TITLE
"COMPOSITIONS AND METHODS FOR DIVERTING INJECTED FLWDS TO
ACfflEVE IMPROVED HYDROCARBON FLUID RECOVERY"
BACKGROUND
[0001] In the first stage of hydrocarbon recovery the sources of energy present in the
reservoir are allowed to move the oil, gas, condensate etc. to the producing wells(s) where they
can flow or be pumped to the surface handling facility. A relatively small proportion of the
hydrocarbon in place can usually be recovered by this means. The most widely used solution to
the problem of maintaining the energy in the reservoir and ensuring that hydrocarbon is driven to
the producing well(s) is to inject fluids down adjacent wells. This is commonly known as
secondary recovery.
[0002] The fluids normally used are water (such as aquifer water, river water, sea water,
or produced water), or gas (such as produced gas, carbon dioxide, flue gas and various others). If
the fluid encourages movement of normally immobile residual oil or other hydrocarbon, the
process is commonly termed tertiary recovery.
[0003] A very prevalent problem with secondary and tertiary recovery projects relates to
the heterogeneity of the reservoir rock strata. The mobility of the injected fluid is commonly
different from the hydrocarbon and when it is more mobile various mobility control processes
have been used to make the sweep of the reservoir more uniform and the consequent
hydrocarbon recovery more efficient. Such processes have limited value when high permeability
zones, commonly called thief zones or streaks, exist within the reservoir rock. The injected fluid
has a low resistance route from the injection to the production well. In such cases the injected
fluid does not effectively sweep the hydrocarbon fluids from adjacent, lower permeability zones.
When the produced fluid is re-used this can lead to fluid cycling through the thief zone to little
benefit and at great cost in terms of fuel and maintenance of the pumping system.
[0004] Numerous physical and chemical methods have been used to divert injected fluids
out of thief zones in or near production and injection wells. When the treatment is applied to a
producing well it is usually termed a water (or gas etc.) shut-off treatment. When it is applied to
an injection well it is termed a profile control or conformance control treatment.
[0005] In cases where the thief zone(s) are isolated from the lower permeability adjacent
zones and when the completion in the well forms a good seal with the barrier (such as a shale
layer or "stringer") causing the isolation, mechanical seals or "plugs" can be set in the well to
block the entrance of the injected fluid. If the fluid enters or leaves the formation from the
bottom of the well, cement can also be used to fill up the well bore to above the zone of ingress.
1
[0006] When the completion of the well allows the injected fluid to enter both the thief
and the adjacent zones, such as when a casing is cemented against the producing zone and the
cement job is poorly accomplished, a cement squeeze is often a suitable means of isolating the
watered out zone.
[0007] Certain cases are not amenable to such methods by virtue of the facts that
communication exists between layers of the reservoir rock outside the reach of cement. Typical
examples of this are when fractures or rubble zones or washed out caverns exist behind the
casing. In such instances chemical gels, capable of moving through pores in reservoir rock have
been applied to seal off the swept out zones.
[0008] When such methods fail the only alternatives remaining are to produce the well
with poor recovery rate, sidetrack the well away from die prematurely swept zone, or abandon
the well. Occasionally the producing well is converted to a fluid injector to increase the field
injection rate above the net hydrocarbon extraction rate and increase the pressure in the reservoir.
This can lead to improved overall recovery but it is worthy of note that the injected fluid will
mostly enter the thief zone at the new injector and is likely to cause similar problems in nearby
wells. All of these are expensive options.
[0009] Near wellbore conformance control methods always fail when the thief zone is in
widespread contact with the adjacent, hydrocarbon containing, lower permeability zones. The
reason for this is that the injected fluids can bypass the treatment and re-enter the thief zone
having only contacted a very small proportion, or even none of the remaining hydrocarbon. It is
commonly known amongst those skilled in the art, that such near wellbore treatments do not
succeed in significantly improving recovery in reservoirs having crossflow of the injected fluids
between zones.
[0010] A few processes have been developed with the aim of reducing the permeability in
a substantial proportion of the thief zone and, or at a significant distance from the injection and
production wells. One example of this is the Deep Diverting Gel process patented by Morgan et
al (1). This has been used in the field and suffered from sensitivity to unavoidable variations in
quality of the reagents which resulted in poor propagation. The gelant mixture is a two
component formulation and it is believed that this contributed to poor propagation of the
treatment into the formation.
[0011] The use of swellable cross linked superabsorbent polymer microparticles for
modifying the permeability of subterranean formations is disclosed in U.S. Pat. Nos. 5,465,792
and 5,735,349. However, swelling of the superabsorbent microparticles described therein is
2
induced by changes of the carrier fluid from hydrocarbon to aqueous or from water of high
salinity to water of low salinity.
[0012] Cross linked, expandable polymeric microparticles and their use for modifying the
permeability of subterranean formations and increasing the mobilization and/or recovery rate of
hydrocarbon fluids present in the formation are disclosed in U.S. Patent Nos. 6,454,003 Bl;
6,709,402 B2; 6,984,705 B2 and 7,300,973 B2 and in published U.S. Patent Application No.
2007/0204989 Al.
SUMMARY
[0013] We have discovered novel polymeric microparticles in which the microparticle
conformation is constrained by hydrolytically labile silyl ether or silyl ester crosslinkers. The
microparticle properties, such as particle size distribution and density, of the constrained
microparticle are designed to allow efficient propagation through the pore structure of
hydrocarbon reservoir matrix rock, such as sandstone. On heating to reservoir temperature
and/or at a predetermined pH, the reversible (labile) internal cross links start to break allowing
the particle to expand by absorbing the injection fluid (normally water).
[0014] The ability of the particle to expand from its original size (at the point of
injection) depends only on the presence of conditions that induce the breaking of the silyl ether or
silyl ester crosslinkers and other labile crosslinkers present in the microparticles. The particles of
this invention can propagate through the porous structure of the reservoir without using a
designated fluid or fluid with salinity higher than the reservoir fluid.
[0015] The expanded particle is engineered to have a particle size distribution and
physical characteristics, for example, particle rheology, which allow it to impede the flow of
injected fluid in the pore structure. In doing so it is capable of diverting chase fluid into less
thoroughly swept zones of the reservoir.
[0016] The rheology and expanded particle size of the particle can be designed to suit the
reservoir target, for example by suitable selection of the backbone monomers or comonomer ratio
of the polymer, or the degree of reversible (labile) and irreversible cross linking introduced
during manufacture.
[0017] In an embodiment, this invention is a composition comprising highly cross linked
expandable polymeric microparticles having unexpanded volume average particle size diameters
of about 0.05 to about 5,000 microns and a cross linking agent content of from 0 to about 300
ppm of non-labile cross linking agent and from about 100 to about 200,000 ppm of labile
3
crosslinking agent, wherein said labile crosslinking agent comprises one or more hydrolytically
labile silyl ether or silyl ester crosslinkers, or a mixture thereof.
[0018] In alternative embodiments, methods for using the above compositions are also
provided.
[0019] Additional features and advantages are described herein, and will be apparent
from the following Detailed Description.
DETAILED DESCRIPTION
[0020] "Acryloxy" means a group of formula CH2=CHC(0)0-. "Methacryloxy" means a
group of formula CH2=C(CH3)C(0)0-.
[0021] "Alkoxy" or "alkoxyl" mean an alkyl group, as defined herein, attached to the
parent molecular moiety through an oxygen atom. Representative alkoxy groups include
methoxyl, ethoxyl, propoxyl, butoxyl, and the like. »
[0022] "Alkyl" means a substituted and unsubstitued groups derived from a straight or
branched chain saturated hydrocarbon by the removal of a single hydrogen atom. Alkyl groups
are exemplified by methyl, ethyl, n- and iso-propyl,«-, sec-, iso- and rert-butyl, and the like.
[0023] "Allyl" means a group of formula -CH2CH=CH2. "Allyloxy" means a group of
formula -OCH2CH=CH2.
[0024] "Amphoteric polymeric microparticle" means a cross linked polymeric
microparticle containing both cationic substituents and anionic substitutents, although not
necessarily in the same stoichiometric proportions. Representative amphoteric polymeric
microparticles include terpolymers of nonionic monomers, anionic monomers and cationic
monomers as defined herein. In an embodiment, the amphoteric polymeric microparticles have a
higher than 1:1 anionic monomer/cationic monomer mole ratio.
[0025] "Ampholytic ion pair monomer" means the acid-base salt of basic, nitrogen
containing monomers such as dimethylaminoethylacrylate (DMAEA), dimethylaminoethyl
methacrylate (DMAEM), 2-methacryloyloxyemyldiemylarnine, and the like and acidic
monomers such as acrylic acid and sulfonic acids such as 2-acrylamido-2-methylpropane
sulfonic acid, 2-methacryloyloxyethane sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid,
and the like.
[0026] "Anionic monomer" means a monomer as defined herein which possesses an
acidic functional group and the base addition salts thereof. Representative anionic monomers
include acrylic acid, methacrylic acid, maleic acid, itaconic acid, 2-propenoic acid, 2-methyl-2-
propenoic acid, 2-acrylamido-2-methyl propane sulfonic acid, sulfopropyl acrylic acid and other
4
water-soluble forms of these or other polymerizable carboxylic or sulphonic acids,
sulphomethylated acrylamide, allyl sulphonic acid, vinyl sulphonic acid, the quaternary salts of
acrylic acid and methacrylic acid such as ammonium acrylate and ammonium methacrylate, and
the like. In an embodiment, anionic monomers include 2-acrylamido-2-methyl propanesulfonic
acid sodium salt, vinyl sulfonic acid sodium salt and styrene sulfonic acid sodium salt. In an
embodiment, the anionic monomer is 2-Acrylamido-2-methyl propanesulfonic acid sodium salt.
[0027] "Anionic polymeric microparticle" means a cross linked polymeric microparticle
containing a net negative charge. Representative anionic polymeric microparticles include
copolymers of acrylamide and 2-acrylamido-2-methyl propane sulfonic acid, copolymers of
acrylamide and sodium acrylate, terpolymers of acrylamide, 2-acrylamido-2-methyl propane
sulfonic acid and sodium acrylate and homopolymers of 2-acrylamido-2-methyl propane sulfonic
acid. In an embodiment, the anionic polymeric microparticles are prepared from about 95 to
about 10 mole percent of nonionic monomers and from about 5 to about 90 mole percent anionic
monomers. In an embodiment, the anionic polymeric microparticles are prepared from about 95
to about 10 mole percent acrylamide and from about 5 to about 90 mole percent 2-acrylamido-2-
methyl propane sulfonic acid.
[0028] "Aryl" means substituted and unsubstituted aromatic carbocyclic radicals and
substituted and unsubstituted heterocyclic aromatic radicals including, but not limited to, phenyl,
1-naphthyl or 2-naphthyl, fluorenyl, pyridyl, quinolyl, thienyl, thiazolyl, pyrimidyl, indolyl, and
the like.
[0029] "Arylalkyl" refers to an aryl group as defined herein, attached to the parent
molecular moiety through an alkylene group. Representative arylalkyl groups include
phenylmethyl, phenylethyl, phenylpropyl, 1-naphthylmethyl, and the like.
[0030] "Betaine-containing polymeric microparticle" means a cross linked polymeric
microparticle prepared by polymerizing a betaine monomer and one or more nonionic monomers.
[0031] "Betaine monomer" means a monomer containing cationically and anionically
charged functionality in equal proportions, such that the monomer is net neutral overall.
Representative betaine monomers include N,N-dimethyI-N-acryloyloxyethyl-N-(3-sulfopropyl)-
ammonium betaine, N,N-dhnethyl-N-methacryloyloxyethyl-N-(3 -sulfopropyl)-ammonium
betaine, N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyI)-ammonium betaine, N,Ndimethyl-
N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine, N,N-dimethyl-Nacryloxyethyl-
N-(3-sulfopropyl)-ammonium betaine, N,N-dimethyl-N-acrylamidopropyl-N-(2-
carboxymethyl)-ammonium betaine, N-3-sulfopropylvinylpyridine ammonium betaine, 2-
(methylthio)ethyl methacryloyl-S-(sulfopropyl)-sulfonium betaine, l-(3-sulfopropyl)-2-
5
vinylpyridinium betaine, N-(4-suIfobutyl)-N-methyldiaUylamine ammonium betaine (MDABS),
N,N-diallyl-N-methyl-N-(2-sulfoethyl) ammonium betaine, and the like. In an embodiment, the
betaine monomer is N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl)-ammonium
betaine.
[0032] "Cationic Monomer" means a monomer unit as defined herein which possesses a
net positive charge. Representative cationic monomers include the quaternary or acid salts of
dialkylaminoalkyl acrylates and methacrylates such as dimethylaminoethylacrylate methyl
chloride quaternary salt (DMAEAMCQ), dimethylaminoethylmethacrylate methyl chloride
quaternary salt (DMAEMMCQ), dimethylaminoethylacrylate hydrochloric acid salt,
dimethylaminoethylacrylate sulfuric acid salt, dimethylaminoethyl acrylate benzyl chloride
quaternary salt (DMAEABCQ) and dimethylaminoethylacrylate methyl sulfate quaternary salt;
the quaternary or acid salts of dialkylaminoalkylacrylamides and methacrylamides such as
dimethylaminopropyl acrylamide hydrochloric acid salt, dimethylaminopropyl acrylamide
sulfuric acid salt, dimethylaminopropyl methacrylamide hydrochloric acid salt and
dimethylaminopropyl methacrylamide sulfuric acid salt, methacrylamidopropyl trimethyl
ammonium chloride and acrylamidopropyl trimethyl ammonium chloride; and N,N-diallyldialkyl
ammonium halides such as diallyldimethyl ammonium chloride (DADMAC). In an
embodiment, cationic monomers include dimethylaminoethylacrylate methyl chloride quaternary
salt, dimethylaminoethylmethacrylate methyl chloride quaternary salt and diallyldimethyl
ammonium chloride. In an embodiment, the cationic monomer is diallyldimethyl ammonium
chloride.
[0033] "Cross linking monomer" means an ethylenically unsaturated monomer
containing at least two sites of ethylenic unsaturation which is added to constrain the
microparticle conformation of the polymeric microparticles of this invention. The level of cross
linking used in these polymer microparticles is selected to maintain a rigid non-expandable
microparticle configuration. Cross linking monomers according to this invention include both
labile cross linking monomers and non-labile cross linking monomers.
[0034] "Emulsion," "microemulsion," and "inverse emulsion" mean a water-in-oil
polymer emulsion comprising a polymeric microparticle according to this invention in the
aqueous phase, a hydrocarbon oil for the oil phase and one or more water-in-oil emulsifying
agents. Emulsion polymers are hydrocarbon continuous with the water-soluble polymers
dispersed within the hydrocarbon matrix. The emulsion polymer are optionally "inverted" or
converted into water-continuous form using shear, dilution, and, generally an inverting
6
surfactant. See, U.S. Pat. No. 3,734,873, the entire content of which is incorporated herein by
reference.
[0035] "Fluid mobility" means a ratio that defines how readily a fluid moves through a
porous medium. This ratio is known as the mobility and is expressed as the ratio of the
permeability of the porous medium to the viscosity for a given fluid.
1. X- — for a single fluid x flowing in a porous medium.
77,
[0036] When more than one fluid is flowing the end point relative permeabilities must be
substituted for the absolute permeability used in equation 1.
1Crr
2. h. = — for a fluid x flowing in a porous medium in the presence of one or more
other fluids.
[0037] When two or more fluids are flowing the fluid mobilities may be used to define a
Mobility ratio.
3. M= —= ^
Ay TfxKry
[0038] The mobility ratio is of use in the study of fluid displacement, for example in
water flooding of an oil reservoir where x is water and y is oil, because the efficiency of the
displacement process can be related to it. As a general principle at a mobility ratio of 1 the fluid
front moves almost in a "plug flow" manner and the sweep of the reservoir is good. When the
mobility of the water is ten times greater than the oil viscous instabilities, known as fingering,
develop and the sweep of the reservoir is poor. When the mobility of the oil is ten times greater
than the water the sweep of the reservoir is almost total.
[0039] "Hydrolytically labile silyl ether or silyl ester crosslinkers" means a cross-linking
monomer as defined above which further comprises at least one -Si-O- group or at least one -
Si-O(CO) - group, or a mixture thereof and at least two vinyl, vinyloxy, aliyoxy, acryloxy,
methacryloxy or allyl groups, or a mixture thereof.
[0040] "Ion-pair polymeric microparticle" means a cross linked polymeric microparticle
prepared by polymerizing an ampholytic ion pair monomer and one more anionic or nonionic
monomers.
[0041] "Labile cross linking monomer" means a cross linking monomer which can be
degraded by certain conditions of heat and/or pH, after it has been incorporated into the polymer
structure, to reduce the degree of crosslinking in the polymeric microparticle of this invention.
The aforementioned conditions are such that they can cleave bonds in the "cross linking
monomer" without substantially degrading the rest of the polymer backbone. Representative
labile cross linking monomers include diacrylamides and methacrylamides of diamines such as
the diacrylamide of piperazine, acrylate or methacrylate esters of di, tri, tetra hydroxy compounds
including ethyleneglycol diacrylate, polyethyleneglycol diacrylate, trimethylopropane
trimethacrylate, ethoxylated trimethylol triacrylate, ethoxylated pentaerythritol tetracrylate, and
the like; divinyl or diallyl compounds separated by an azo such as the diallylamide of 2,2'-
Azobis(isbutyric acid) and the vinyl or allyl esters of di or tri functional acids. In an
embodiment, labile cross linking monomers include water soluble diacrylates such as PEG 200
diacrylate and PEG 400 diacrylate and polyfunctional vinyl derivatives of a polyalcohol such as
ethoxylated (9-20) trimethylol triacrylate.
[0042] "Monomer" means a polymerizable allylic, vinylic or acrylic compound. The
monomer may be anionic, cationic, nonionic or zwitterionic. In an embodiment, monomers
comprise vinyl monomers. In another embodiment, monomers comprise acrylic monomers.
[0043] "Nonionic monomer" means a monomer as defined herein which is electrically
neutral. Representative nonionic monomers include N-isopropylacrylamide, N,Ndimethylacrylamide,
N,N-diethylacrylamide, dimethylaminopropyl acrylamide,
dimethylaminopropyl methacrylamide, acryloyl morpholine, hydroxyethyl acrylate,
hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate,
dimethylaminoethylacrylate (DMAEA), dimemylaminoethyl methacrylate (DMAEM), maleic
anhydride, N-vinyl pyrrolidone, vinyl acetate and N-vinyl formamide. In an embodiment,
nonionic monomers include acrylamide, N-methylacrylamide, N,N-dimethylacrylamide and
methacrylamide. In another embodiment, the nonionic monomer is acrylamide.
[0044] "Non-labile cross linking monomer" means a cross linking monomer which is not
degraded under the conditions of temperature and/or pH which would cause incorporated labile
cross linking monomers and incorporated hydrolytically labile silyl ether ether or silyl ester
crosslinking monomers to disintegrate. Non-labile cross linking monomer is added, in addition
to the labile cross linking monomer, to control the expanded conformation of the polymeric
microparticle. Representative non-labile cross linking monomers include methylene
bisacrylamide, diallylamine, triallylamine, divinyl sulfone, diethyleneglycol diallyl ether, and the
like. In an embodiment, the non-labile cross linking monomer is methylene bisacrylamide.
8
[0045] "Vinyl" means a group of formula -CH=CH2. "Vinyloxy" means a group of
formula -OCH=CH2.
[0046] Highly cross linked expandable polymeric microparticles suitable for use in the
composition and method of this invention are prepared by polymerizing monomers in the
presence of hydrolytically labile silyl ether or silyl ester crosslinkers and optional labile
crosslinkers and non-labile crosslinkers.
[0047] In an embodiment, the hydrolytically labile silyl ether or silyl ester crosslinkers
and any labile crosslinkers are present in a combined amount of about 100 to about 200,000 ppm,
based on total weight of monomer. In another embodiment, the silyl ether or silyl ester
crosslinkers and any labile crosslinkers are present in a combined amount from about 1,000 to
about 200,000 ppm. In another embodiment, the silyl ether or silyl ester crosslinkers and any
labile crosslinkers are present in a combined amount from about 9,000 to about 200,000 ppm. In
another embodiment, the silyl ether or silyl ester crosslinkers and any labile crosslinkers are
present in a combined amount from about 9,000 to about 100,000 ppm. In another embodiment,
the silyl ether or silyl ester crosslinkers and any labile crosslinkers are present in a combined
amount from about 20,000 to about 60,000 ppm. In another embodiment, the silyl ether or silyl
ester crosslinkers and any labile crosslinkers are present in a combined amount from about 500 to
about 50,000 ppm. In another embodiment, the hydrolytically labile silyl ether or silyl ester
crosslinkers and any labile crosslinkers are present in a combined amount of about 1,000 to about
20,000 ppm.
[0048] In an embodiment, the non-labile cross linker is present in an amount from about
0 to about 300 ppm, based on total weight of monomer. In another embodiment, the non-labile
cross linker is present in an amount from about 0 to about 200 ppm. In another embodiment, the
non-labile cross linker is present in an amount from about 0 to about 100 ppm. In another
embodiment, the non-labile cross linker is present in an amount of from about 5 to about 300
ppm. In another embodiment, the non-labile cross linker is present in an amount of from about 2
to about 300 ppm. In another embodiment, the non-labile cross linker is present in an amount of
from about 0.1 to about 300 ppm. In the absence of a non-labile cross linker, the polymer
particle, upon complete scission of labile cross linker, is converted into a mixture of linear
polymer strands. The particle dispersion is thereby changed into a polymer solution. This
polymer solution, due to its viscosity, changes the mobility of the fluid in a porous medium. In
the presence of a small amount of non-labile cross linker, the conversion from particles to linear
molecules is incomplete. The particles become a loosely linked network but retain certain
9
'structure.' Such 'structured' particles can block the pore throats of porous media and create a
blockage of flow.
[0049] In an aspect of the present disclosure, the polymeric microparticles of this
disclosure are prepared using an inverse emulsion or microemulsion process to assure certain
particle size range. In an embodiment, the unexpanded volume average particle size diameter of
the polymeric microparticles is from about 0.05 to about 5,000 microns. In an embodiment, the
unexpanded volume average particle size diameter of the polymeric microparticles is from about
0.1 to about 3 microns. In another embodiment, the unexpanded volume average particle size
diameter of the polymeric microparticles is from 0.1 to about 1 microns. In yet another
embodiment, the unexpanded volume average particle size diameter of the polymeric
microparticles is from about 0.05 to about 50 microns.
[0050] Representative preparations of cross linked polymeric microparticles using
microemulsion process are described in U.S. Pat. Nos. 4,956,400; 4,968,435; 5,171,808;
5,465,792 and 5,737,349.
[0051] In an inverse emulsion or microemulsion process, an aqueous solution of
monomers and crosslinkers is added to a hydrocarbon liquid containing an appropriate surfactant
or surfactant mixture to form an inverse monomer microemulsion consisting of small aqueous
droplets dispersed in the continuous hydrocarbon liquid phase and subjecting the monomer
microemulsion to free radical polymerization.
[0052] In addition to the monomers and crosslinkers, the aqueous solution may also
contain other conventional additives including chelating agents to remove polymerization
inhibitors, pH adjusters, initiators and other conventional additives.
[0053] The hydrocarbon liquid phase comprises a hydrocarbon liquid or mixture of
hydrocarbon liquids. Saturated hydrocarbons or mixtures thereof are preferred. Typically, the
hydrocarbon liquid phase comprises benzene, toluene, fuel oil, kerosene, odorless mineral spirits
and mixtures of any of the foregoing.
[0054] Surfactants useful in the microemulsion polymerization process described herein
include sorbitan esters of fatty acids, ethoxylated sorbitan esters of fatty acids, and the like or
mixtures thereof. Preferred emulsifying agents include ethoxylated sorbitol oleate and sorbitan
sesquioleate. Additional details on these agents may be found in McCutcheon's Detergents and
Emulsifiers, North American Edition, 1980.
[0055] Polymerization of the emulsion may be carried out in any manner known to those
skilled in the art. Initiation may be effected with a variety of thermal and redox free-radical
initiators including azo compounds, such as azobisisobutyronitrile; peroxides, such as t-butyl
10
peroxide; organic compounds, such as potassium persulfate and redox couples, such as sodium
bisulfite/sodium bromate. Preparation of an aqueous product from the emulsion may be effected
by inversion by adding it to water which may contain an inverting surfactant.
[0056] Polymeric microparticles cross linked with hydrolytically labile silyl ether or silyl
ester crosslinkers may be further cross linked by internally cross linking polymer particles which
contain polymers with pendant carboxylic acid and hydroxyl groups. The cross linking is
achieved through the ester formation between the carboxylic acid and hydroxyl groups. The
esterification can be accomplished by azeotropic distillation (U.S. Pat. No. 4,599,379) or thin
film evaporation technique (U.S. Pat. No. 5,589,525) for water removal. For example, a polymer
microparticle prepared from inverse emulsion polymerization process using acrylic acid, 2-
hydroxyethylacrylate, acrylamide and 2-acrylamido-2-methylpropanesulfonate sodium as
monomer is converted into cross linked polymer particles by the dehydration processes described
above.
[0057] The polymeric microparticles are optionally prepared in dry form by adding the
emulsion to a solvent which precipitates the polymer such as isopropanol, isopropanol/acetone or
methanol/acetone or other solvents or solvent mixtures that are miscible with both hydrocarbon
and water and filtering off and drying the resulting solid.
[0058] An aqueous suspension of the polymeric microparticles may be prepared by
redispersing the dry polymer in water.
[0059] The hydrolytically labile silyl ether or silyl ester crosslinkers may be prepared by
condensation of vinyl or allyl alcohols with alkoxysilanes, amiosilanes or halosilanes.
Representative alkoxysilanes, amiosilanes or halosilanes include tetrapropoxysilane,
tetramethoxysilane, 5-hexenyldimethylchlorosilane, 5-hexenyltrichlorosilane,
allyldimethylchlorosilane, 10-undecenyltrichlorosilane, vinylmethyldichlorosilane,
vinylmethyldiethoxysilane, vinyltrimethoxysilane, bis{p-aminophenoxy)dimethylsilane, 3-
aminopropyltrimethoxysilane, and the like. For example, a hydrolytically labile multifunctional
siloxane crosslinker can be readily prepared from tetrapropoxysilane by alcoholysis with excess
allyl alcohol followed by distillation of propanol. Changing the molar ratio of the
tetrapropoxysilane or vinyltrimethoxysilane to allyl alcohol can result in tri-functional or bifunctional
crosslinkers.
[0060] Another type of hydrolytically labile siloxane includes poly(sily ester)s where the
degradative properties can vary depending on the substituents attached to the silicone atoms and
carbonyl groups of the silyl ester linkages. A representative silyl ester material that can be
readily converted into a silyl ester crosslinker is (3-acryloxypropyl)dimethyl methoxysilane.
11
Poly(silyl ester) crosshnkers may be prepared by transsilylation ester interchange reactions. The
preparation of poly(silyl ester)s has been described in the literature. See, for example, M. Wang
et al., Macromolecules, 2000,33, 734.
[0061] In an embodiment, the hydrolytically labile silyl ether and silyl ester crosslinkers
have formula RiR2R3Si[OSiR4Rs]nR6 wherein Ri, R2, R3, R4, R5 and Rg are independently
selected from vinyl, vinyloxy, allyoxy or allyl, alkyl, aryl, alkoxy, arylalkyl and -OC(0)RA
where n is 0-100, provided that said crosslinkers comprise at least two vinyl, vinyloxy, allyoxy or
allyl groups, or a mixture thereof.
[0062] In an embodiment, Ri, R2, R» and R5 are alkyl and R3 and R6 are independently
selected from -CH2-CH=CH2 and-0-CH2-€H=CH2.
[0063] Upon injection into a subterranean formation, the polymeric microparticles flow
through the zone or zones of relatively high permeability in the subterranean formation under
increasing temperature conditions, until the composition reaches a location where the
temperature or pH is sufficiently high to promote expansion of the microparticles.
[0064] Unlike conventional blocking agents such as polymer solutions and polymer gels
that cannot penetrate far and deep into the formation, the composition of this invention, due to
the size of the particles and low viscosity, can propagate far from the injection point until it
encounters the high temperature zone.
[0065] Among other factors, the reduction in crosslinking density is dependent on the rate
of cleavage of the hydrolytically labile silyl ether ether or silyl ester crosslinkers and any
additional labile crosslinkers. In particular, hydrolytically labile silyl ether ether or silyl ester
crosslinkers and different labile crosslinkers, have different rates of bond cleavage at different
temperatures. The temperature and mechanism depend on the nature of the cross-linking
chemical bonds. For example, It is known that silyl ether and silyl ester bonds are susceptible to
hydrolysis under acidic and basic conditions. The degradation profile of these linkages can be
tuned by varying the substiutents attached to the silicone and carbon atoms of the crosslinkers.
Highly bulky substituents or substituents with different electronic character can alter the
degradative properties of these labile linkages.
[0066] In addition to the rate of de-crosslinking, and without wishing to be bound to any
theory, it is believed that the rate of particle diameter expansion also depends on the total amount
of remaining crosslinking. We have observed that the particle expands gradually initially as the
amount of crosslinking decreases. After the total amount of crosslinking passes below a certain
critical density, the viscosity increases explosively. Thus, by proper selection of the
hydrolytically labile silyl ether ether or silyl ester crosslinkers and additional labile crosslinkers,
12
both temperature- and time-dependent expansion properties can be incorporated into the polymer
particles.
[0067] The particle size of the polymer particles before expansion is selected based on
the calculated pore size of the highest permeability thief zone. The crosslinker type and
concentration, and hence the time delay before the injected particles begin to expand, is based on
the temperature both near the injection well and deeper into the formation, the expected rate of
movement of injected particles through the thief zone and the ease with which water can
crossflow out of the thief zone into the adjacent, lower permeability, hydrocarbon containing
zones. A polymer microparticle composition designed to incorporate the above considerations
results in a better water block after particle expansion, and in a more optimum position in the
formation.
[0068] An aspect of the present disclosure, therefore, is a method for diverting fluids
injected into a subterranean formation to achieve improved hydrocarbon fluid recovery from the
formation. In an embodiment, highly cross linked expandable polymeric microparticles having
unexpanded volume average particle size diameters of about 0.05 to about 5,000 microns made
with cross linking agent contents of about 100 to about 200,000 ppm of hydrolytically labile silyl
ether or silyl ester crosslmkers and from 0 to about 300 ppm of non-labile crosslinkers may be
injected into a subterranean formation to enhance oil recovery, to modify the permeability of the
subterranean formation and to increase the mobilization and/or recovery rate of hydrocarbon
fluids present in the formations.
[0069] There are many benefits that result from the use of the polymeric microparticles
having hydrolyzable silyl ester or silyl ether crosslinkers. These crosslinkers provide copolymers
having small particle size distributions and densities a conformation that is constrained such that
the copolymer is able to efficiently traverse and propagate through the pore structure of a
hydrocarbon fluid reservoir. As the polymeric microparticles traverse the reservoir formation
and are exposed to water, increased temperatures and varying pH levels in the formation, the
hydrolytically-labile cross links break, thereby allowing the polymeric microparticle to expand.
Upon breakage of at least a portion of the cross links, the polymeric microparticles expand to
form an expanded siloxane network wherein the size of the microparticles is greatly increased by
absorption of the carrier fluid that is injected into the well. Typically, the carrier fluid is water.
However, the skilled artisan will appreciate that the carrier fluid may be any carrier fluid known
in the art and used for the recovery of hydrocarbon fluids from subterranean formations.
[0070] Moreover, the use of polymeric microparticles having hydrolytically labile silyl
ether or silyl ester crosslinkers offers several benefits with respect to the activity or behavior of
13
the microparticles. For example, in embodiments where the hydrolytically labile silyl ether or
silyl ester crosslinkers comprise divinyl silyl ether crosslinkers having various alkyl lengths and
structures, the crosslinkers allow for greater control of the rate of hydrolysis of the crosslinkers
and, therefore, greater control of the expansion of the polymeric microparticles within the
subterranean formation. Similarly, polymeric microparticles having divinyl silyl ester
crosslinkers may also change the adhesive properties of the microparticles with respect to the
subterranean formation. As such, the polymeric microparticles may undergo a chemical reaction
when placed in contact with the subterranean formation such that charge of the microparticles
allows the microparticles to adhere to the subterranean formation via molecular forces.
[0071] In an embodiment, the composition includes cross linked anionic, cationic,
amphoteric, ion-pair or betaine-containing polymeric microparticles.
[0072] In an embodiment, the composition is in the form of an emulsion or aqueous
suspension.
[0073] In an embodiment, at least one of the cross linked polymeric microparticles is
anionic. The anionic polymeric microparticle may be prepared by free-radical polymerization
from about 95 to about 10 mole percent of nonionic monomers and from about 5 to about 90
mole percent anionic monomers. The nonionic monomer may be acrylamide and the anionic
monomer may be 2-acrylamido-2-methyl-l-propanesulfonic acid.
[0074] In an embodiment, at least one of the cross linked polymeric microparticles is
cationic. The cationic polymeric microparticles may be prepared by free-radical polymerization
of nonionic monomers with cationic monomers. In an embodiment, the cationic monomer may
be diallyldimethyl ammonium chloride (DADMAC).
[0075] In an embodiment, the non-labile cross linker is methylene bisacrylamide.
[0076] The diameter of the expanded polymeric microparticles may be greater than one
tenth of the controlling pore throat radius of the rock pores in the subterranean formation.
Alternatively, the diameter of the expanded polymeric microparticles may be greater than one
fourth of the controlling pore throat radius of the rock pores in the subterranean formation.
[0077] The ability of silyl ester or silyl ether crosslinkers to hydrolyze in the presence of
water is also important because the hydrolyzed silyl ester or silyl ether will produce structured
gels that aid in improving recovery of hydrocarbon fluids from subterranean formations. The
expanded monomers that form the structure gel are designed to have a particle size distribution
and physical characteristics such as, for example, the rheology of the expanded monomer
dispersion or solution, that allow the expanded monomers to impede the flow of fluids that are
injected into the subterranean formation. For example, the expanded monomers allow for
14
improved wettability of the surface of the subterranean formation and, thus, allow for improved
propagation into the pores of the formation. Upon deeper penetration into the formation, the
expanded monomers are capable of blocking preferred fluid pathways in order to divert a chase
fluid into less thoroughly swept zones of the reservoir. As such, the polymer application of the
polymeric microparticles is able to provide improved recovery of hydrocarbon fluids from
subterranean formations.
[0078] Accordingly, in another aspect of the present disclosure, methods of using the
above-described compositions are provided. The methods are directed toward improving
recovery of hydrocarbon fluids from a subterranean formation comprising injecting into the
subterranean formation one or more of the compositions previously described herein, as well as
variations and/or combinations thereof.
[0079] In an embodiment, the composition is added to injection water as part of a
secondary or tertiary process for the recovery of hydrocarbon fluids from the subterranean
formation. The injection water may be added to the subterranean formation at a temperature
lower than the temperature of the subterranean formation. The injection water may also be added
directly to a producing well.
[0080] The composition may be added to the injection water in any amount, based on
polymer actives, effective to improve recovery of hydrocarbon fluids from the formation. For
example, in an embodiment, from about 100 ppm to about 10,000 ppm of the composition, based
on polymer actives, is added to the subterranean formation. In another embodiment, from about
500 ppm to about 1,500 ppm of the composition, based on polymer actives, is added to the
subterranean formation. In yet another embodiment, from about 500 ppm to about 1,000 ppm of
the composition, based on polymer actives, is added to the subterranean formation.
[0081] In an embodiment, the composition is used in a carbon dioxide and water tertiary
recovery project.
[0082] In an embodiment, the composition is used in a tertiary oil recovery process, one
component of which constitutes water injection.
[0083] In an embodiment, the subterranean formation is a sandstone or carbonate
hydrocarbon reservoir.
[0084] The foregoing 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 the
present disclosure.
EXAMPLE 1
15
[0085] Sand Pack Test
[0086] This Example demonstrates that the polymeric microparticles of this invention can
be propagated with a conformation constrained by the built-in reversible crosslinks and will
expand in size when these break, to give a particle of suitable size to produce a substantial effect.
[0087] In the sand pack test, a 40 foot long sand pack of 0.25 inches internal diameter,
made from degreased and cleaned 316 stainless steel tubing, is constructed in eight sections,
fitted with pressure transducers, flushed with carbon dioxide gas and then placed in an oven and
flooded with synthetic oil field injection water.
[0088] A dispersion of a representative polymeric microparticles is prepared in the
synthetic injection water and injected into the pack to fill the pore volume. Pressure drops across
the tube sections are monitored for signs of conformation change of the polymer particle as the
reversible cross-links are hydrolysed. The "popping open" of the polymer particles is observed
as a steep rise in the pressure drop. The sand pack test is described in detail in WO 01/96707.
[0089] The data for representative polymeric microparticles shows that the particles are
able to travel through the first two sections of the sand pack without changing the RRF of the
sections. However, particles in the last section, after accumulating a sufficient amount of
residence time, have expanded and give a higher value of RRF. The higher RRF value is
maintained after the injection fluid is changed from polymer dispersion to brine.
[0090] This experiment clearly demonstrates two aspects of the invention which are:
[0091] 1. The polymeric microparticles with a conformation constrained by the
built-in reversible crosslinks can be propagated through a porous media
[0092] 2. The microparticles will expand in size when crosslinks break, to give a
particle of suitable size to produce a substantial effect, even in a high permeability porous
medium.
EXAMPLE 2
[0093] Activation of the Polymeric Microparticles by Heat
[0094] As the particles expand in a medium of fixed volume, the volume fraction
occupied by them increases. Consequently, the volume fraction of the continuous phase
decreases. This decrease in free volume is reflected in an increase in the viscosity of the
dispersion. Activation of the microparticles of present disclosure by heat can be demonstrated in
a bottle test.
[0095] To carry out a bottle test, a dispersion containing 5000 ppm of the kernel particles
is prepared in an aqueous medium (e.g., a synthetic brine). Dispersing of particles can be
16
accomplished by vigorous stirring or by using a homogenizer. To prevent oxidative degradation
of the expanding particles during monitoring, 1000 ppm sodium thiosulfate can be added to the
mixture as an oxygen scavenger.
[0096] The bottles were placed in a constant temperature oven to age. Then, at a
predetermined time, a bottle can be removed from the oven and cooled to 75oF. The viscosity
was measured at 75 °F using Brookfield LV No. 1 spindle at 60 rpm (shear rate 13.2 sec"1).
[0097] Activation of the polymeric microparticles by heat can be demonstrated by
monitoring the viscosity change of aqueous dispersions of particles aged at different temperature.
[0098] It should be understood that various changes and modifications to the presently
preferred embodiments described herein will be apparent to those skilled in the art. Such
changes and modifications can be made without departing from the spirit and scope of the
present subject matter and without diminishing its intended advantages. It is therefore intended
that such changes and modifications be covered by the appended claims.

CLAIMS
The invention is claimed as follows:
1. A composition comprising highly cross linked expandable polymeric microparticles
having unexpanded volume average particle size diameters of about 0.05 to about 5,000 microns
and a cross linking agent content of from 0 to about 300 ppm of non-labile cross linking agents
and from about 100 to about 200,000 ppm of labile crosslinking agents, wherein said labile
crosslinking agents comprise one or more hydrolytically labile silyl ether or silyl ester
crosslinkers.
2. The composition of claim 1 wherein said hydrolytically labile crosslinkers have formula
RiR.2R3Si[OSiR4R5]„R6 wherein Ri, R2, R3, R4, R5 and R6 are independently selected from vinyl,
vinyloxy, allyoxy, acryloxy, methacryloxy, allyl, alkyl, aryl, alkoxy, arylalkyl and -OC(0)Rg
where n is 0-100, provided that said crosslinkers comprise at least two vinyl, vinyloxy, allyoxy,
acryloxy, methacryloxy or allyl groups, or a mixture thereof.
3. The composition of Claim 1, wherein the unexpanded volume average particle size
diameter is from about 0.1 to about 3 microns.
4. The composition of Claim 1, wherein the unexpanded volume average particle size
diameter is from about 0.1 to about 1 micron.
5. The composition of Claim 1, comprising cross linked anionic, cationic, amphoteric, ionpair
or betaine-containing polymeric microparticles.
6. The composition of claim 2 wherein Ri, R2, R4 and R5 are alkyl and R3 and R6 are
independently selected from -CH2-CH=CH2 and-(W:H2-CH=CH2.
7. The composition of Claim 1, wherein the composition is in the form of an emulsion or
aqueous suspension.
8. The composition of Claim 7, wherein the cross linked polymeric microparticle is anionic.
18
9. The composition of Claim 8, wherein the anionic polymeric microparticle is prepared by
free-radical polymerization from about 95 to about 10 mole percent of nonionic monomers and
from about 5 to about 90 mole percent anionic monomers.
10. The composition of Claim 9, wherein the nonionic monomer is acrylamide.
11. The composition of Claim 10, wherein the anionic monomer is 2-acrylamido-2-methyl-lpropanesulfonic
acid.
12. The composition of Claim 1, wherein the non-labile cross linker is methylene
bisacrylamide.
13. The composition of claim 1 further comprising one or more labile crosslinkers.
14. The composition of claim 1 further comprising one or more highly cross linked
expandable polymeric microparticles having unexpanded volume average particle size diameters
of about 0.05 to about 5,000 microns and a cross linking agent content of from 0 to about 300
ppm of non-labile cross linking agent and from about 100 to about 200,000 ppm of labile
crosslinking agent.
15. A method for improving recovery of hydrocarbon fluids from a subterranean formation
comprising injecting into the subterranean formation a composition comprising highly cross
linked expandable polymeric microparticles comprising hydrolytically labile silyl ether and silyl
ester crosslinkers according to claim 1, wherein the microparticles have a smaller diameter than
the pores of the subterranean formation and wherein the hydrolytically labile crosslinkers break
under the conditions of temperature and pH in the subterranean formation to form expanded
microparticles.
16. The method of Claim 15, wherein from about 100 ppm to about 10,000 ppm of the
composition, based on polymer actives, is injected into the subterranean formation.
17. The method of Claim 15, wherein the composition is added to injection water as part of a
secondary or tertiary process for the recovery of hydrocarbon fluids from the subterranean
formation.
19
18. The method of Claim 15, wherein the composition is used in a carbon dioxide and water
tertiary recovery project.
19. The method of Claim 15, wherein the composition is used in a tertiary oil recovery
process, one component of which constitutes water injection.
20. The method of Claim 15, wherein the subterranean formation is a sandstone or carbonate
hydrocarbon reservoir.
20
21. A composition substantially as herein described with reference to the foregoing description
and the accompanying examples.
Dated this 12th day of November 2010
To
The Controller of Patents
The Patent Office
India
HARAD VADEHRA
FKANAN/KRISHME
RNEY FOR/THE APPLICANTS