying agents may include polyamides that are liquids or in
solution at the temperature of the subterranean formation such that
they are, by themselves, non-hardening when introduced into the
subterranean formation. One such compound is a condensation
reaction product comprised of commercially available polyacids and
a polyamine. Such commercial products include compounds such as
mixtures of C.sub.36 dibasic acids containing some trimer and
higher oligomers and also small amounts of monomer acids produced
from fatty acids, maleic anhydride, and acrylic acid, and the like.
Such acid compounds are commercially available from companies such
as Witco Corporation, Union Camp, Chemtall, and Emery Industries.
The reaction products are available from, for example, Champion
Technologies, Inc., and Witco Corporation. Additional compounds
which may be used as tackifying agents include liquids and
solutions of, for example, polyesters, polycarbonates and
polycarbamates, natural resins such as shellac, and the like.
Suitable tackifying agents are described in U.S. Pat. No. 5,853,048
issued to Weaver, et al., and U.S. Pat. No. 5,833,000 issued to
Weaver, et al., the relevant disclosures of which are herein
incorporated by reference.
[0033] Tackifying agents suitable for use in the present invention
may be either used such that they form non-hardening coating or
they may be combined with a multifunctional material capable of
reacting with the tackifying compound to form a hardened coating. A
"hardened coating" as used herein means that the reaction of the
tackifying compound with the multifunctional material will result
in a substantially non-flowable reaction product that exhibits a
higher compressive strength in a consolidated agglomerate than the
tackifying compound alone with the particulates. In this instance,
the tackifying agent may function similarly to a hardenable resin.
Multifunctional materials suitable for use in the present invention
include, but are not limited to, aldehydes such as formaldehyde,
dialdehydes such as glutaraldehyde, hemiacetals or aldehyde
releasing compounds, diacid halides, dihalides such as dichlorides
and dibromides, polyacid anhydrides such as citric acid, epoxides,
furfuraldehyde, glutaraldehyde or aldehyde condensates and the
like, and combinations thereof. In some embodiments of the present
invention, the multifunctional material may be mixed with the
tackifying compound in an amount of from about 0.01 to about 50
percent by weight of the tackifying compound to effect formation of
the reaction product. In some preferable embodiments, the compound
is present in an amount of from about 0.5 to about 1 percent by
weight of the tackifying compound. Suitable multifunctional
materials are described in U.S. Pat. No. 5,839,510 issued to
Weaver, et al., the relevant disclosure of which is herein
incorporated by reference.
[0034] Therefore, the present invention is well adapted to attain
the ends and advantages mentioned as well as those that are
inherent therein. While numerous changes may be made by those
skilled in the art, such changes are encompassed within the spirit
of this invention as defined by the appended claims.
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