U.S. patent application number 11/712055 was filed with the patent office on 2007-09-06 for preformed particle gel for conformance control in an oil reservoir.
Invention is credited to Hongxin Tang.
Application Number | 20070204989 11/712055 |
Document ID | / |
Family ID | 38470497 |
Filed Date | 2007-09-06 |
United States Patent
Application |
20070204989 |
Kind Code |
A1 |
Tang; Hongxin |
September 6, 2007 |
Preformed particle gel for conformance control in an oil
reservoir
Abstract
Expandable and hydrophilic polymeric particles may be made in a
non-emulsion system, and with controllable hardness and delay in
their time to swell in a fresh or salt water environment. These
particles are prepared from combining monomers, controlled
monomers, stable cross-linkers, initiators, and other agents, in
aqueous solution. The controlled monomers induce kinetically
controllable decomposition, degrading over time, thus inducing a
desired time delay in particle swelling. The delay and degree of
the swelling of the particles is controlled by selection of
controlled monomer, stable cross-linking agents, monomers, and
process conditions. These preformed particle gels are made to an
initial particle size of 0.1 micron in diameter or larger via
different grinding techniques. This composition is used for
modifying the permeability of subterranean formations and thereby
increasing the recovery rate of hydrocarbon fluids present in the
formation.
Inventors: |
Tang; Hongxin; (Covina,
CA) |
Correspondence
Address: |
MICHAEL A. SHIPPEY, PH. D.
4848 LAKEVIEW AVENUE, SUITE B
YORBA LINDA
CA
92886
US
|
Family ID: |
38470497 |
Appl. No.: |
11/712055 |
Filed: |
February 28, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60780950 |
Feb 28, 2006 |
|
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|
Current U.S.
Class: |
166/270 ;
166/295; 166/300; 507/224; 507/225; 507/229; 507/903 |
Current CPC
Class: |
C09K 8/512 20130101;
C09K 8/516 20130101; C09K 8/508 20130101 |
Class at
Publication: |
166/270 ;
166/295; 166/300; 507/225; 507/224; 507/229; 507/903 |
International
Class: |
E21B 43/22 20060101
E21B043/22; E21B 33/138 20060101 E21B033/138 |
Claims
1. A method of conformance control for oil and gas production by
using gel-forming materials comprising preformed particles, wherein
the particles have a controlled delay time before forming a gel and
expanding significantly.
2. The method of claim 1, wherein the size of the preformed
particles ranges from 10 microns to 5 millimeters in diameter.
3. The method of claim 1 wherein the preparation of gels further
comprises forming cross-linked expandable polymeric particles.
4. The method of claim 1, wherein said method further comprises
polymerizing one or more polymerizable monomers, in concentrations
of from about 5 to 60 % of reactants, under free radical
initiator-forming conditions in the presence of about 0.01% to 30%
of controlled monomers and 0 to about 5% of stable cross-linkers in
aqueous solution.
5. The method of claim 4, wherein said method further comprises
agents selected from the group consisting of: bases, reducing
promoters, regulators, stabilizers, chelating agent, thermal
agents, chain-transfer agents, oxygen scavengers, pH adjusters, and
gel strength modifiers, in amounts of from 0 to about 60%.
6. The method of claim 4 wherein the monomer is selected from the
group consisting of: nonionic monomer, anionic monomer, cationic
monomer, zwitterionic monomer, betaine monomer, and amphoteric ion
pair monomer.
7. The method of claim 4 wherein the nonionic monomers are selected
from the group consisting of: vinyl amide, acryloylmorpholine,
acrylate, maleic anhydride, N-vinylpyrrolidone, vinyl acetate,
N-vinyl formamide and their derivatives.
8. The method of claim 4 wherein the nonionic monomers are selected
from the group consisting of: hydroxyethyl (methyl) acrylate
CH2=CR--COO--CH2CH2OH (I) and CH2=CR--CO--N(Z1)(Z2) (2)
N-substituted (methyl)acrylamide (II), wherein R.dbd.H or Me; Z1=H
or 5-15C alkyl; 1-3C alkyl substituted by 1-3 phenyl, phenyl or
6-12C cycloalkyl (both optionally substituted) and Z2=H; Z1 and Z2
are each 3-10C alkyl; (II) is N-tert. hexyl, tert. octyl,
methylundecyl, cyclohexyl, benzyl, diphenylmethyl, triphenyl
Acrylamide; and their derivatives.
9. The method of claim 4 wherein the anionic monomers are salts of
unsaturated organic acids, including acrylic acid, methacrylic
acid, maleic acid, itaconic acid, acrylamido methylpropane sulfonic
acid, vinylphosphonic acid, styrene sulfonic acid and their
derivatives.
10. The method of claim 4 wherein the cationic monomers include
quaternary ammonium and acid salts of vinyl amide, vinyl carboxylic
acid, methacrylate and their derivatives.
11. The method of claim 4 wherein the controlled monomers include:
a. [CR.sub.1R.sub.2.dbd.CR.sub.3--CO-]n esters of di, tri, tetra
alcohols (I); b. [CR.sub.1R.sub.2.dbd.CR.sub.3--O-]n esters of di,
tri, tetra functional acids (II); c.
[CR.sub.1R.sub.2.dbd.CR.sub.3--CR.sub.4R.sub.5--O]n esters of di,
tri, tetra functional acids (III); d.
[CR.sub.1R.sub.2.dbd.CR.sub.3--CO-]m amides (IV); e.
[CR.sub.1R.sub.2.dbd.C R.sub.3--].sub.2 of bisazo (V); f.
[CR.sub.1R.sub.2.dbd.C R.sub.3--CR.sub.4R.sub.5--].sub.2 of bisazo
(VI); and, the derivatives of (I)-(VI), wherein R.sub.1.dbd.H or
Me, R.sub.2.dbd.H or Me, R.sub.3.dbd.H or Me,
R.sub.4.dbd.R.sub.5.dbd.H or Me, n=2, 3, or 4, and m=2, 3, or
4.
12. The method of claim 4 wherein the stable cross-linkers include
aluminum salt, zirconium salt, chromium salt and organic
cross-linkers such as methylenebisacrylamide,
hexamethylenetetramine, and phenol aldehyde.
13. The method of claim 4 wherein the aqueous solution includes
water, buffer solvent, or other non-oil and non-surfactant
solutions and their derivatives.
14. The method of claim 4 wherein the initiators are selected from
the group consisting of: ammonium persulfate, potassium persulfate,
sodium persulfate, sodium bromate, sodium bisulfite, and mixtures
thereof.
15. The method of claim 5 wherein the bases are selected from the
group consisting of: sodium carbonate, sodium bicarbonate, sodium
hydroxide and their derivatives.
16. The method of claim 5 wherein the reducing promoters are
selected from the group consisting of: potassium metabisulfite,
sodium sulfite, thionyl chloride, thionyl bromide and their
derivatives.
17. The method of claim 5, wherein said regulators comprise organic
alcohols.
18. The method of claim 5, wherein the stabilizers are selected
from the group consisting of: phenol, m-dihydroxybenzene, and
hydroquinone.
19. The method of claim 5 wherein the chelating agents are selected
from the group consisting of: ethylene diamine tetra acetate (EDTA)
and the like.
20. The method of claim 5 wherein the thermal agent comprises
2-acrylamido-2-methyl propane sulfonic acid and their
derivatives.
21. The method of claim 5, wherein the chain-transfer agents are
selected from the group consisting of: thiols, formic acid and
alkali metal formates.
22. The method of claim 5 wherein the oxygen scavengers are
selected from the group consisting of: sodium sulfite, sodium
bisulfite, sodium thiosulfate, sodium lignosulfate, ammonium
bisulfite, hydroquinone, diethylhydroxyethanol,
diethylhydroxylamine, methylethylketoxime, ascorbic acid,
erythorbic acid, and sodium erythorbate.
23. The method of claim 5 wherein the pH adjusters are selected
from the group consisting of: sodium hydroxide and potassium
hydroxide.
24. The method of claim 5 where the gel strength modifiers comprise
clays, and more preferably comprise clays selected from the group
consisting of: diatomite, bentonite, lignocellulose, bentonite,
montmorillonite, kaolinoite, and mixtures thereof.
25. A method of using mechanical or physical processes to grind
controlled particle gel to sizes ranging from about 0.1 micron to
500 micron in diameter for the purpose of conformance control in
oil and gas production.
26. The method of claim 25 wherein the mechanical processes are
selected from: fluid energy or jet mills, stirred media mills, ball
mills, colloid mills, vibrating mills, rotor mills, cutting mills,
disc mills, jaw crushers, and mortar grinders, to grind particle
gels to desirable particle sizes.
27. The method of claim 25 wherein processes can be performed under
dry or wet conditions.
28. The method of claim 25 wherein said process can be repeated in
multiple circulations, until the desirable particle size is
achieved.
29. The method of claim 25 wherein the physical processes further
comprises spray drying.
Description
RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/780,950, filed on Feb. 28, 2006, which is hereby
incorporated by reference in its entirety as fully set herein.
FIELD OF THE INVENTION
[0002] The present invention relates to the field of hydrocarbon
production. Particularly, the present invention relates to the
manufacture of particles with improved physical and chemical
characteristics that when added to injection water will further
improve the crude hydrocarbon recovery from subterranean
heterogeneous reservoirs.
BACKGROUND OF THE INVENTION
[0003] Many reservoirs from which oil and gas are produced are not
homogeneous in their geologic properties (e.g. porosity and
permeability). In fact, for many of such reservoirs, the
differences in the permeability (ability to allow fluid flow) among
the different geologic layers can vary as much as several orders of
magnitude.
[0004] Commonly a fluid, particularly water, is injected into an
injection well completed into an oil reservoir. The injected water
will mobilize and push some of the oil in place to a nearby
production well where the oil and injected fluid are co-produced. A
wide variation in the permeability (a property that measures the
ability to transmit flow) among the geologic layer of rock that
contain oil within its porous spaces in the subsurface reservoir
causes such water injection to be not uniform, with the larger
proportion of the water entering into the higher permeability
geologic layers. This condition results in a very non-uniform
displacement of the oil within the reservoir, with most of the oil
quickly mobilized from high permeability layers and little from the
lower permeability layers. The result is the fluid exiting
production wells will have quickly a high percentage of water and
less and less oil. The displacement process reaches the economic
limit when the level of produced water is too high, and not enough
oil is recovered, at a time when a large volume of oil remains in
the bypassed, and not yet swept, lower permeability regions of the
reservoir.
[0005] FIG. 1 illustrates the common situation of an oil reservoir
having an undesirable distribution of injected water and poor
coverage of target subterranean formations containing crude oil.
FIG. 1 represents a side view of a geologic formation between an
injection and production well. Item 1 represents a stream of
pressurized water being forced into the injection well 2. The well
bore is completed so that there is no opening into non-oil bearing
geologic interval 3. Openings are present in the well bore across
the oil bearing geologic formations 4 and 5. Formation 4 has much
higher permeability than formation 5. In the situation depicted,
the much larger fraction of the injected water 6 enters and exits
the higher permeability formation 4. Little of the injected water 7
enters and exits from Formation 5. This is an undesirable result
because any free oil in the high permeability formation is
recovered quickly, but little of the oil from the lower
permeability formation 5. The result is that the total produced
stream 8 (a mixture of the fluids from both formation 4 and 5)
quickly has a very high percentage of water and little oil that
proceeds up the well bore of the production well 9. This behavior
causes the process of water injection to become uneconomic soon,
and there is still a high crude oil content left behind in the
lower permeability formation 5.
[0006] One approach to improve the oil displacement process is to
provide some means to block, or at least significantly increase the
flow resistance, selectively in these very high permeability
geologic zones, sometimes called "thief zones". If a process is
successful in accomplishing this objective, then the water injected
thereafter is diverted to enter now preferentially other geological
layers of rock with lower permeability. This then forces the water
to displace oil not before contacted significantly by the injection
fluid. Such a process to make the injected fluid, such as water,
sweep the oil reservoir in a more uniform fashion has been called
"conformance control".
[0007] Conformance control processes for an injection well are
applied usually after offset production wells begin to experience a
high fraction of water in the produced fluids. Recently, the
research of injection fluid diversion has developed some chemical
processes in which plugging agents are added to the injection
water. These chemical systems have included bulk gel, sequential
injection for in-situ gel formation, and colloidal dispersion gel
(CDG). Bulk gel refers to adding polymer and a cross-linker to
water and allowing some gel reaction to occur. This fluid is
injected into an injection well for some period of time, followed
by normal water injection. Another variation is to inject slugs of
polymer solution and cross-linking solution separately, and then
having a blocking gel form inside the reservoir as these chemicals
mix together and react in-situ. The CDG process has a low
concentration of polymer and cross-linker added together to the
injection water being agitated at the surface. The process with a
partial gel reaction and mixing at the surface creates fine
particles before injection of this fluid. The concept is that the
chemical components in this fluid will further react and create a
stronger blocking gel in-situ.
[0008] However, these chemical conformance control methods have
significant disadvantages: the bulk gel process described above
requires high concentration of both polymer and cross-linker
chemicals to make a strong gel, and the gelation time and physical
properties are difficult to predict; sequential injection of
polymer and crosslinker solution is questionable regarding
controlling the time to create a gel in-situ and the strength of
the gel that might form; colloidal dispersion gel (CDG) and the
other previous methods described are unstable at more extreme
reservoir conditions and therefore inadequate for reservoirs with
high temperature (greater than 90 degree C.). In addition, the CDG
is not suitable when the salinity exceeds 5000 ppm Total Dissolved
Solids (TDS) and it is not able to block effectively the very high
permeability channels.
[0009] Another, more recent, chemical approach that is gaining
favor because it does not have the above disadvantages is the
so-called Preformed Particle Gel (PPG) technology. The PPG
particles typically are a powder product made up of a cross-linked
polymer that will swell after their addition to a fresh or salt
water. For their application the PPG particles are added to the
injection water for some period of time, and then followed by
normal water injection. These soft, swollen particles dispersed
into an injected brine have the desirable property that as their
suspension is injected, they will block the flow pores of the
target, very high permeability geologic layers in a reservoir that
have little oil remaining. Advantages of the PPG approach versus
the other chemical systems described above include that the PPG
product added has a known chemical composition, and that a PPG
suspension in the injection water created at the surface will have
predictable physical properties. In addition, these PPG suspensions
can be stable and perform their desirable partial plugging action
in the highest permeability zones of the reservoir at harsher
reservoir conditions (up to 120 degree C. and in a brine containing
up 300,000 ppm TDS).
[0010] The PPG technology, however, has two important limitations.
First of all, these PPG particles swell almost immediately when
exposed to water. This means that their desirable selective
plugging action is confined to near the injection well, and thus
these swollen particles are not able to penetrate deeply into the
reservoir. This limits the volume of the reservoir that can be
treated to divert the injection water into the lower permeability
areas that contain high oil content. Secondly, the PPG particles
commercially available have a relatively large size (hundreds of
microns to millimeters in diameter). This limits their application
to plugging only very high permeability (tens of Darcies) layers.
In some cases the problem, highest permeability layer is not so
high, perhaps less than 10 Darcies. In that case it would be
advantageous to have a starting particle of a smaller size, in the
range of tens of microns.
[0011] U.S. Pat. No. 5,662,168 (1997) by Smith discloses the
process involves the use of a water soluble polymer in conjunction
with an aluminum citrate preparation to function as a cross-linker
for the polymer. However, it fails to realize the possible
chromatographic separation in the subterranean formations when
unreacted polymer and this cross linking agent are injected in
separate solutions sequentially. This separation of components can
cause the inefficient cross-linking reaction and only a very weak
gel in-situ.
[0012] Representative preparations of PPG, cross-linked polymeric
particles using various monomers, fillers, cross-linkers and
initiators are described in CN Pat. No. 1,251,856A, 1,552,793A,
1,796,484A, and 1,439,692A. Liu, Y., et al. Paper SPE 99641 (2006)
describes the common particle can only be injected into and move
through those porous media with permeability of about 10 Darcies or
greater. The Bai, et al, paper SPE 89468 (2004) discusses about the
particle gel propagation behaviors through pore throats at both
microscopic and macroscopic scales. Particle gel can move through
porous media only if a driving pressure gradient is larger than a
threshold pressure gradient. The chemistry of the above patents
only describes a single cross-linking agent in the particles,
particles of very large size (as much as millimeters in diameter),
and that the particle gels swell as soon as they are mixed into
water. Hence their applications will be only near the injection
well bore and or for reservoirs with thief zones of very high
permeability zones or fractures.
[0013] U.S. Pat. No. 5,465,792 (1995) and U.S. Pat. No. 5,735,349
(1998) by Dawson et al. (BJ Services) disclose the use of swellable
cross-linked superabsorbent polymeric microparticles for modifying
the permeability of subterranean formation. However, swelling of
the superabsorbent microparticles described therein is induced by
changes of the carrier fluid from hydrocarbon to aqueous or from
water of high salinity to water of low salinity. The patents are
not for preformed gel. All their examples and claims are for water
soluble polymer in an emulsion condition. U.S. Pat. No. 6,454,003B1
(2002), U.S. Pat. No. 6,729,402B2 (2004) and U.S. Pat. No.
6,984,705B2 (2006) by Chang et al. disclose a composition
comprising expandable cross-linked polymeric microparticles to be
used for modifying the permeability of subterranean formations.
Large percentages of surfactant are required for preparation of the
microparticles via emulsification, which increases the product cost
substantially. In addition, there is an additional environmental
issue by including the surfactant, not to mention the added
complexity of working with an emulsion system to make the product.
The unexpanded particle size can only be as large as 10 micron due
to the limitation of the microemulsion system. Such small particle
may get into the low permeability matrix target zones and
inadvertently plug areas rich in residual oil. Again, the system
disclosed in these patents involves microemulsion rather than
preformed gelation. Having a microemulsion will significantly
increase the cost of the treatment product. Moreover, the micron
level particle size makes the product less desirable for treating
very high permeability zones or fractured reservoirs.
[0014] According to the previous references, a need exists for
improving the full potential of performing in-depth conformance
control treatment. For in-depth conformance control, adjustable
initial particle size in non-emulsion solution with low threshold
pressure is favorable. Moreover, none of the references cited
consider an expandable and hydrophilic polymeric particle made in a
non-emulsion system that has controllable size, hardness, and
swelling delay when added to fresh water or a salty brine.
SUMMARY OF THE INVENTION
[0015] The present invention is a controlled particle that has a
preferred size range from 10 micron to 5 millimeters. These
expandable and hydrophilic polymeric particles are made in a
non-emulsion system. Furthermore they have the property of allowing
their swollen state in a fresh or salt water to be delayed to a
specified time under different reservoir condition and to a
controllable extent.
[0016] These particles are prepared from a chemical reaction
involving one or more polymerizable monomers (typically acrylamide
monomer), one or more controlled monomers whose decomposition is
kinetically controllable, one or more stable cross-linkers,
initiators, bases, reducing promoters, regulators, stabilizers,
chelating agents, thermal agents, chain-transfer agents, oxygen
scavengers, pH adjusters, and gel strength modifiers in aqueous
solution. The selection of the reactants, especially the controlled
monomers and their concentration will control the delay time before
the onset of particle swelling and also influence the extent and
physical properties of the swollen particle, when such particles
are added to fresh or salt water.
[0017] Several methods may be employed to reduce the size of the
created particle gel to a desired size. These include, but are not
limited to, mechanical methods (such as fluid energy or jet mills,
stirred media mills, ball mills, colloid mills, vibrating mills,
rotor mills, cutting mills, disc mills, jaw crushers, and mortar
grinders), physical methods (such as spray drying), or chemical
methods (polymerization in suspension). Such practices may reduce
the initial size of these particles to be as small as 0.1 micron in
diameter.
[0018] These gel particles may be especially advantageous when used
as selective plugging agents added to fresh or salt water injected
into an oil reservoir. The features of having a controllable time
delay before significant onset of swelling in water, and their
smaller initial size give them the desirable capability to block
target higher permeability rock layers further from the injection
well than otherwise.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The present invention is to improve on the current particle
and gel technology for selective plugging of high water flow
channels in oil reservoirs. The Controlled Particle Gel (CPG)
composition of the present invention is designed to overcome the
main drawbacks of the in-situ gelation systems, which are lack of
control of the timing and the extent of the gelation and flow
resistance effect due to adsorption, dilution or degradation of the
polymer, pH change. In addition, these chemical systems have
limitations in their lack of stability to high temperature and
salinity. The process disclosed here also is superior to the
current Preformed Particle Gel (PPG) products that have little or
no delay in their swelling behavior and are available only in sizes
of hundreds of microns in diameter or larger. The CPG particles
have the improved property that their delay in swelling time and
extent may be controlled. This enhanced feature is due to the
incorporation of a controlled monomer, which will decompose over a
designed period of time that then triggers the significant
expansion of the particles. Another improvement disclosed in the
present invention is that any particle gel may be reduced in size
to a diameter as small as 0.1 microns by mechanical, physical, or
chemical methods. These improved properties allow such preformed
particle gels to penetrate farther into an oil reservoir.
[0020] The adverse results illustrated in FIG. 1 may be improved by
the injection of a water treatment fluid containing Controlled
Particle Gel (CPG). The suspended particles will enter and plug
preferentially the very high permeability formation 4. In
particular, with CPG particles having their designed delay in
swelling time, and their initial relatively small particle size,
they will penetrate a significant distance from the injection well
2 into the high permeability formation 4. Once in this formation
environment for a designed period of time, the CPG particles will
begin to swell and thereby plug significantly the very high
permeability formation 4. Provided the permeability of the
formation 5 is low enough (substantial contrast in formation
permeability between 4 and 5), the initial size of the CPG
particles may be selected so that they have the desirable outcome
of being large enough not to enter into formation 5, while still
being allowed to penetrate deeply before they swell into the high
permeability formation 4.
[0021] FIG. 2 illustrates the improvement in a water injection
process of an oil reservoir after completing a treatment of
Controlled Particle Gel (CPG). The numbers and their general
meaning are the same as FIG. 1. FIG. 2 represents a side view of a
geologic formation between an injection and production well. Item 1
represents a stream of pressurized water being forced into the
injection well 2. The well bore is completed so that there is no
opening into non-oil bearing geologic interval 3. Openings are
present in the well bore across the oil bearing geologic formations
4 and 5. Formation 4 had much higher permeability than formation 5
originally, but after the CPG treatment, now formation 4 has a much
lower permeability to injection water than previously. This
alteration in the geologic permeability now causes a much smaller
fraction of the injected water 6 to enter and exit the higher
permeability formation 4. Most of the injected water 7 instead
enters and exits from Formation 5. This is a desirable outcome
because now most of the injection water 1 will contact and mobilize
more of the free oil previously untouched. The result is that the
total produced stream 8 (a mixture of the fluids from both
formation 4 and 5) soon will have an improvement with a lower
percentage of water and more oil that proceeds up the well bore of
the production well 9.
[0022] The CPG particles for this invention may be made by reacting
monomers, controlled monomers, stable cross-linkers, initiators,
bases, reducing promoters, regulators, stabilizers, thermal agents,
chain-transfer agents, oxygen scavengers, pH adjusters, gel
strength modifiers, in aqueous solution under non-emulsion
condition In the disclosure of CPG preparation, the term "Monomer"
refers to nonionic monomer, anionic monomer, cationic monomer,
zwitterionic monomer, betaine monomer, and amphoteric ion pair
monomer. Nonionic monomer, anionic monomer, and cationic monomers
are preferred. The representative nonionic monomers include vinyl
amide, acryloylmorpholine, acrylate, maleic anhydride,
N-vinylpyrrolidone, vinyl acetate, N-vinyl formamide and their
derivatives, such as hydroxyethyl (methyl)acrylate
CH2=CR--COO--CH2CH2OH (I) and CH2=CR--CO--N(Z1)(Z2) (2)
N-substituted (methyl)acrylamide (II). R.dbd.H or Me; Z1=5-15C
alkyl; 1-3C alkyl substituted by 1-3 phenyl, phenyl or 6-12C
cycloalkyl (both optionally substituted) and Z2=H; or Z1 and Z2 are
each 3-10C alkyl; (II) is N-tert. hexyl, tert. octyl,
methylundecyl, cyclohexyl, benzyl, diphenylmethyl or triphenyl
acrylamide. The vinyl amide is preferred nonionic monomer. Examples
of vinyl amide include acrylamide, methacrylamide,
N-methylacrylamide, N,N-dimethylacrylamide. The representative
anionic monomers include polymerizable organic acids and their
salts, and quaternary salts. The organic acids are preferred
anionic monomer. Examples of organic acids include acrylic acid,
methacrylic acid, maleic acid, itaconic acid, acrylamido
methylpropane sulfonic acid, vinylphosphonic acid, styrene sulfonic
acid. The representative cationic monomers include quaternary
ammonium or acid salts of vinyl amide, vinyl carboxylic acid,
methacrylate and their derivatives. The quaternary ammonium salt
derivatives from acrylamide or acrylic acid are preferred cationic
monomer.
[0023] The term "Controlled monomer" refers to kinetically
controllable decomposition of monomers, wherein vinyl or allyl
groups are bridged by one or more ethers, esters, azos, and amides,
or other decomposable moieties. Representative controlled monomers
include [CR.sub.1R.sub.2.dbd.CR.sub.3--CO-]n esters of di, tri, or
tetra alcohols (I), [C R.sub.1R.sub.2.dbd.C R.sub.3--O-]n esters of
di, tri, or tetra functional acids (II), [C
R.sub.1R.sub.2.dbd.CR.sub.3--CR.sub.4R.sub.5--O]n esters of di,
tri, or tetra functional acids (III),
[CR.sub.1R.sub.2.dbd.CR.sub.3--CO-]m amides (IV), [C
R.sub.1R.sub.2.dbd.C R.sub.3--].sub.2 of bisazo (V), [C
R.sub.1R.sub.2.dbd.C R.sub.3--CR.sub.4R.sub.5--].sub.2 of bisazo
(VI), and the derivatives of (I)-(VI). R.sub.1.dbd.H or Me,
R.sub.2.dbd.H or Me, R.sub.3.dbd.H or Me, R.sub.4.dbd.R.sub.5.dbd.H
or Me, n=2, 3, or 4, m=2, 3, or 4. Alcohols in (I) include
ethyleneglycol, polyethyleneglycol, ethoxylated trimethylol,
ethoxylated pentaerythritol, and their derivatives. Typical
controlled monomers in class (IV) include N-tert. hexyl, tert.
octyl, methylundecyl, cyclohexyl, benzyl, diphenylmethyl, triphenyl
diacrylamides, diacrylamide, methacrylamide, piperazine
diacrylamide, and their derivatives. Preferred controlled monomers
include water soluble diacrylates and polyfunctional vinyl
derivatives of a polyalcohol. More preferred controlled monomers
include polyethylene glycol diacrylates. The monomers and
controlled monomers may be polymerized and cross-linked in a
non-emulsion aqueous solution.
[0024] The term "Aqueous solution" refers to water, buffer solvent,
or other non-oil and non-surfactant solutions. The preferred
solvent for aqueous solutions is deionized water.
[0025] The term "Stable cross-linker" refers to aluminum salt,
zirconium salt, chromium salt or organic cross-linker. The organic
cross-linkers, such as methylenebisacrylamide,
hexamethylenetetramine, phenol aldehyde, are preferred. The stable
cross-linker is optional according to specific subterranean
conditions.
[0026] The initiators (e.g. ammonium persulfate, potassium
persulfate, sodium persulfate, sodium bromate, sodium bisulfite, or
mixture), optionally with bases (e.g. sodium carbonate, sodium
bicarbonate, sodium hydroxide), reducing promoters (e.g. potassium
metabisulfite, sodium sulfite, thionyl chloride, thionyl bromide),
regulators (e.g. alcohols), stabilizers (e.g. phenol,
m-dihydroxybenzene, hydroquinone), chelating agents (e.g. ethylene
diamine tetra acetate), thermal agents (e.g. 2-acrylamido-2-methyl
propane sulfonic acid), chain-transfer agents (e.g. thiols, formic
acid and alkali metal formates such as sodium formate), oxygen
scavengers (e.g. sodium sulfite, sodium bisulfite, sodium
thiosulfate, sodium lignosulfate, ammonium bisulfite, hydroquinone,
diethylhydroxyethanol, diethylhydroxylamine, methylethylketoxime,
ascorbic acid, erythorbic acid, and sodium erythorbate), pH
adjusters (e.g. sodium or potassium hydroxide), and gel strength
modifiers (e.g. bentonite, lignocellulose, clay, montnorillonite,
diatomite, kaolinoite, other fillers, or mixture), are employed to
initiate the polymerization reaction.
[0027] In preparing the starting reaction mixture, the compounds to
be polymerized are dissolved within an aqueous solution. The amount
of aqueous solution, such as deionized water, may vary, but
typically from 15 to 70% of the total weight of the initial
reaction solution. The amount of monomers may vary, but typically
are from 5 to 60% of the total weight of start reacting solution.
The amount of controlled monomers may vary, but typically is from
0.01 to 30% of the total weight of the initial.reactinon solution.
Depending upon the amount of total monomers, the stable
cross-linker is typically from 0 to 5%, and the gel strength
modifier is typically from 0 to 60%. The caustic component is
optional to hydrolyze certain monomers, such as acrylamide, and its
amount of use may vary, but typically from 0 to 10%. The pH
adjusters may be necessary. The typical pH range of reacting
solution is 6.5 to 11. The reducing promoters, regulators,
stabilizers, chelating agent, thermal agent, chain-transfer agent,
oxygen scavenger are optional according to the specific injection
water and subterranean formation, and their amounts of use may
vary. The order of addition for the reactants may vary; the typical
order is the least polar compound first to ensure it can be
dissolved completely, then followed by more polar compounds.
[0028] After the initial reaction mixture is agitated, at an
ambient temperature, typically from 15 to 30 degree C., the
initiator or initiators mixture is then slowly added into the
dynamically mixed, sheared or oscillated reacting solution to
achieve a homogenized reacting condition. The amount of initiator
may vary according to the monomers concentration, but typically
from 0.01% to 0.2%. Because of the exothermic nature of the
reaction initiated by the addition of the initiators, evidence of
the reaction is inferred by an increased temperature. Preferably
the reaction is kept at the initial temperature by means of having
the reactor jacketed with a cooling fluid, or having the reactor
surrounded by a vessel containing a circulating fluid. A gradual
increase of the temperature of the reacting system is also
acceptable. The result of the reaction process will result in a
fine gel ready for the post-treatment. The polymerizing and
cross-linking reaction are preferably carried out in oxygen free or
in a reduced oxygen environment. However, short exposure to air is
also acceptable.
[0029] The reaction can be performed in either a batch process or
continuous process. Due to the fast polymerization reaction,
typically several minutes, the continuous process is preferred for
medium to large scale production. The deoxygenated monomers and
supplemental materials are continuously pumped to a reaction
vessel, and the reacted gel is continuously transferred away from
the vessel. The gel is squeezed through small holes and cut to
small particles or lumps for stepwise baking, breaking, sieving
post-treatments. The baking temperature may vary according to the
specific formulation, but the typical baking temperature is 15 to
20 degree C. lower than the decomposing temperature of controlled
monomers used in the formulation.
[0030] For small to medium scale production, the batch process is
also preferred. The initial reacting solution, mixed monomers and
supplemental materials, is deoxygenated with inert gas, such as
nitrogen, for about 30 to 50 minutes. Polymerization is initiated
at room temperature. The temperature typically rises to about 60
degree C. or higher by the heat released during polymerization. The
polymerized mixture is typically kept at that higher temperature,
usually from 65 to 80 degree C. to complete the reaction, resulting
in production of soft gel lumps. The gel lumps are dried on trays
in an oven, and then are ground to desirable sizes.
[0031] The size reduction of resulting polymeric gel particles can
be achieved by mechanical methods (e.g. fluid energy or jet mills,
stirred media mills, ball mills, colloid mills, vibrating mills,
rotor mills, cutting mills, disc mills, jaw crushers, and mortar
grinders), physical methods (e.g. spry drying) or chemical methods
(e.g. polymerization in suspension). The mechanical grinding
approaches by jet mill, ball mill and colloid mill are preferred.
The reported data indicates that industrial scale ball mill can
grind hard, brittle materials under 1 micron in size (e.g.
Planetary ball mill by Retsch). The in-house test described in an
example in this application shows the dry gel particle after being
ground in a laboratory scale ball mill jar, can pass through a 400
mesh sieve, an opening of less than 37 micron diameter. An
industrial scale colloid mill can grind colloid particles down to 1
micron in diameter, and an in-house test shows the gel particle
suspension, after grinding in a laboratory colloid mill, can pass
200 mesh sieve, less than 74 micron diameter, under 20 psi positive
pressure.
[0032] Due to the characteristics of the size of initial particle,
its hydrophilic nature, and that it contains controlled monomer
that will decompose to allow the particle to swell in a predictable
manner, the composition of this invention can propagate far into
the reservoir.
[0033] In a preferred aspect of this embodiment, this CPG
composition is added to injection water as part of a secondary
water recovery process, tertiary carbon dioxide injection,
chemical, or air injection for recovery of hydrocarbon from
subterranean sandstone or carbonate formation. This will provide
controlling the near well-bore and in-depth formation conformance
vertically and laterally by selectively blocking the high water
channels. The composition can be added in an amount from about 50
to 20,000 ppm, preferably from about 500 to 5000 ppm and more
preferably from about 1000 to 3000 ppm based on solid content, with
produced water, sea water, or fresh water.
[0034] The forgoing may be better understood by reference to the
following examples, which are presented for purposes of
illustration and are not intended to limit the scope of this
invention.
EXAMPLES
Example 1
Preparation of Sample 27
[0035] In the present example, a single aqueous phase was prepared
by adding 8.25 g acrylamide, 21.75 g sodium salt of
2-acrylamido-2-methylpropane sulfonic acid, 0.386 g polyethylene
glycol 200 diacrylate, and 0.0004 g methylene bisacrylamide to 30.6
g deionized water with then mixing. At an ambient temperature of
15-30.degree. C., an initiator mixture of 400 .mu.l 5% sodium
bromate and 400 .mu.l 5% sodium bisulfite was added slowly to the
solution with strong mixing. Within about 5 minutes, the reaction
of polymerization took place with heat released, resulting in a
fine gel.
Example 2
Preparation of Sample 31
[0036] In this example, the procedure of example 1 was repeated
except that 6.10 g polyethylene glycol 200 diacrylate and no
methylene bisacrylamide were added to the formula. All other
components and reaction conditions remained the same.
Example 3
[0037] Comparison of swelling behavior of Sample 27 versus Sample
31 demonstrates the controllability the swell time and extent with
our composition.
[0038] Sample 27 and Sample 31 suspensions were both prepared at a
concentration of 1 wt % in distilled water and had the pH adjusted
to be between 8 to 9. A portion of each suspension was aged at 40
degree C. and at 60 degree C. for 2 days. The results are shown
below:
TABLE-US-00001 Temperature (Centigrade) Sample 27 Sample 31 40
fluid fluid 60 stiff gel fluid
[0039] These results demonstrate that the composition of the Sample
27 is suitable for an application where the controlled monomer is
designed to decompose within 2 days at 60 degree C. Furthermore,
the fact that the Sample 27 remains in a fluid state over the same
aging time at 40 degree C. indicate that for Sample 27 the
mechanism for the loss of effectiveness of the controlled monomer,
thereby causing particle expansion and a gel to form is related to
its exposure to a greater extreme in temperature to 60 degree C.
And Sample 31 is suitable when a longer time delay before
significant particle expansion and gelation is desirable.
Example 4
[0040] Grinding of Sample 27 can reduce size so that it may have a
small diameter and thereby pass through smaller pore holes.
[0041] Sample 27 particles (described in Example 1 and Example 3)
were added to a 0.3 wt % NaCl solution at a concentration of 1000
ppm. This particulate suspension was added to a pressure vessel. A
nitrogen gas line was connected to the top of the pressure vessel
and the gas pressure was adjusted to 20 psi. A valve at the bottom
of the vessel was opened and the fluid exited and passed through a
200.times.200 mesh metal screen mounted in a sealed holder. After
injection of approximately 100 ml of the particle suspension, the
screen was inspected and found to have a significant coating of the
particle gel on the entire surface.
[0042] Next a portion of this same Sample 27 suspension initially
made to a concentration of 1000 ppm in a 0.3 wt % NaCl brine was
added to a laboratory colloidal mill and exposed to 60 minutes of
grinding time. This suspension of particles after grinding also
were passed through a clean 200.times.200 mesh screen under 20 psi
of driving gas pressure. In this case the screen has a much cleaner
appearance with only slight evidence of any solids accumulation in
or on the metal screen.
[0043] This example illustrates it is possible to reduce the size
of these particles significantly by grinding. Because the hole size
in a 200.times.200 mesh screen is about 75 microns in size, this
demonstrates it is possible to grind these particles to a size less
than 75 microns. Based on a rule of thumb that particles must have
a diameter less than one-third the hole size to pass thoroughly
successfully, it is estimated that the 60 minutes of grinding
reduced the average particle size to about 25 microns in diameter.
The ground particles maintain the same composition and have the
same delayed swelling behavior as for the original particles.
Example 5
[0044] The particles created are strongly hydrophilic and will
remain primarily in the water phase.
[0045] The Sample 27 particles described in Example 1 were added as
a 0.5 wt % suspension into a distilled water solution of 80
milliliters volume. Next, this 80 milliliters of particle
suspension fluid was poured into a glass separatory funnel,
followed by 80 milliliters of n-decane. The funnel was shaken by
hand vigorously for 5 minutes, and then left standing for overnight
to allow separation of the aqueous and hydrocarbon phases. Next,
the bottom aqueous layer was drained off from the separatory funnel
into a wide dish. This pre-weighed dish was heated until all of the
liquid has evaporated. After cooling, the dish was re-weighed to
determine the mass of solid particles remaining in the aqueous
phase taken from the separatory funnel. By this method, over 95% of
the initial mass of the particles from Sample 27 remained in the
aqueous phase. This is an insignificant decrease, and is nearly the
same mass of particles as the starting amount. These results
confirm that the suspended particles are hydrophilic in nature and
have a much stronger affinity for the aqueous phase than a
hydrocarbon phase.
Cited Patents
[0046] CN Pat. No. 1,251,856A May 2000 Liu et al. [0047] CN Pat.
No. 1,552,793A December 2004 Wu [0048] CN Pat. No. 1,796,484A July
2006 Li [0049] CN Pat. No. 1,439,692A September 2003 Li et al.
[0050] U.S. Pat. No. 5,662,168 September 1997 Smith [0051] U.S.
Pat. No. 5,465,792 November 1995 Dawson et al. [0052] U.S. Pat. No.
5,735,349 April 1998 Dawson et al. [0053] U.S. Pat. No. 6,454,003B1
September 2002 Chang et al. [0054] U.S. Pat. No. 6,729,402B2 May
2004 Chang et al. [0055] U.S. Pat. No. 6,984,705B2 January 2006
Chang et al.
Other Literature Cited
[0055] [0056] Liu, Y., et al,"Application and Development of
Chemical-Based Conformance Control Treatments in China Oilfields,"
paper SPE 99641 presented at the 2006 SPE/DOE Symposium on Improved
Oil Recovery held in Tulsa, Oklahoma, U.S.A. Apr. 22-26, 2006.
[0057] Bai, B., et al, "Preformed Particle Gel for Conformance
Control: Transport through Porous Media and IOR Mechanisms," paper
SPE 89468 presented at the 2004 SPE/DOE Fourteenth Symposium on
Improved Oil Recovery held in Tulsa, Oklahoma, U.S.A., Apr. 17-21,
2004.
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