U.S. patent application number 11/926202 was filed with the patent office on 2008-02-21 for compositions and methods for plugging and sealing a subterranean formation.
Invention is credited to Eldon D. Dalrymple, Larry S. Eoff, Don M. Everett.
Application Number | 20080045423 11/926202 |
Document ID | / |
Family ID | 36101704 |
Filed Date | 2008-02-21 |
United States Patent
Application |
20080045423 |
Kind Code |
A1 |
Everett; Don M. ; et
al. |
February 21, 2008 |
Compositions and Methods for Plugging and Sealing a Subterranean
Formation
Abstract
The invention provides for a composition for treating a
subterranean formation, the composition comprising a
water-swellable agent and a sealing agent. Preferably, the
water-swellable agent: i) absorbs greater than 100 weight % of
water; and ii) swells to greater than 100 weight % as it absorbs
water. Preferably the sealing agent: i) is greater than 0.01 weight
% soluble in water; and ii) forms a three dimensional gel structure
in water. The invention also provides for a method of treating a
subterranean formation penetrated by a wellbore, the method
comprising the steps of: a) introducing a sealing agent into the
subterranean formation; and b) introducing a water-swellable agent
into the subterranean formation.
Inventors: |
Everett; Don M.; (Houston,
TX) ; Eoff; Larry S.; (Duncan, OK) ;
Dalrymple; Eldon D.; (Duncan, OK) |
Correspondence
Address: |
Robert A. Kent, Customer No. 71407;Halliburton Energy Services, Inc.
2600 S. 2nd Street
Duncan
OK
73536-0440
US
|
Family ID: |
36101704 |
Appl. No.: |
11/926202 |
Filed: |
October 29, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11048583 |
Feb 1, 2005 |
7287586 |
|
|
11926202 |
Oct 29, 2007 |
|
|
|
Current U.S.
Class: |
507/226 |
Current CPC
Class: |
Y10S 507/903 20130101;
C09K 8/514 20130101; C09K 8/512 20130101; C09K 8/5083 20130101 |
Class at
Publication: |
507/226 |
International
Class: |
C09K 8/588 20060101
C09K008/588 |
Claims
1. A composition for treating a subterranean formation, the
composition comprising: a water-swellable agent; and a sealing
agent comprising a monomer, wherein the sealing agent is at least
about 0.01 weight % soluble in water and is capable of forming a
three dimensional gel structure in water.
2. The composition of claim 1, wherein the water-swellable agent
comprises at least one water-swellable agent selected from the
group consisting of: a crosslinked polyacrylamide; a crosslinked
polyacrylate; a copolymer of acrylamide and acrylate monomers; a
starch backbone grafted with acrylonitrile and acrylate; a polymer
of two or more of allylsulfonate,
2-acrylamido-2-methyl-1-propanesulfonic acid,
3-allyloxy-2-hydroxy-1-propane-sulfonic acid, acrylamide, and
acrylic acid monomers; a hydrolyzed polyacrylonitrile; a
carboxyalkyl cellulose; a carboxymethyl starch; a salt of
carboxymethyl cellulose; a carboxyalkyl polysaccharide; a
crystalline polymer of a crosslinked polyacrylamide; and any
combination thereof.
3. The composition of claim 1, wherein the sealing agent comprises:
a polymerizable water-soluble vinyl monomer; a multifunctional
vinyl monomer capable of polymerizing and crosslinking; and a
water-soluble azo initiator.
4. The composition of claim 1, wherein the sealing agent comprises:
a non-acidic ethylenically unsaturated polar monomer; a
copolymerizable ethylenically unsaturated ester; and at least one
organic gelling agent selected from the group consisting of: a
polyalkylenimine; a polyfunctional aliphatic amine; an
aralkylamine; a heteroaralkylamine; and any combination
thereof.
5. The composition of claim 1, wherein the sealing agent is at
least about 0.01 weight % soluble in water; and the sealing agent
is capable of forming a three dimensional gel structure in
water.
6. A composition for treating a subterranean formation, the
composition comprising: a water-swellable agent that is capable of
absorbing at least about 100 weight % of water and is capable of
swelling at least about 100 weight % when it absorbs water; and a
sealing agent comprising a monomer.
7. The composition of claim 6, wherein the water-swellable agent
comprises at least one water-swellable agent selected from the
group consisting of: a crosslinked polyacrylamide; a crosslinked
polyacrylate; a copolymer of acrylamide and acrylate monomers; a
starch backbone grafted with acrylonitrile and acrylate; a polymer
of two or more of allylsulfonate,
2-acrylamido-2-methyl-1-propanesulfonic acid,
3-allyloxy-2-hydroxy-1-propane-sulfonic acid, acrylamide, and
acrylic acid monomers; a hydrolyzed polyacrylonitrile; a
carboxyalkyl cellulose; a carboxymethyl starch; a salt of
carboxymethyl cellulose; a carboxyalkyl polysaccharide; a
crystalline polymer of a crosslinked polyacrylamide; and any
combination thereof.
8. The composition of claim 6, wherein the sealing agent comprises:
a polymerizable water-soluble vinyl monomer; a multifunctional
vinyl monomer capable of polymerizing and crosslinking; and a
water-soluble azo initiator.
9. The composition of claim 6, wherein the sealing agent comprises:
a non-acidic ethylenically unsaturated polar monomer; a
copolymerizable ethylenically unsaturated ester; and at least one
organic gelling agent selected from the group consisting of: a
polyalkylenimine; a polyfunctional aliphatic amine; an
aralkylamine; a heteroaralkylamine; and any combination
thereof.
10. The composition of claim 6, wherein the sealing agent is at
least about 0.01 weight % soluble in water; and the sealing agent
is capable of forming a three dimensional gel structure in
water.
11. A composition for treating a subterranean formation, the
composition comprising: a water-swellable agent; and a sealing
agent comprising a monomer.
12. The composition of claim 11, wherein the water-swellable agent
comprises at least one water-swellable agent selected from the
group consisting of: a crosslinked polyacrylamide; a crosslinked
polyacrylate; a copolymer of acrylamide and acrylate monomers; a
starch backbone grafted with acrylonitrile and acrylate; a polymer
of two or more of allylsulfonate,
2-acrylamido-2-methyl-1-propanesulfonic acid,
3-allyloxy-2-hydroxy-1-propane-sulfonic acid, acrylamide, and
acrylic acid monomers; a hydrolyzed polyacrylonitrile; a
carboxyalkyl cellulose; a carboxymethyl starch; a salt of
carboxymethyl cellulose; a carboxyalkyl polysaccharide; a
crystalline polymer of a crosslinked polyacrylamide; and any
combination thereof.
13. The composition of claim 11, wherein the sealing agent
comprises: a polymerizable water-soluble vinyl monomer; a
multifunctional vinyl monomer capable of polymerizing and
crosslinking; and a water-soluble azo initiator.
14. The composition of claim 11, wherein the sealing agent
comprises: a non-acidic ethylenically unsaturated polar monomer; a
copolymerizable ethylenically unsaturated ester; and at least one
organic gelling agent selected from the group consisting of: a
polyalkylenimine; a polyfunctional aliphatic amine; an
aralkylamine; a heteroaralkylamine; and any combination
thereof.
15. The composition of claim 11, wherein the water-swellable agent
is capable of absorbing at least about 100 weight % of water; and
the water-swellable agent is capable of swelling at least about 100
weight % when it absorbs water.
16. The composition of claim 11, wherein the sealing agent is at
least about 0.01 weight % soluble in water; and the sealing agent
is capable of forming a three dimensional gel structure in
water.
17. A composition for treating a subterranean formation, the
composition comprising: a water-swellable agent comprising at least
one water-swellable agent selected from the group consisting of: a
crosslinked polyacrylamide; a crosslinked polyacrylate; a copolymer
of acrylamide and acrylate monomers; a starch backbone grafted with
acrylonitrile and acrylate; a polymer of two or more of
allylsulfonate, 2-acrylamido-2-methyl-1-propanesulfonic acid,
3-allyloxy-2-hydroxy-1-propane-sulfonic acid, acrylamide, and
acrylic acid monomers; a hydrolyzed polyacrylonitrile; a
carboxyalkyl cellulose; a carboxymethyl starch; a salt of
carboxymethyl cellulose; a carboxyalkyl polysaccharide; a
crystalline polymer of a crosslinked polyacrylamide; and any
combination thereof; and a sealing agent comprising a monomer.
18. The composition of claim 17, wherein the sealing agent
comprises: a polymerizable water-soluble vinyl monomer; a
multifunctional vinyl monomer capable of polymerizing and
crosslinking; and a water-soluble azo initiator.
19. The composition of claim 17, wherein the sealing agent
comprises: a non-acidic ethylenically unsaturated polar monomer; a
copolymerizable ethylenically unsaturated ester; and at least one
organic gelling agent selected from the group consisting of: a
polyalkylenimine; a polyfunctional aliphatic amine; an
aralkylamine; a heteroaralkylamine; and any combination
thereof.
20. The composition of claim 17, wherein the water-swellable agent
is capable of absorbing at least about 100 weight % of water; and
the water-swellable agent is capable of swelling at least about 100
weight % when it absorbs water.
21. The composition of claim 17, wherein the sealing agent is at
least about 0.01 weight % soluble in water; and the sealing agent
is capable of forming a three dimensional gel structure in
water.
22. A composition for treating a subterranean formation, the
composition comprising: a water-swellable agent; and a sealing
agent comprising: a non-acidic ethylenically unsaturated polar
monomer; a copolymerizable ethylenically unsaturated ester; and at
least one organic gelling agent selected from the group consisting
of: a polyalkylenimine; a polyfunctional aliphatic amine; an
aralkylamine; a heteroaralkylamine; and any combination
thereof.
23. The composition of claim 22, wherein the water-swellable agent
comprises at least one water-swellable agent selected from the
group consisting of: a crosslinked polyacrylamide; a crosslinked
polyacrylate; a copolymer of acrylamide and acrylate monomers; a
starch backbone grafted with acrylonitrile and acrylate; a polymer
of two or more of allylsulfonate,
2-acrylamido-2-methyl-1-propanesulfonic acid,
3-allyloxy-2-hydroxy-1-propane-sulfonic acid, acrylamide, and
acrylic acid monomers; a hydrolyzed polyacrylonitrile; a
carboxyalkyl cellulose; a carboxymethyl starch; a salt of
carboxymethyl cellulose; a carboxyalkyl polysaccharide; a
crystalline polymer of a crosslinked polyacrylamide; and any
combination thereof.
24. The composition of claim 22, wherein the water-swellable agent
is capable of absorbing at least about 100 weight % of water; and
the water-swellable agent is capable of swelling at least about 100
weight % when it absorbs water.
25. The composition of claim 22, wherein the sealing agent is at
least about 0.01 weight % soluble in water; and the sealing agent
is capable of forming a three dimensional gel structure in water.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional patent application of
commonly-owned U.S. patent application Ser. No. 11/048,583, filed
Feb. 1, 2005, entitled "Compositions and Method for Plugging and
Sealing a Subterranean Formation," by Everett et al., which is
incorporated by reference herein for all purposes.
BACKGROUND
[0002] There has been a continuing and long-felt need for improving
the oil/water ratio during hydrocarbon production by using chemical
gel systems to resist the flow of injected or natural aqueous drive
fluid through high permeability channels and fractures. This is
sometimes referred to in the art as "conformance control." The
general approach has been to inject a mixture of reagents,
initially low in viscosity, into a zone of the formation that has
high permeability. After a sufficient time to allow the mixture to
be pumped into the subterranean formation or when exposed to the
elevated temperature of the formation, the mixture of reagents then
forms a gel to block the flow of water. Several mixtures of
reagents have been used in this way.
[0003] For example, U.S. Pat. No. 4,600,057 entitled "Method of
Reducing the Permeability of a Subterranean Formation" issued Jul.
15, 1986, and having named inventor John K. Borchardt, discloses a
method of reducing the permeability of a subterranean formation
comprising contacting the formation with an aqueous polymerizable
composition comprising a polymerization monomer, a polymerization
catalyst having a latent period, and an alcoholic compound selected
from the group consisting of a cyclic ether containing a
hydroxymethylene substituent on a carbon atom bonded to the ether
oxygen, an aliphatic alcohol having a carbon-to-carbon double bond
or a carbon-to-carbon triple bond, and mixtures thereof. See
Abstract. U.S. Pat. No. 4,600,057 is incorporated herein by
reference in its entirety.
[0004] U.S. Pat. No. 4,640,361 entitled "Thermally Responsive
Aqueous Silicate Mixtures and Use Thereof" issued Feb. 3, 1987, and
having named inventors William H. Smith and Edward F. Vinson,
discloses a thermally responsive aqueous silicate composition
consisting essentially of an aqueous solution containing an alkali
metal silicate and a thermally responsive silicate gelation
activator. The thermally responsive silicate gelation activator is
a reducing sugar selected from the group consisting of lactose,
dextrose, fructose, galactose, mannose, maltose, xylose and
mixtures thereof. The aqueous silicate composition can be utilized
in treating a subterranean formation for the purpose of sealing the
formation. See Abstract. U.S. Pat. No. 4,640,361 is incorporated
herein by reference in its entirety.
[0005] U.S. Pat. No. 5,168,928 entitled "Preparation and Use of
Gelable Silicate Solutions in Oil Field Applications" issued Dec.
8, 1992, and having named inventors Dralen T. Terry and Edward F.
Vinson, discloses a gelable silicate solution prepared by mixing
fumed silica and an alkali metal hydroxide with water. The silicate
solution is used to form a seal or plug in one or more subterranean
formations or in a well bore penetrating the formations by pumping
the solution into a desired location in the well bore or formations
and allowing the silicate solution to gel therein. See Abstract.
U.S. Pat. No. 5,168,928 is incorporated herein by reference in its
entirety.
[0006] U.S. Pat. No. 5,320,171 entitled "Method of Preventing Gas
Coning and Fingering in a High Temperature Hydrocarbon Bearing
Formation" issued Jun. 14, 1994, and having named inventor Mary A.
H. Laramay, discloses a method of preventing gas coning or
fingering from a gas cap in an oil producing well. A silicate
solution and a delayed activator are injected into the gas cap
under conditions such that the activator causes the silicate to gel
after a predetermined period of time to form a substantially
impermeable zone or layer above the oil bearing formation to
prevent gas from flowing into the oil well during production. See
Abstract. U.S. Pat. No. 5,320,171 is incorporated herein by
reference in its entirety.
[0007] U.S. Pat. No. 5,335,726 entitled "Water Control" issued Aug.
9, 1994, and having named inventor Klein A. Rodrigues, discloses a
method of forming a gel in a subsurface formation whereby a monomer
is polymerized in the formation in the presence of a crosslinker by
an initiator selected from azo compounds which are temperature
activated over a range of temperatures. The method is particularly
useful to substantially terminate or at least decrease the flow of
water from a subterranean formation into a wellbore penetrating the
formation. See Abstract. U.S. Pat. No. 5,335,726 is incorporated
herein by reference in its entirety.
[0008] U.S. Pat. No. 5,358,051 entitled "Method of Water Control
with Hydroxy Unsaturated Carbonyls" issued Oct. 25, 1994, and
having named inventor Klein A. Rodrigues, discloses a method of
forming a gel in the subsurface formation whereby a self
crosslinking monomer selected from hydroxy unsaturated carbonyl
compounds is polymerized in the formation by a suitable initiator.
In a preferred embodiment, the initiator is selected from azo
compounds which are temperature activated over a range of
temperatures. The method is particularly useful to substantially
terminate or at least decrease the flow of water from a
subterranean formation into a wellbore penetrating the formation.
See Abstract. U.S. Pat. No. 5,358,051 is incorporated herein by
reference in its entirety. Without being limited by theory, it is
now believed that the monomer is not self-crosslinking, rather, it
is the difunctional monomeric by-product that causes the
crosslinking,
[0009] U.S. Pat. No. 5,836,392 entitled "Oil And Gas Field
Chemicals" issued Nov. 17, 1998, and having named inventor Phillip
Lance Urlwin-Smith, discloses a method for conformance control of a
reservoir comprising injecting into a zone of the reservoir an
aqueous solution of a co-polymer comprising at least one
ethylenically unsaturated polar monomer and at least one
copolymerizable ethylenically unsaturated ester formed from a
hydroxy compound of the formula ROH wherein R is a selected alkyl
group, alkenyl group, cycloalkyl group, aryl group or such groups
substituted with from 1 to 3 hydroxy, ether or thio ether groups or
a heterocyclic or selected heterocyclic alkylene group and at least
one heteroatom selected from oxygen, nitrogen and sulfur and a
selected alkenoic or aralkenoic carboxylic acid or sulfonic or
phosphoric acid together with a crosslinking agent comprising a
multi-valent metal ion capable of crosslinking an acrylic acid
polymer to form a viscous gel. The injected fluid is flowed through
at least a portion of a high permeability region within said zone
wherein it is heated to an elevated temperature whereupon
crosslinking of the polymers occurs to form a substantially
non-flowable gel within said high permeability region. The
crosslinking of the injected fluid to form the non-flowable gel
within the formation reduces the permeability of said region in
said zone. See Abstract. U.S. Pat. No. 5,836,392 is incorporated
herein by reference in its entirety.
[0010] U.S. Pat. No. 6,187,839 entitled "Methods of Sealing
Compositions and Methods" issued Feb. 13, 2001, and having named
inventors Larry Eoff and David Brown, provides methods of sealing
subterranean zones using high density sealing compositions. The
methods are basically comprised of introducing a sealing
composition into the subterranean zone comprised of a high density
aqueous salt solution, a polymerizable monomer and a polymerizable
initiator and allowing said sealing composition to form a sealing
gel in said zone. See Abstract. U.S. Pat. No. 6,187,839 is
incorporated herein by reference in its entirety.
[0011] U.S. Pat. No. 6,192,986 entitled "Blocking Composition For
Use In Subterranean Formation," issued Feb. 27, 2001, and having
named inventor Phillip Lance Urlwin-Smith, discloses a polymer
composition for pumping downhole to gel in a subterranean formation
comprising a water-soluble copolymer of (i) at least one non-acidic
ethylenically unsaturated polar monomer and (ii) at least one
copolymerizable ethylenically unsaturated ester; and an organic
gelling agent therefor. See Abstract. U.S. Pat. No. 6,192,986 is
incorporated herein by reference in its entirety.
[0012] U.S. patent application Ser. No. 10/826,615, entitled "Well
Treatment Fluid and Methods for Blocking Permeability of a
Subterranean Zone," filed Apr. 16, 2004, by the assignee of the
present invention, discloses a well treatment fluid for use in a
well, the well treatment fluid comprising water, a water-soluble
polymer comprising at least one unit of vinyl amine, and an organic
compound that is crosslinked with the polymer. It also discloses a
method of treating a subterranean formation penetrated by a
wellbore, the method comprising the steps of: (a) forming a
treatment fluid comprising water, a water-soluble polymer
comprising at least one unit of vinyl amine, and an organic
compound that is crosslinked with the polymer; and (b) introducing
the treatment fluid through the wellbore and into contact with the
formation. See Abstract. U.S. patent application Ser. No.
10/826,615 is herein incorporated by reference in its entirety.
[0013] The above compositions, however, often experience such a
long delay in developing high viscosity that the composition are
excessively diluted and displaced more deeply into the formation
than desired. Consequently, the compositions may pass completely
through highly permeable fractures, vugs and the like, instead of
blocking them.
SUMMARY OF THE INVENTION
[0014] The invention provides for a composition for treating a
subterranean formation, the composition comprising a
water-swellable agent and a sealing agent. Preferably, the
water-swellable agent: i) absorbs greater than 100 weight % of
water; and ii) swells to greater than 100 weight % as it absorbs
water. Preferably the sealing agent: i) is greater than 0.01 weight
% soluble in water; and ii) forms a three dimensional gel structure
in water.
[0015] The invention also provides for a method of treating a
subterranean formation penetrated by a wellbore, the method
comprising the steps of: a) introducing a sealing agent into the
subterranean formation; and b) introducing a water-swellable agent
into the subterranean formation. These steps can be performed
simultaneously or separately.
[0016] These and other aspects of the invention will be apparent to
one skilled in the art upon reading the following detailed
description. While the invention is susceptible to various
modifications and alternative forms, specific embodiments thereof
will be described in detail and shown by way of example. It should
be understood, however, that it is not intended to limit the
invention to the particular forms disclosed, but, on the contrary,
the invention is to cover all modifications and alternatives
falling within the spirit and scope of the invention as expressed
in the appended claims.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0017] In addition to the prior art discussed in the Background of
the Invention, another method for controlling the production of
natural and injection fluid in subterranean formations includes the
use of water-swellable polymers. For example, water-swellable
polymers are disclosed in U.S. patent application Ser. No.
10/375,205, filed Feb. 27, 2003, entitled, "Methods For Passing A
Swelling Agent Into A Reservoir To Block Undesirable Flow Paths
During Oil Production," assigned to the assignee of the invention,
which is incorporated by reference in its entirety. Like the
sealing and/or blocking compositions mentioned in the Background of
the Invention, such water-swellable polymers possess the capacity
to form gel masses that resist unwanted fluid flow through the
formation. The resultant gel masses readily penetrate into
fractures of a subterranean formation if the gel masses are of a
suitable size. The size of the resultant gel masses depends on the
particle size of the dry polymeric material prior to hydration.
These properties allow the gelled polymer particles to be packed
into the formation voids, forming a seal within the formation.
[0018] Unfortunately, the hydrated gel masses of such
water-swellable agents exhibit little in the way of cohesive
properties, which significantly limits their ability to form
substantial, durable, in situ seals. Further, such agents are held
against the formation's surface primarily by frictional or
interference forces. If sufficient hydrostatic pressure is exerted
upon these seals, fluid may pass between the gelled polymer
particles and continue to escape into the formation.
[0019] It has been discovered that by combining a water-swellable
agent together with a sealing agent, a more cohesive gel system can
be obtained for treating a subterranean formation. A method of use
includes the steps of introducing both a water-swellable agent and
a sealing agent through a well into a subterranean formation. Such
a well treatment composition is capable of forming a more durable,
hydrostatic pressure-resistant seal that substantially reduces or
blocks the flow path of fluid through a zone in a subterranean
formation.
[0020] The term "water-swellable agent" is generally used to refer
to an agent that is capable of swelling in the presence of water.
As used herein, the term is specifically defined to mean an agent
that swells (i.e., expands) as it absorbs water to at least two (2)
times its original mass. Preferably, the water-swellable agent: i)
absorbs greater than 100 weight % of water; and ii) swells to
greater than 100 weight % as it absorbs water. Preferably the
sealing agent: i) is greater than 0.01 weight % soluble in water;
and ii) forms a three dimensional gel structure in water.
Preferably, the water-swellable agent has these properties of
absorbing and swelling at standard temperature and pressure. Also,
the sealing agent preferably has these properties of solubility at
standard temperature and pressure. Without being limited by any
theoretical explanation, it is believed that because the
water-swellable agent is so insoluble in water, it does not become
diluted and washed away by water or other aqueous injectants
flowing through the formation.
[0021] Examples of water-swellable agents include crosslinked
polyacrylamide, crosslinked polyacrylate, copolymers of acrylamide
and acrylate monomers, a starch backbone grafted with acrylonitrile
and acrylate, polymers of two or more of allylsulfonate,
2-acrylamido-2-methyl-1-propanesulfonic acid,
3-allyloxy-2-hydroxy-1-propane-sulfonic acid, acrylamide, and
acrylic acid monomers, and any combination in any proportion of the
foregoing. The water-swellable agent is preferably a crystalline
polymer that has been dehydrated. One preferred water-swellable
agent is crosslinked polyacrylamide in the form of a hard crystal.
Still other examples of water-swellable agents include hydrolyzed
polyacrylonitrile, carboxyalkyl cellulose, carboxymethyl starch,
salts of carboxymethyl cellulose, carboxyalkyl polysaccharide, and
any combination in any proportion of the foregoing. Further
water-swellable agents are described in European Patent No.
0566118, filed Apr. 14, 1993, by inventor Jian Qin, which is
incorporated herein by reference in its entirety.
[0022] Preferably, the water-swellable agent comprises a
superabsorbent. Superabsorbents are swellable crosslinked polymers
that have the ability to absorb and store at least multiples of
their own weight of aqueous liquids by forming a gel.
Superabsorbents retain the water that they absorb and typically do
not release the water, even under pressure. Examples of
superabsorbents are sodium acrylate-based polymers having three
dimensional, network-like molecular structures. The polymer chains
are formed by the reaction/joining of units of acrylic acid
monomer, which have been substantially neutralized with sodium
hydroxide (caustic soda). Crosslinking units of acrylic acid
monomer form a three-dimensional network, enabling the
superabsorbent to absorb water into the spaces in the
three-dimensional network, and thus forming a gel and locking up
water.
[0023] Preferably, as the water-swellable agent absorbs water, its
physical size increases by about 10 to 400 times its original size.
The amount and rate by which the water-swellable agent increases in
size can vary depending upon temperature, grain size, and the ionic
strength of the carrier fluid. Because the temperature of a well
generally increases from top to bottom, the rate of swelling tends
to increase as the water-swellable agent is pumped downhole. The
rate of swelling also increases as the grain size of the
water-swellable agent decreases and as the ionic strength of the
carrier fluid decreases. For example, the size of the crosslinked
polyacrylamide polymer in a 14 mm grind size increases by 0% in 20
minutes after contacting water, 150% in 35 minutes after contacting
water, and 400% in 45 minutes after contacting water at 80.degree.
F. The size of the crosslinked polyacrylamide polymer increases by
0% in 15 minutes after contacting water, 200% in 25 minutes after
contacting water, and 400% in 35 minutes after contacting water at
145.degree. F. The mass of the crosslinked polyacrylamide polymer
increases by 0% in 45 minutes after contacting 9.2 pounds/gallon
(ppg) Brine Water, 25% in 60 minutes after contacting 9.2 ppg Brine
Water, and 50% in 75 minutes after contacting 9.2 ppg Brine Water
at 80.degree. F. The mass of the crosslinked polyacrylamide polymer
increases by 0% in 30 minutes after contacting 9.2 ppg Brine Water,
25% in 45 minutes after contacting 9.2 ppg Brine Water, and 50% in
60 minutes after contacting 9.2 ppg Brine Water at 145.degree. F.
Other scientific data regarding swellable polymers is illustrated
in application Ser. No. 10/375,203, filed Feb. 27, 2003, which is
assigned to the assignee of the present invention, and incorporated
herein by reference in its entirety; application Ser. No.
10/375,183, filed Feb. 27, 2003, also assigned to the assignee of
the present invention, and incorporated herein by reference in its
entirety; and application Ser. No. 10/233,038, also assigned to the
assignee of the present invention, and incorporated herein by
reference in its entirety.
[0024] While downhole, the water-swellable agent begins to absorb
the water and swell into a gel mass that is substantially resistant
to the flow of fluid, diminishing the flow into/through the
fractures, vugs, voids, fissures, and high permeability streaks
through which aqueous fluids could otherwise pass unrestricted. The
gel mass can withstand a relatively large amount of pressure and
thus resists being dislodged from its position during subsequent
placement of the sealant.
[0025] The invention provides introducing the sealing agent into
the subterranean formation and subsequently introducing the
water-swellable agent into the subterranean formation.
Alternatively, the water-swellable agent can be introduced into the
subterranean formation prior to introducing the sealing agent into
the subterranean formation. Still further, the sealing agent and
swelling agent can be introduced into the subterranean formation
simultaneously. Also, the sealing agent and water-swellable agent
can be mixed together prior to introducing the mixture into the
subterranean formation. As used herein, the term "sealing agent" is
generally used to refer to an agent that is initially capable of
being pumped but after a period of time can form a gel that is not
pumpable. This term does not necessarily require, however, that the
sealing agent form a gel that completely "seals" a porous
formation, but after gelling, the agent should at least resist the
fluid flow through a porous formation. Preferably, the sealing
agent is greater than 0.01 weight % soluble in water, and forms a
gel in water.
[0026] The sealing agent is a composition of one or more chemical
compounds or classes of chemical compounds that can react, for
example, by polymerization and/or crosslinking, to form a material
that gels with water. Optionally, the sealing agent can include a
catalytic agent to promote polymerization and/or crosslinking, or a
catalytic agent can be added later, for example, by over flushing
the sealing agent with a carrier containing the catalytic
agent.
[0027] The reaction of the sealing agent can be delayed to allow
for pumping the sealing agent through a wellbore and into a
subterranean formation. As the temperature of a subterranean
formation is elevated, the increase in temperature can also promote
polymerization and/or crosslinking. For example, some crosslinking
systems are considered to be heat activated.
[0028] Examples of sealing agents that are useful for the present
invention have been incorporated by reference in the above
Background of the Invention.
[0029] Without being limited by any theoretical explanation, in the
case of crosslinked polyacrylamide in the form of a hard crystal,
it is believed that the crosslinked polyacrylamide deflects and
surrounds the water molecules during water absorption. In effect,
as the crosslinked polyacrylamide absorbs water, the crosslinked
polyacrylamide undergoes a change from that of a dehydrated crystal
to that of a hydrated gel. In combination with a sealing agent, it
is believed that some of the sealant is adsorbed by the crosslinked
polyacrylamide (water-swellable agent) within their individual
three dimensional lattice structures, and thus when the sealant
crosslinks or polymerizes, the newly formed gel is a continuous
mass both inside and outside the water-swellable agent, thereby
providing a more cohesive gel mass. In addition, it is believed
that the sealing agent becomes a more concentrated gel mass, and is
better able to "seal" against the formation surface.
[0030] It is further believed that the water-swellable crosslinked
polyacrylamide becomes more pressure resistant in conjunction with
the sealing agent because it acquires a more sticky property.
Similarly, the sealing agent becomes more pressure resistant
because it acquires the voluminous properties of a water-swellable
agent. Because of this synergistic relationship, the
water-swellable agent and the sealing agent form a more durable
seal in a subterranean formation.
[0031] Once fully hydrated, the water-swellable agent and the
sealing agent exhibit a high resistance to the migration of aqueous
fluids through the gel mass. That is, the polymers of the
water-swellable agent and the sealing agent are sufficiently packed
together to substantially inhibit water from passing through the
gel. Further, the gel can effectively seal fractures in the
reservoir because it can withstand substantial amounts of pressure
without being dislodged from the formation's surface. The
relatively low permeability of water and/or other injectant fluids
through the gel-packed formation creates a barrier to the flow of
water through the permeable zone in the subterranean formation.
[0032] As mentioned, the invention provides for a method of
treating a subterranean formation penetrated by a wellbore, the
method comprising the steps of: a) introducing a sealing agent into
the subterranean formation; and b) introducing a water-swellable
agent into the subterranean formation. These steps can be performed
simultaneously or separately. For example, the sealing agent and
the water-swellable agent can be combined to form a mixture that is
then introduced into the subterranean formation.
[0033] An aqueous solution can be introduced into the subterranean
formation before, along with, or after introducing the sealing
agent and/or water-swellable agent into the subterranean formation.
As the aqueous fluid contacts the water-swellable agent, the
water-swellable agent swells to form a gel mass that substantially
plugs one or more of the permeable zones. Preferably, the
water-swellable agent is insoluble in water and thus avoids
becoming diluted and washed away by aqueous fluids and/or
subsequent injectants.
[0034] According to some embodiments, the water-swellable agent can
be combined with a carrier fluid to form a carrier solution before
being placed in a well bore. The carrier fluid can be aqueous or
non-aqueous. The carrier fluid can be any suitable fluid that is
pumpable for moving the water-swellable agent to desired locations
in the reservoir. The water-swellable agent is incorporated in an
effective amount to effectively seal a permeable zone upon being
placed into the subterranean formation, and the effective amount
may vary depending on factors such as the type of the carrier
fluid, the size of a fracture, fissure, and the like. The amount of
water-swellable agent that may be combined with the carrier fluid
depends on a number of factors, including the type of carrier
fluid. In general, the carrier fluid may contain from about 0.001
to about 5.0 pounds water-swellable agent/gallon carrier fluid,
more preferably from about 0.01 to about 2.0 ppg. Preferably, the
carrier fluid containing the water-swellable agent remains
sufficiently non-viscous in order to be displaced to the permeable
areas of the reservoir. Thus, there is no need to apply higher
pressure in an attempt to force the water-swellable agent into the
permeable areas that could damage the rock structure surrounding
the reservoir. Examples of carrier fluids with which the
water-swellable agent may be combined include but are not limited
to fresh water, deionized water, brine water of varying salinity,
chloride solutions such as calcium dichloride and potassium
chloride solutions, hydrocarbons such as produced oil and diesel
oil, and synthetic fluids such as ester or polymer based
fluids.
[0035] The invention can be used in producing wells or injection
wells. The amount of oil production may be monitored to determine
if more water-swellable agent should be added to the reservoir to
block additional permeable areas and thus improve production. If
needed, additional water-swellable agent can be introduced into the
subterranean formation. This procedure may be repeated until the
amount of water-swellable agent is sufficient to achieve the
desired amount of production. In one embodiment, the
water-swellable agent and sealing agent are introduced into one or
more injection wells after termination of the production stage of
the primary well. Secondary and/or tertiary flooding operations may
also be performed by displacing one or more injectants into an
injection well and through the reservoir to drive additional oil
from the reservoir to the production wells. The presence of the
fluid of the invention in the permeable zones serves to
substantially block or seal the flow pathways of the injectants
through the permeable zones. The water-swellable agent and sealing
agent may be introduced into the reservoir concurrently with, or
preferably prior to the displacing injectants. Advantageously,
displacing injectants thus do not prematurely pass through the
permeable zones to the production wells before having been
introduced through areas of the reservoir-containing oil.
[0036] When used in injection applications, the injectant can be
any suitable fluid for causing movement of oil in the flow
direction of the fluids as they pass from an injection well through
a reservoir containing the oil to a production well. Examples of
suitable injectants include fresh water, brine, and gases such as
carbon dioxide. Preferably, an aqueous solution serves as both the
carrier fluid and an injectant. The water-swellable agent may be
introduced to an injectant stream as it is being pumped into an
injection well such that the injectant stream also acts as the
carrier fluid for the swelling agent. Because the injectant/carrier
fluid is an aqueous solution, no additional step is required to
contact the water-swellable agent with an aqueous solution to cause
the water-swellable agent to swell. Alternatively, the carrier
solution can be a non-aqueous solution such as a hydrocarbon, and
the injectant is an aqueous solution. As such, the water-swellable
agent is combined with the carrier solution before displacing the
resulting mixture through an injection well and into the reservoir.
The injectant is then displaced to the reservoir to cause the
water-swellable agent to swell and to drive oil from the reservoir
to the production wells. Alternatively, the carrier solution is a
non-aqueous solution, and the injectant is a gas. After combining
the water-swellable agent with the carrier fluid and passing the
resulting mixture to the reservoir via an injection well, the
aqueous solution is introduced into the injection well so as to
contact the swelling agent. Then the injectant is displaced into
the injection well to drive oil from the reservoir to the
production wells.
[0037] If desired, the swollen water-swellable agent may be removed
from the reservoir or area of placement after it has been used for
its intended purpose. If the water-swellable agent and/or sealing
agent are a polymer, the backbone structure of the polymer may be
broken down such that it becomes more like a liquid. Any known
means may be used to break down or collapse the polymer. For
example, the polymer may be contacted with an oxidizer such as
sodium hypochlorite (i.e., bleach) to eliminate the polymer from
the reservoir, preferably by pumping such compounds down the well
bore and contacting the conglomerated, swollen water-swellable
agent and sealing agent in situ.
[0038] After careful consideration of the specific and exemplary
embodiments of the invention described, a person of ordinary skill
in the art will appreciate that certain modifications,
substitutions and other changes can be made without substantially
deviating from the principles of the invention. The detailed
description is illustrative, the spirit and scope of the invention
being limited only by the appended Claims.
* * * * *