Title of Invention	"BLOCK COPOLYMERS FOR RECOVERING HYDROCARBON FLUIDS FROM A SUBTERRANEAN RESERVOIR"
Abstract	The present disclosure is directed to compositions and methods that may be used for enhanced oil recovery, for modifying the permeability of subterranean formations and for increasing the mobilization and/or recovery rate of hydrocarbon fluids present in the formations. The compositions may include, for example, expandable cross-linked polymeric microparticles having unexpanded volume average particle size diameters of from about 0.05 to about 5,000 microns and cross linking agent contents of from about 100 to about 200,000 ppm of labile cross linkers and from 0 to about 300 ppm of non-labile cross linkers, wherein the expandable polymeric monomers have a block copolymer structure comprising at least two different monomers having different chemical structures.

Title of Invention

"BLOCK COPOLYMERS FOR RECOVERING HYDROCARBON FLUIDS FROM A SUBTERRANEAN RESERVOIR"

Abstract

The present disclosure is directed to compositions and methods that may be used for enhanced oil recovery, for modifying the permeability of subterranean formations and for increasing the mobilization and/or recovery rate of hydrocarbon fluids present in the formations. The compositions may include, for example, expandable cross-linked polymeric microparticles having unexpanded volume average particle size diameters of from about 0.05 to about 5,000 microns and cross linking agent contents of from about 100 to about 200,000 ppm of labile cross linkers and from 0 to about 300 ppm of non-labile cross linkers, wherein the expandable polymeric monomers have a block copolymer structure comprising at least two different monomers having different chemical structures.

Full Text	TITLE "BLOCK COPOLYMERS FOR RECOVERING HYDROCARBON FLUIDS FROM A SXJBTERRANEAN RESERVOIR" 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 temas of fiiel 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 1 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. [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 the prematurely swept zone, or the 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 v^iien 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 2 and 5,735,349. 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. [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 reversible (l^^bile) internal crosslinks. 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 labile cross linker. 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, the present disclosure is directed to compositions comprising highly cross linked expandable polymeric microparticles having unexpanded volume average particle size diameters of from about 0.05 to about 5,000 microns and cross linking agent contents of from about 100 to about 200,000 ppm of labile cross linkers and from 0 to about 300 3 ppm of non-labile cross linkers, wherein the expandable polymeric microparticles have a block copolymer structure that includes at least two different monomers having different chemical structures. [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] "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. Preferred amphoteric polymeric microparticles have a higher than 1:1 anionic monomericationic monomer mole ratio. [0021] "Ampholytic ion pair monomer" means the acid-base salt of basic, nitrogen containing monomers such as dimethylaminoethylacrylate (DMAEA), dimethylaminoethyl methacrylate (DMAEM), 2-methacryloyloxyethyldiethyIamine, and the like and acidic monomers such as acrylic acid and sulfonic acids such as 2-acrylamido-2-methylpropane sulfonic acid, 2-methacryloyIoxyethane sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid, and the like. [0022] "Anionic monomer" means a monomer as defined herein which possesses an acidic fiinctional 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 water-soluble forms of these or other polymerizable carboxylic or sulphonic acids, sulphomethylated acrylamide, aliyl sulphonic acid, vinyl sulphonic acid, the quaternary salts of acrylic acid and methacrylic acid such as ammonium acrylate and ammonium methacrylate, and the like. Preferred anionic monomers include 2-acrylamido-2-methyl propanesulfonic acid sodium salt, vinyl sulfonic acid sodium salt and styrene sulfonic acid sodiimi salt. 2-Acrylamido- 2-methyl propanesulfonic acid sodiimi salt is more preferred. [0023] "Anionic polymeric microparticle" means a cross-linked polymeric microparticle containing a net negative charge. Representative anionic polymeric microparticles include 4 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-acrylaniido-2-methyl propane sulfonic acid. Preferred 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. More preferred 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. [0024] "Betaine-containing polymeric microparticle" means a cross-linked polymeric microparticle prepared by polymerizing a betaine monomer and one or more nonionic monomers. [0025] "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-dimethyl-N-acryloyioxyethyl-N-(3-sulfopropyl)- ammonium betaine, N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine, N,N-dimethyI-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine, N,Ndunethyl- N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine, N,N-dunethyl-Nacryloxyethyl- N-(3 -sulfopropyl)-ammomum betaine, N,N-dLmethyl-N-acrylamidopropyl-N-(2- carboxymethyl)-amraomum betaine, N-3-sulfopropylvinylpyridine ammonium betaine, 2- (methylthio)ethyl methacryloyl-S-(sulfopropyl)-sulfomum betaine, l-(3-sulfopropyl)-2- vinylpyridinium betaine, N-(4-sulfobutyl)-N-methyldiaIlylamine ammonium betaine (MDABS), N,N-diaIlyI-N-methyl-N-(2-sulfoethyl) airmionium betaine, and the like. A preferred betaine monomer is N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine. [0026] "Block copolymers" means any type of long sequences of the same monomer unit bound by covalent bonds. The blocks can be connected in a variety of ways. Examples of block copolymers include, but are not limited to, segmented blocks, random blocks, di-blocks, triblocks, alternating blocks, periodic blocks, amphiphilic blocks, statistical blocks, star blocks and comb blocks. Synthetic details on each type of block varies. However, the varied synthetic details may provide distinctive performance advantages in application. Recently, block copolymer synthesis has received a greater amount of attention because of controlled radical polymerizations, mcluding, for example, atom transfer radical polymerization (ATRP), nitroxidemediated radical polymerization (NMP), and revisible addition fragmentation chain transfer polymerization (RAFT); See, Braunecker, W. A. et al. Prog. Polym. Sci. 2007, 32, 93. These new methods provide better control over the block synthesis, as well as synthesis of novel block copolymers. There are many examples of block copolymer synthesis using 5 controlled radical polymerization in the literature. The most common method for the preparation of vinyl monomers is the sequential addition of the monomers. This can be extended if the sequential polymerization is terminated with a functional group such as alkoxyamine, which can be used as a macroinitiator to prepare a new block. Tenhu et al, reports the synthesis of A-B-A block copolymers of poly(N-isopropylacrylamide) as a hydrophilic block and a non-water-soluble-block consisting of poly((3-methoxypropyl)acrylamide) (PMPAM) are synthesized using RAFT polymerizations. In this reaction, a bifunctional S,S'-bis(a, a'-dimethyla"- acetic acid)-trithiocarbonate is used as a RAFT agent to obtain the A-B-A block copolymer. See, Nuopponen et al, J. of Polymer Science, A Poly Chem. 2008, 46, 38. Further, BlocBuilder®, introduced by Arkema, is a double headed alkoxyamine initiator which will lead to triblocks. If a single headed initiator is used, the polymer produced will be a simple diblock copolymer. Blockcopolymers of various composition and morphology will result in polymers with different properties, which can lead to polymers that behave and perform differently. [0027] "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, dimetliylaminoethylacrylate sulfuric acid salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt (DMAEABCQ) and dimethylaminoethylacrylate methyl sulfate quaternary salt; the quaternary or acid salts of dialkylaminoalkylacrylamides and methaciylamides 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 ammoniiun chloride (DADMAC). Preferred cationic monomers include dimethylaminoethylacrylate methyl chloride quaternary salt, dimethylaminoethyhnethacrylate methyl chloride quaternary salt and diallyldimethyl ammonium chloride. Diallyldimethyl ammonium chloride is more preferred. [0028] "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 6 microparticle configuration. Cross linking monomers according to this invention include both labile cross linking monomers and non-labile cross linking monomers. [0029] "Emulsion." "microemulsion" and "inverse emulsion" mean a water-in-oil polymer emulsion comprising a polymeric microparticle according to this invention in the aqueoijs 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 poljmiers dispersed within the hydrocarbon matrix. The emulsion polymer are optionally "inverted" or converted into water-continuous form using shear, dilution, and, generally an inverting surfactant. See, U.S. Pat. No. 3,734,873, the entire content of \^iuch is incorporated herein by reference. [0030] "Fluid mobility" means a ratio that defmes how readily a flxiid moves through a porous meditim. 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. [0031] When more than one fluid is flowing the end point relative permeabilities must be substituted for the absolute permeability used in equation 1. 2. /Lt = — for a fluid x flowing in a porous medium in the presence of one or more other fluids. [0032] When two or more fluids are flowmg the fluid mobilities may be used to define a Mobility ratio 3. M = —= - ^ Xy TJxkry [0033] 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, 7 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. [0034] "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. [0035] "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 trimethactylate, ethoxylated trimethylol triacrylate, ethoxylated pentaerj^thritol 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. Preferred labile cross linking monomers include water soluble diacrylates such as PEG 200 diacrylate and PEG 400 diacrylate and poljrfimctional vinyl derivatives of a polyalcohol such as ethoxylated (9-20) trimethylol triacrylate. [0036] In an embodiment, the labile cross linkers are present in an amount of about 100 to about 200,000 ppm, based on total weight of monomer. In another embodiment, the labile cross linkers are present in an amount from about 1,000 to about 200,000 ppm. In another embodiment, the labile cross linkers are present in an amount from about 9,000 to about 200,000 ppm. In another embodiment, the labile cross linkers are present in an amount from about 9,000 to about 100,000 ppm. In another embodiment, the labile cross linkers are present in an amount from about 20,000 to about 60,000 ppm. In another embodiment, the labile cross linkers are present in an amount from about 500 to about 50,000 ppm. In another embodiment, the labile crosslinkers are present in an amount of about 1,000 to about 20,000 ppm. [0037] "Monomer" means a polymerizable allylic, vinylic or acrylic compound. The monomer may be anionic, cationic, nonionic or zwitterionic. Vinyl monomers are preferred, acrylic monomers are more preferred. [0038] "Nonionic monomer" means a monomer as defined herein which is electrically neutral. Representative nonionic monomers include N-isopropylacrylamide, N,Ndimethylacrylamide, N,N-diethyIacrylamide, dimethylaminopropyl acrylamide, 8 dimethylaminopropyl methacrylamide, acryloyl morpholine, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, dimethylaminoethylacrylate (DMAEA), dimethylaminoethyl methacrylate (DMAEM), maleic anhydride, N-vmyl pyrrolidone, vinyl acetate and N-vinyl formamide. Preferred nonionic monomers include acrylamide, N-methylacrylamide, N,N-dimethylacrylamide and methacrylamide. Acrylamide is more preferred. [0039] "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 monomer 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. A preferred non-labile cross linking monomer is methylene bisacrylamide. [0040] 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 'structure.' Such 'structured' particles can block the pore throats of porous media and create a blockage of flow. [0041] 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 9 diameter of the polymeric microparticles is from 0.1 to about 1 microns. In another embodiment, the unexpanded volume average particle size diameter of the polymeric microparticles is from about 0.05 to about 50 microns. [0042] 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. [0043] In an inverse emulsion or microemulsion process, an aqueous solution of monomers and cross liiikers is added to a hydrocarbon liquid containing an ^propriate surfactant or surfactant mixture to form an inverse monomer microemulsion consisthig of small aqueous droplets dispersed in the continuous hydrocarbon liquid phase and subjecting the monomer microemulsion to free radical polymerization. [0044] In addition to the monomers and cross linkers, the aqueous solution may also contain other conventional additives including chelating agents to remove polymerization mhibitors, pH adjusters, initiators and other conventional additives. [0045] 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, ftiel oil, kerosene, odorless mineral spirits and mixtures of any of the foregoing. [0046] Surfactants useftil 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. [0047] 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-bxityl 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 [0048] Alternatively, the polymeric microparticles cross linked with labile cross links are prepared 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. 10 5,589,525) for water removal. For example, a polymer microparticle prepared from inverse emulsion polymerization process usir^ 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. [0049] 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. [0050] An aqueous suspension of the polymeric microparticles is prepared by redispersing the dry polymer in water. [0051] Upon injection into a subterranean formation, the polymeric microparticles flow through the a 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, [0052] 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 &om the injection point until it encounters the high temperature zone. [0053] Also, the polymeric microparticles of this invention, due to their highly crosslinked nature, do not expand in solutions of different salinity. Consequently, the viscosity of the dispersion is not affected by the salinity of the fluid encountered in the subterranean formation. Accordingly, no special carrier fluid is needed for treatment. Only after the particles encounter conditions sufficient to reduce the crosslinking density, is the fluid rheology changed to achieve the desired effect [0054] Among other factors, the reduction in crosslinking density is dependent on the rate of cleavage of the labile crosslinker. In particular, 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, when the labile crosslinker is PEG diacrylate, hydrolysis of the ester linkage is the mechanism of de-crosslihking. Different alcohols have slightly different rates of hydrolysis. In general, methacrylate esters will hydrolyze at a slower rate than acrylate esters under similar conditions. With divinyl or diallyl compounds separated by an azo group such as the diallylamide of 2,2'-Azobis(isbutyric acid), the mechanism of de-crosslinking is elimination of a nitrogen molecule. As demonstrated by various azo 11 initiators for free radical polymerization, different azo compounds indeed have different half-life temperatures for decomposition. [0055] 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 labile crosslinker, both temperature- and time-dependent expansion properties can be incorporated into the polymer particles. [0056] 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. [0057] An aspect of the present disclosure is to demonstrate the benefits that result fiom the use of expandable polymeric microparticles having a block copolymer structures. Block copolymers of various composition and morphology will result in polymers with different properties and behavior that will aid in improving recovery of hydrocarbon fluids from subterranean formations. For example, application of a composition of expandable polymeric microparticles having a block copolymer structure may improve properties including, but not limited to, the binding, diffusion and rate of expansion of the polymeric microparticles. [0058] In an embodiment, a composition is provided that includes highly cross linked expandable poljoneric microparticles having unexpanded volume average particle size diameters of about 0.05 to about 5,000 microns and cross linking agent contents of about 100 to about 200,000 ppm of labile cross linkers and from 0 to about 300 ppm of non-labile cross linkers, wherein the expandable polymeric microparticles have a block copolymer structure having at least two different monomers having different chemical structures. The block copolymer structure may be any block copolymer structure known in the art. For example, the block copolymer structure may include segmented blocks, random blocks, di-blocks, tri-blocks, alternating blocks, periodic blocks, amphiphilic blocks, statistical blocks, star blocks, comb 12 blocks and combinations thereof. In an embodiment, the block copolymer includes a hydrophilic block of poly(N-isopropylacrylamide) and a non-water-soluble block of poly((3- methoxypropyl)acrylamide). [0059] The expandable polymeric microparticles having the block copolymer structure may be synthesized by any method known in the art. For example, the expandable polymeric microparticles having the block copolymer structure may be synthesized by methods including, but not limited to, controlled radical polymerization, anionic polymerization, cationic polymerization, group transfer polymerization, olefin metathesis polymerization, postpolymerization formation of metal complexes, and transition metal-catalyzed polymerization. In an embodiment, the expandable polymeric microparticles having the block copolymer structure is synthesized by controlled radical polymerization. [0060] In an embodiment where the expandable polymeric microparticles having the block copolymer structure are synthesized by controlled radical polymerization, the controlled radical polymerization technique may be any controlled radical polymerization technique known in the art For example, the controlled radical polymerization technique may include, but is not limited to, atom transfer radical polymerization (ATRP), nitroxide-mediated radical polymerization (NMP), and reversible addition fragmentation chain transfer polymerization (RAFT). [0061] Because an embodiment of the present disclosure comprises a composition of at least two different monomers having different chemical structures, the at least two different monomers may have any number of characteristics that differ from each other. For example, the monomers may have different molecular weights, hydrophobicity or hydrophilicity. Differences in the chemical structures and, therefore, the inherent properties of the different monomers allow for an improved behavior of the polymeric microparticles with respect to, for example, binding properties, diffusivity and the rate of expansion of the microparticles within the subterranean formation. [0062] The block copolymer structure of the polymeric microparticles in accordance with present disclosure may include any number of different monomer units. For example, in an embodiment, the block copolymer may include at least two different monomers, each of which have different chemical structures. Alternatively, in an embodiment, the block copolymer may also include a third monomer having a structure that is different from both of the at least two different monomers. The third monomer may be any monomer known in the art and may be selected based on the desired properties of the block copolymer. For example, a third monomer may be selected for its ability to modify the hydrophobicity or the hydrophilicity of the block 13 copolymer. Further, a third monomer may also be selected for its ability to either strengthen or assist in degrading the backbone of the polymer chain. Accordingly, the skilled artisan will appreciate that any number of different monomers may be used to synthesize the block copolymer structure of the polymeric microparticles. [0063] The unexpanded polymeric microparticles may have any average particle size diameter useful in appUcations to improve recovery of hydrocarbon fluids from subterranean formations. For ejcample, the unexpanded polymeric microparticles may have an average particle size diameter from about 0.05 to about 5,000 microns. In an embodiment, the unexpanded polymeric microparticles have an average particle size diameter from about 0,1 to about 5 microns. In an embodunent, the unexpanded polymeric microparticles have an average particle size diameter from about 0.1 to about 3 microns. In another embodiment, the unexpanded polymeric microparticles have an average particle size diameter from about 0.1 to about 1 micron. In another embodiment, the unexpanded polymeric microparticles have an average particle size diameter from about 0.05 to about 50 microns. [0064] In an embodiment, the labile cross Unker is selected from diacrylates and polyfimctional vinyl derivatives of a polyalcohol. The labile cross-linker may also be polymethyleneglycol diacrylate. [0065] In an embodiment, the composition includes cross linked anionic, amphoteric, ion-pair or betaine-containing polymeric microparticles. [0066] In an embodiment, the composition is in the form of an emulsion or aqueous suspension. [0067] 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. [0068] In an embodiment, the non-labile cross linker is methylene bisacrylamide. [0069] 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. [0070] 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 14 subterranean formation any of the compositions previously described herein, as well as variations or combinations thereof. [0071] For example, in an embodiment, a method for improving recovery of hydrocarbon fluids from a subterranean formation is provided. The method mcludes injecting into a subterranean formation highly cross linked expandable polymeric microparticles having unexpanded volume average particle size diameters of about 0.05 to about 5,000 microns and cross linking agent contents of about 100 to about 200,000 ppm of labile cross linkers and from 0 to about 300 ppm of non-labile cross linkers, wherein the expandable polymeric microparticles have a block copolymer structure comprising at least two different monomers having different chemical structures. The microparticles may have a smaller diameter than the pores of the subterranean formation and the labile cross linkers may break under the conditions of temperature and pH in the subterranean formation to form expanded microparticles. [0072] In an embodiment, the highly cross Imked expandable polymeric microparticles are 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. [0073] The composition of polymeric microparticles having a block copolymer structure may be added to the injection water in any amount, based on polymer actives, effective to improve recovery of hydrocarbon flxxids 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. [0074] In an embodiment, the injection into the subterranean formation of the highly cross linked expandable polymeric microparticles is used in a carbon dioxide and water tertiary recovery project. [0075] In an embodiment, the injection into the subterranean formation of the highly cross linked expandable polj^meric microparticles is used in a tertiary oil recovery process, one component of which constitutes water injection. [0076] In an embodiment, the subterranean formation is a sandstone or carbonate hydrocarbon reservoir. 15 [0077] 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 [0078] Preparation of the Polymeric Microparticle [0079] The polymeric microparticle of the present disclosure may be readily prepared using inverse emulsion polymerization techniques as described below. [0080] A representative emulsion polymer composition can be prepared in numerous ways by the sIdUed artisan. By way of example, a preparation method using (3- vinylphenyl)azomethylmalonodinitrile is provided herein. A representative emulsion polymer composition is prepared by polymerizing a monomer emulsion consisting of an aqueous mixture of 98.94 g of 50% acrylamide, 150 g of 58% sodium acrylamido methylpropane sulfonate (AMPS), 19.38 g water, 0.5 g 40% pentasodium diethylenetriaminepentaacetate, 0.2 g of (3- vinylphenyl)azomethylmalonodinitrile, and 36.24 g polyethyleneglycol (PEG) diacrylate as the dispersed phase and a mixture of 336 g petroleum distillate, 60 g ethoxylated sorbitol oleate and 4 g sorbitan sesquioleate as the continuous phase. [0081] The monomer emulsion is prepared by mixing the aqueous phase and the oil phase, followed by homogenization using a Silverson Homogenizer. After deoxygenation with nitrogen for 30 minutes, poljmierization is initiated by using redox initiators and kept under 35 "C. Once all of the monomer is polymerized, a second batch of monomers: 65.96 g of 50% acrylamide, 225 g of 58% sodium acrylamido methylpropane sulfonate (AMPS) is added to the reaction mixture. The reaction is slowly heated to 65 °C and held at that temperature until the monomer is converted to 50%. The temperature is then raised to 80 "C and held there until all of the monomer is converted. [0082] If desired, the polymeric microparticle can be isolated fixDm the latex by precipitating, filtering, and washing with a mixture of acetone and isopropanol. After drying, the oil and surfactant free particle can be redispersed in aqueous media. EXAMPLE 2 [0083] Sand Pack Test [0084] 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. 16 [0085] 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. [0086] 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. [0087] 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. [0088] This experiment clearly demonstrates two aspects of the invention which are: [0089] 1. The polymeric microparticles with a conformation constrained by the built-in reversible crosslinks can be propagated through a porous media. [0090] 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 3 [0091] Activation of the Polymeric Microparticles by Heat [0092] As the particles expand in a medium of fixed volume, the volume firaction 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. [0093] 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 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. 17 [0094] The bottles are placed in a constant temperature oven to age. Then, at a predetermined time, a bottle can be removed fix)m the oven and cooled to 75oF. The viscosity is measured at 75 T using Brookfield LV No.l spindle at 60 rpm (shear rate 13.2 sec"'). [0095] Activation of the polymeric microparticles by heat can be demonstrated by monitoring the viscosity change of aqueous dispersions of particles aged at different temperature. [0096] 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. 18 CLAIMS The invention is claimed as follows: 1. A composition comprising: highly cross linked expandable polymeric microparticles comprising unexpanded volume average particle size diameters of about 0.05 to about 5,000 microns and cross linking agent contents of about 100 to about 200,000 ppm of labile cross linkers and from 0 to about 300 ppm of non-labile cross linkers, wherein the expandable polymeric microparticles have a block copolymer structure comprising at least two different monomers having different chemical structures. 2. The composition of Claim 1, wherein the block copolymer structure is selected from the group consisting of segmented blocks, random blocks, di-blocks, tri-blocks, alternating blocks, periodic blocks, amphiphilic blocks, statistical blocks, star blocks, comb blocks, and combinations thereof. 3. The composition of Claim 1, wherein the block copolymer structure comprises a third monomer having a structure that is different from the structures of the at least two different monomers. 4. The composition of Claim 1, wherein the expandable polymeric microparticles having the block copolymer structure are synthesized using a controlled radical polymerization technique selected from the group consisting of atom transfer radical poljonerization, nitroxidemediated radical polymerization, reversible addition fragmentation chain transfer polymerization, and combinations thereof. 5. The composition of Claim 1, wherein the block copolymer structure comprises a hydrophilic block of poly(N-isopropylacrylamide) and a non-water-soluble block of poly((3- methoxypropyl)acrylamide). 6. The composition of Claim 1, wherein the unexpanded volume average particle size diameter is from about 0.1 to about 3 microns. 7. The composition of Claim 1, wherein the unexpanded volume average particle size diameter is from about 0.1 to about 1 micron. 19 8. The composition of Claim 1, wherein the labile cross linker is selected from diacrylates and polyfunctional vinyl derivatives of apolyalcohol. 9. The composition of Claim 1, comprising cross linked anionic, amphoteric, ionpair or betaine-containing polymeric microparticles. 10. The composition of Claim 10, wherein the composition is in the form of an emulsion or aqueous suspension. 11. The composition of Claim 11, wherein at least one of the cross linked polymeric microparticles is anionic. 12. The composition of Claim 12, wherein the anionic polymesric 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. 13. The composition of Claim 13, wherein the nonionic monomer is acrylamide and the anionic monomer is 2-acrylamido-2-methyl-l-propanesulfonic acid. 14. The composition of Claim 13, wherein the labile cross-linker is polymethyleneglycol diacrylate and the non-labile cross linker is methylene bisacrylamide. 15. A method for improving recovery of hydrocarbon fluids fix)m a subterranean formation comprising injecting into the subterranean formation a composition comprising highly cross linked expandable polymeric microparticles comprising according to claim 1, wherein the microparticles have a smaller diameter than the pores of the subterranean formation and wherein the labile cross linkers break under the conditions of temperature and pH in the subterranean formation to form expanded microparticles. 16. The method of Claim 15, vsiierein from about 100 ppm to about 10,000 ppm of the composition, based on polymer actives, is added to the subterranean formation. 20 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. 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. 21 21. A composition substantially as herein described with reference to the foregoing description and the accempanying examples. /Dated this 1st day of November 2010. / / / ' ^ v Sfiarad V^ehra ^ ^ ijfKAN Af^KRISHME REGISTEREj/PATENT AGENT To -^ The Controller of Patents The Patent Office Delhi

Full Text

TITLE
"BLOCK COPOLYMERS FOR RECOVERING HYDROCARBON FLUIDS FROM A
SXJBTERRANEAN RESERVOIR"
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 temas of fiiel 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
1
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.
[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 the prematurely swept zone, or the
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 v^iien 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
2
and 5,735,349. 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.
[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 reversible (l^^bile) internal crosslinks. 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 labile cross
linker. 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, the present disclosure is directed to compositions comprising
highly cross linked expandable polymeric microparticles having unexpanded volume average
particle size diameters of from about 0.05 to about 5,000 microns and cross linking agent
contents of from about 100 to about 200,000 ppm of labile cross linkers and from 0 to about 300
3
ppm of non-labile cross linkers, wherein the expandable polymeric microparticles have a block
copolymer structure that includes at least two different monomers having different chemical
structures.
[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] "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. Preferred amphoteric polymeric microparticles have a higher than
1:1 anionic monomericationic monomer mole ratio.
[0021] "Ampholytic ion pair monomer" means the acid-base salt of basic, nitrogen
containing monomers such as dimethylaminoethylacrylate (DMAEA), dimethylaminoethyl
methacrylate (DMAEM), 2-methacryloyloxyethyldiethyIamine, and the like and acidic
monomers such as acrylic acid and sulfonic acids such as 2-acrylamido-2-methylpropane
sulfonic acid, 2-methacryloyIoxyethane sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid,
and the like.
[0022] "Anionic monomer" means a monomer as defined herein which possesses an
acidic fiinctional 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
water-soluble forms of these or other polymerizable carboxylic or sulphonic acids,
sulphomethylated acrylamide, aliyl sulphonic acid, vinyl sulphonic acid, the quaternary salts of
acrylic acid and methacrylic acid such as ammonium acrylate and ammonium methacrylate, and
the like. Preferred anionic monomers include 2-acrylamido-2-methyl propanesulfonic acid
sodium salt, vinyl sulfonic acid sodium salt and styrene sulfonic acid sodiimi salt. 2-Acrylamido-
2-methyl propanesulfonic acid sodiimi salt is more preferred.
[0023] "Anionic polymeric microparticle" means a cross-linked polymeric microparticle
containing a net negative charge. Representative anionic polymeric microparticles include
4
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-acrylaniido-2-methyl propane sulfonic
acid. Preferred 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.
More preferred 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.
[0024] "Betaine-containing polymeric microparticle" means a cross-linked polymeric
microparticle prepared by polymerizing a betaine monomer and one or more nonionic monomers.
[0025] "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-dimethyl-N-acryloyioxyethyl-N-(3-sulfopropyl)-
ammonium betaine, N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl)-ammonium
betaine, N,N-dimethyI-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine, N,Ndunethyl-
N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine, N,N-dunethyl-Nacryloxyethyl-
N-(3 -sulfopropyl)-ammomum betaine, N,N-dLmethyl-N-acrylamidopropyl-N-(2-
carboxymethyl)-amraomum betaine, N-3-sulfopropylvinylpyridine ammonium betaine, 2-
(methylthio)ethyl methacryloyl-S-(sulfopropyl)-sulfomum betaine, l-(3-sulfopropyl)-2-
vinylpyridinium betaine, N-(4-sulfobutyl)-N-methyldiaIlylamine ammonium betaine (MDABS),
N,N-diaIlyI-N-methyl-N-(2-sulfoethyl) airmionium betaine, and the like. A preferred betaine
monomer is N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine.
[0026] "Block copolymers" means any type of long sequences of the same monomer unit
bound by covalent bonds. The blocks can be connected in a variety of ways. Examples of block
copolymers include, but are not limited to, segmented blocks, random blocks, di-blocks, triblocks,
alternating blocks, periodic blocks, amphiphilic blocks, statistical blocks, star
blocks and comb blocks. Synthetic details on each type of block varies. However, the varied
synthetic details may provide distinctive performance advantages in application. Recently, block
copolymer synthesis has received a greater amount of attention because of controlled radical
polymerizations, mcluding, for example, atom transfer radical polymerization (ATRP), nitroxidemediated
radical polymerization (NMP), and revisible addition fragmentation chain transfer
polymerization (RAFT); See, Braunecker, W. A. et al. Prog. Polym. Sci. 2007, 32, 93. These
new methods provide better control over the block synthesis, as well as synthesis of
novel block copolymers. There are many examples of block copolymer synthesis using
5
controlled radical polymerization in the literature. The most common method for the
preparation of vinyl monomers is the sequential addition of the monomers. This can be
extended if the sequential polymerization is terminated with a functional group such as
alkoxyamine, which can be used as a macroinitiator to prepare a new block. Tenhu et al, reports
the synthesis of A-B-A block copolymers of poly(N-isopropylacrylamide) as a hydrophilic block
and a non-water-soluble-block consisting of poly((3-methoxypropyl)acrylamide) (PMPAM) are
synthesized using RAFT polymerizations. In this reaction, a bifunctional S,S'-bis(a, a'-dimethyla"-
acetic acid)-trithiocarbonate is used as a RAFT agent to obtain the A-B-A block copolymer.
See, Nuopponen et al, J. of Polymer Science, A Poly Chem. 2008, 46, 38. Further,
BlocBuilder®, introduced by Arkema, is a double headed alkoxyamine initiator which will lead to
triblocks. If a single headed initiator is used, the polymer produced will be a simple diblock
copolymer. Blockcopolymers of various composition and morphology will result in polymers
with different properties, which can lead to polymers that behave and perform differently.
[0027] "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,
dimetliylaminoethylacrylate sulfuric acid salt, dimethylaminoethyl acrylate benzyl chloride
quaternary salt (DMAEABCQ) and dimethylaminoethylacrylate methyl sulfate quaternary salt;
the quaternary or acid salts of dialkylaminoalkylacrylamides and methaciylamides 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 ammoniiun chloride (DADMAC). Preferred cationic
monomers include dimethylaminoethylacrylate methyl chloride quaternary salt,
dimethylaminoethyhnethacrylate methyl chloride quaternary salt and diallyldimethyl ammonium
chloride. Diallyldimethyl ammonium chloride is more preferred.
[0028] "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
6
microparticle configuration. Cross linking monomers according to this invention include both
labile cross linking monomers and non-labile cross linking monomers.
[0029] "Emulsion." "microemulsion" and "inverse emulsion" mean a water-in-oil
polymer emulsion comprising a polymeric microparticle according to this invention in the
aqueoijs 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 poljmiers
dispersed within the hydrocarbon matrix. The emulsion polymer are optionally "inverted" or
converted into water-continuous form using shear, dilution, and, generally an inverting
surfactant. See, U.S. Pat. No. 3,734,873, the entire content of \^iuch is incorporated herein by
reference.
[0030] "Fluid mobility" means a ratio that defmes how readily a flxiid moves through a
porous meditim. 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.
[0031] When more than one fluid is flowing the end point relative permeabilities must be
substituted for the absolute permeability used in equation 1.
2. /Lt = — for a fluid x flowing in a porous medium in the presence of one or more
other fluids.
[0032] When two or more fluids are flowmg the fluid mobilities may be used to define a
Mobility ratio
3. M = —= - ^
Xy TJxkry
[0033] 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,
7
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.
[0034] "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.
[0035] "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
trimethactylate, ethoxylated trimethylol triacrylate, ethoxylated pentaerj^thritol 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. Preferred labile
cross linking monomers include water soluble diacrylates such as PEG 200 diacrylate and PEG
400 diacrylate and poljrfimctional vinyl derivatives of a polyalcohol such as ethoxylated (9-20)
trimethylol triacrylate.
[0036] In an embodiment, the labile cross linkers are present in an amount of about 100
to about 200,000 ppm, based on total weight of monomer. In another embodiment, the labile
cross linkers are present in an amount from about 1,000 to about 200,000 ppm. In another
embodiment, the labile cross linkers are present in an amount from about 9,000 to about 200,000
ppm. In another embodiment, the labile cross linkers are present in an amount from about 9,000
to about 100,000 ppm. In another embodiment, the labile cross linkers are present in an amount
from about 20,000 to about 60,000 ppm. In another embodiment, the labile cross linkers are
present in an amount from about 500 to about 50,000 ppm. In another embodiment, the labile
crosslinkers are present in an amount of about 1,000 to about 20,000 ppm.
[0037] "Monomer" means a polymerizable allylic, vinylic or acrylic compound. The
monomer may be anionic, cationic, nonionic or zwitterionic. Vinyl monomers are preferred,
acrylic monomers are more preferred.
[0038] "Nonionic monomer" means a monomer as defined herein which is electrically
neutral. Representative nonionic monomers include N-isopropylacrylamide, N,Ndimethylacrylamide,
N,N-diethyIacrylamide, dimethylaminopropyl acrylamide,
8
dimethylaminopropyl methacrylamide, acryloyl morpholine, hydroxyethyl acrylate,
hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate,
dimethylaminoethylacrylate (DMAEA), dimethylaminoethyl methacrylate (DMAEM), maleic
anhydride, N-vmyl pyrrolidone, vinyl acetate and N-vinyl formamide. Preferred nonionic
monomers include acrylamide, N-methylacrylamide, N,N-dimethylacrylamide and
methacrylamide. Acrylamide is more preferred.
[0039] "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 monomer 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. A preferred non-labile cross linking monomer is methylene bisacrylamide.
[0040] 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
'structure.' Such 'structured' particles can block the pore throats of porous media and create a
blockage of flow.
[0041] 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
9
diameter of the polymeric microparticles is from 0.1 to about 1 microns. In another embodiment,
the unexpanded volume average particle size diameter of the polymeric microparticles is from
about 0.05 to about 50 microns.
[0042] 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.
[0043] In an inverse emulsion or microemulsion process, an aqueous solution of
monomers and cross liiikers is added to a hydrocarbon liquid containing an ^propriate surfactant
or surfactant mixture to form an inverse monomer microemulsion consisthig of small aqueous
droplets dispersed in the continuous hydrocarbon liquid phase and subjecting the monomer
microemulsion to free radical polymerization.
[0044] In addition to the monomers and cross linkers, the aqueous solution may also
contain other conventional additives including chelating agents to remove polymerization
mhibitors, pH adjusters, initiators and other conventional additives.
[0045] 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, ftiel oil, kerosene, odorless mineral spirits
and mixtures of any of the foregoing.
[0046] Surfactants useftil 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.
[0047] 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-bxityl
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
[0048] Alternatively, the polymeric microparticles cross linked with labile cross links are
prepared 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.
10
5,589,525) for water removal. For example, a polymer microparticle prepared from inverse
emulsion polymerization process usir^ 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.
[0049] 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.
[0050] An aqueous suspension of the polymeric microparticles is prepared by
redispersing the dry polymer in water.
[0051] Upon injection into a subterranean formation, the polymeric microparticles flow
through the a 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,
[0052] 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 &om the injection point until it
encounters the high temperature zone.
[0053] Also, the polymeric microparticles of this invention, due to their highly
crosslinked nature, do not expand in solutions of different salinity. Consequently, the viscosity
of the dispersion is not affected by the salinity of the fluid encountered in the subterranean
formation. Accordingly, no special carrier fluid is needed for treatment. Only after the particles
encounter conditions sufficient to reduce the crosslinking density, is the fluid rheology changed
to achieve the desired effect
[0054] Among other factors, the reduction in crosslinking density is dependent on the rate
of cleavage of the labile crosslinker. In particular, 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, when the labile crosslinker is PEG
diacrylate, hydrolysis of the ester linkage is the mechanism of de-crosslihking. Different
alcohols have slightly different rates of hydrolysis. In general, methacrylate esters will hydrolyze
at a slower rate than acrylate esters under similar conditions. With divinyl or diallyl compounds
separated by an azo group such as the diallylamide of 2,2'-Azobis(isbutyric acid), the mechanism
of de-crosslinking is elimination of a nitrogen molecule. As demonstrated by various azo
11
initiators for free radical polymerization, different azo compounds indeed have different half-life
temperatures for decomposition.
[0055] 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 labile crosslinker,
both temperature- and time-dependent expansion properties can be incorporated into the
polymer particles.
[0056] 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.
[0057] An aspect of the present disclosure is to demonstrate the benefits that result fiom
the use of expandable polymeric microparticles having a block copolymer structures. Block
copolymers of various composition and morphology will result in polymers with different
properties and behavior that will aid in improving recovery of hydrocarbon fluids from
subterranean formations. For example, application of a composition of expandable polymeric
microparticles having a block copolymer structure may improve properties including, but not
limited to, the binding, diffusion and rate of expansion of the polymeric microparticles.
[0058] In an embodiment, a composition is provided that includes highly cross linked
expandable poljoneric microparticles having unexpanded volume average particle size diameters
of about 0.05 to about 5,000 microns and cross linking agent contents of about 100 to about
200,000 ppm of labile cross linkers and from 0 to about 300 ppm of non-labile cross linkers,
wherein the expandable polymeric microparticles have a block copolymer structure having at
least two different monomers having different chemical structures. The block copolymer
structure may be any block copolymer structure known in the art. For example, the block
copolymer structure may include segmented blocks, random blocks, di-blocks, tri-blocks,
alternating blocks, periodic blocks, amphiphilic blocks, statistical blocks, star blocks, comb
12
blocks and combinations thereof. In an embodiment, the block copolymer includes a hydrophilic
block of poly(N-isopropylacrylamide) and a non-water-soluble block of poly((3-
methoxypropyl)acrylamide).
[0059] The expandable polymeric microparticles having the block copolymer structure
may be synthesized by any method known in the art. For example, the expandable polymeric
microparticles having the block copolymer structure may be synthesized by methods including,
but not limited to, controlled radical polymerization, anionic polymerization, cationic
polymerization, group transfer polymerization, olefin metathesis polymerization, postpolymerization
formation of metal complexes, and transition metal-catalyzed polymerization. In
an embodiment, the expandable polymeric microparticles having the block copolymer structure is
synthesized by controlled radical polymerization.
[0060] In an embodiment where the expandable polymeric microparticles having the
block copolymer structure are synthesized by controlled radical polymerization, the controlled
radical polymerization technique may be any controlled radical polymerization technique known
in the art For example, the controlled radical polymerization technique may include, but is not
limited to, atom transfer radical polymerization (ATRP), nitroxide-mediated radical
polymerization (NMP), and reversible addition fragmentation chain transfer polymerization
(RAFT).
[0061] Because an embodiment of the present disclosure comprises a composition of at
least two different monomers having different chemical structures, the at least two different
monomers may have any number of characteristics that differ from each other. For example, the
monomers may have different molecular weights, hydrophobicity or hydrophilicity. Differences
in the chemical structures and, therefore, the inherent properties of the different monomers allow
for an improved behavior of the polymeric microparticles with respect to, for example, binding
properties, diffusivity and the rate of expansion of the microparticles within the subterranean
formation.
[0062] The block copolymer structure of the polymeric microparticles in accordance with
present disclosure may include any number of different monomer units. For example, in an
embodiment, the block copolymer may include at least two different monomers, each of which
have different chemical structures. Alternatively, in an embodiment, the block copolymer may
also include a third monomer having a structure that is different from both of the at least two
different monomers. The third monomer may be any monomer known in the art and may be
selected based on the desired properties of the block copolymer. For example, a third monomer
may be selected for its ability to modify the hydrophobicity or the hydrophilicity of the block
13
copolymer. Further, a third monomer may also be selected for its ability to either strengthen or
assist in degrading the backbone of the polymer chain. Accordingly, the skilled artisan will
appreciate that any number of different monomers may be used to synthesize the block
copolymer structure of the polymeric microparticles.
[0063] The unexpanded polymeric microparticles may have any average particle size
diameter useful in appUcations to improve recovery of hydrocarbon fluids from subterranean
formations. For ejcample, the unexpanded polymeric microparticles may have an average particle
size diameter from about 0.05 to about 5,000 microns. In an embodiment, the unexpanded
polymeric microparticles have an average particle size diameter from about 0,1 to about 5
microns. In an embodunent, the unexpanded polymeric microparticles have an average particle
size diameter from about 0.1 to about 3 microns. In another embodiment, the unexpanded
polymeric microparticles have an average particle size diameter from about 0.1 to about 1
micron. In another embodiment, the unexpanded polymeric microparticles have an average
particle size diameter from about 0.05 to about 50 microns.
[0064] In an embodiment, the labile cross Unker is selected from diacrylates and
polyfimctional vinyl derivatives of a polyalcohol. The labile cross-linker may also be
polymethyleneglycol diacrylate.
[0065] In an embodiment, the composition includes cross linked anionic, amphoteric,
ion-pair or betaine-containing polymeric microparticles.
[0066] In an embodiment, the composition is in the form of an emulsion or aqueous
suspension.
[0067] 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.
[0068] In an embodiment, the non-labile cross linker is methylene bisacrylamide.
[0069] 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.
[0070] 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
14
subterranean formation any of the compositions previously described herein, as well as variations
or combinations thereof.
[0071] For example, in an embodiment, a method for improving recovery of hydrocarbon
fluids from a subterranean formation is provided. The method mcludes injecting into a
subterranean formation highly cross linked expandable polymeric microparticles having
unexpanded volume average particle size diameters of about 0.05 to about 5,000 microns and
cross linking agent contents of about 100 to about 200,000 ppm of labile cross linkers and from 0
to about 300 ppm of non-labile cross linkers, wherein the expandable polymeric microparticles
have a block copolymer structure comprising at least two different monomers having different
chemical structures. The microparticles may have a smaller diameter than the pores of the
subterranean formation and the labile cross linkers may break under the conditions of
temperature and pH in the subterranean formation to form expanded microparticles.
[0072] In an embodiment, the highly cross Imked expandable polymeric microparticles
are 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.
[0073] The composition of polymeric microparticles having a block copolymer structure
may be added to the injection water in any amount, based on polymer actives, effective to
improve recovery of hydrocarbon flxxids 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.
[0074] In an embodiment, the injection into the subterranean formation of the highly
cross linked expandable polymeric microparticles is used in a carbon dioxide and water tertiary
recovery project.
[0075] In an embodiment, the injection into the subterranean formation of the highly
cross linked expandable polj^meric microparticles is used in a tertiary oil recovery process, one
component of which constitutes water injection.
[0076] In an embodiment, the subterranean formation is a sandstone or carbonate
hydrocarbon reservoir.
15
[0077] 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
[0078] Preparation of the Polymeric Microparticle
[0079] The polymeric microparticle of the present disclosure may be readily prepared
using inverse emulsion polymerization techniques as described below.
[0080] A representative emulsion polymer composition can be prepared in numerous
ways by the sIdUed artisan. By way of example, a preparation method using (3-
vinylphenyl)azomethylmalonodinitrile is provided herein. A representative emulsion polymer
composition is prepared by polymerizing a monomer emulsion consisting of an aqueous mixture
of 98.94 g of 50% acrylamide, 150 g of 58% sodium acrylamido methylpropane sulfonate
(AMPS), 19.38 g water, 0.5 g 40% pentasodium diethylenetriaminepentaacetate, 0.2 g of (3-
vinylphenyl)azomethylmalonodinitrile, and 36.24 g polyethyleneglycol (PEG) diacrylate as the
dispersed phase and a mixture of 336 g petroleum distillate, 60 g ethoxylated sorbitol oleate and
4 g sorbitan sesquioleate as the continuous phase.
[0081] The monomer emulsion is prepared by mixing the aqueous phase and the oil
phase, followed by homogenization using a Silverson Homogenizer. After deoxygenation with
nitrogen for 30 minutes, poljmierization is initiated by using redox initiators and kept under 35
"C. Once all of the monomer is polymerized, a second batch of monomers: 65.96 g of 50%
acrylamide, 225 g of 58% sodium acrylamido methylpropane sulfonate (AMPS) is added to the
reaction mixture. The reaction is slowly heated to 65 °C and held at that temperature until the
monomer is converted to 50%. The temperature is then raised to 80 "C and held there until all of
the monomer is converted.
[0082] If desired, the polymeric microparticle can be isolated fixDm the latex by
precipitating, filtering, and washing with a mixture of acetone and isopropanol. After drying, the
oil and surfactant free particle can be redispersed in aqueous media.
EXAMPLE 2
[0083] Sand Pack Test
[0084] 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.
16
[0085] 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.
[0086] 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.
[0087] 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.
[0088] This experiment clearly demonstrates two aspects of the invention which are:
[0089] 1. The polymeric microparticles with a conformation constrained by the
built-in reversible crosslinks can be propagated through a porous media.
[0090] 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 3
[0091] Activation of the Polymeric Microparticles by Heat
[0092] As the particles expand in a medium of fixed volume, the volume firaction
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.
[0093] 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
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.
17
[0094] The bottles are placed in a constant temperature oven to age. Then, at a
predetermined time, a bottle can be removed fix)m the oven and cooled to 75oF. The viscosity is
measured at 75 T using Brookfield LV No.l spindle at 60 rpm (shear rate 13.2 sec"').
[0095] Activation of the polymeric microparticles by heat can be demonstrated by
monitoring the viscosity change of aqueous dispersions of particles aged at different temperature.
[0096] 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.
18

CLAIMS
The invention is claimed as follows:
1. A composition comprising:
highly cross linked expandable polymeric microparticles comprising unexpanded volume
average particle size diameters of about 0.05 to about 5,000 microns and cross linking agent
contents of about 100 to about 200,000 ppm of labile cross linkers and from 0 to about 300 ppm
of non-labile cross linkers, wherein the expandable polymeric microparticles have a block
copolymer structure comprising at least two different monomers having different chemical
structures.
2. The composition of Claim 1, wherein the block copolymer structure is selected
from the group consisting of segmented blocks, random blocks, di-blocks, tri-blocks, alternating
blocks, periodic blocks, amphiphilic blocks, statistical blocks, star blocks, comb blocks, and
combinations thereof.
3. The composition of Claim 1, wherein the block copolymer structure comprises a
third monomer having a structure that is different from the structures of the at least two different
monomers.
4. The composition of Claim 1, wherein the expandable polymeric microparticles
having the block copolymer structure are synthesized using a controlled radical polymerization
technique selected from the group consisting of atom transfer radical poljonerization, nitroxidemediated
radical polymerization, reversible addition fragmentation chain transfer polymerization,
and combinations thereof.
5. The composition of Claim 1, wherein the block copolymer structure comprises a
hydrophilic block of poly(N-isopropylacrylamide) and a non-water-soluble block of poly((3-
methoxypropyl)acrylamide).
6. The composition of Claim 1, wherein the unexpanded volume average particle
size diameter is from about 0.1 to about 3 microns.
7. The composition of Claim 1, wherein the unexpanded volume average particle
size diameter is from about 0.1 to about 1 micron.
19
8. The composition of Claim 1, wherein the labile cross linker is selected from
diacrylates and polyfunctional vinyl derivatives of apolyalcohol.
9. The composition of Claim 1, comprising cross linked anionic, amphoteric, ionpair
or betaine-containing polymeric microparticles.
10. The composition of Claim 10, wherein the composition is in the form of an
emulsion or aqueous suspension.
11. The composition of Claim 11, wherein at least one of the cross linked polymeric
microparticles is anionic.
12. The composition of Claim 12, wherein the anionic polymesric 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.
13. The composition of Claim 13, wherein the nonionic monomer is acrylamide and
the anionic monomer is 2-acrylamido-2-methyl-l-propanesulfonic acid.
14. The composition of Claim 13, wherein the labile cross-linker is
polymethyleneglycol diacrylate and the non-labile cross linker is methylene bisacrylamide.
15. A method for improving recovery of hydrocarbon fluids fix)m a subterranean
formation comprising injecting into the subterranean formation a composition comprising highly
cross linked expandable polymeric microparticles comprising according to claim 1, wherein the
microparticles have a smaller diameter than the pores of the subterranean formation and wherein
the labile cross linkers break under the conditions of temperature and pH in the subterranean
formation to form expanded microparticles.
16. The method of Claim 15, vsiierein from about 100 ppm to about 10,000 ppm of the
composition, based on polymer actives, is added to the subterranean formation.
20
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.
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.
21
21. A composition substantially as herein described with reference to the foregoing description and the
accempanying examples. /Dated this 1st day of November 2010. / / /
' ^ v Sfiarad V^ehra
^ ^ ijfKAN Af^KRISHME
REGISTEREj/PATENT AGENT
To -^
The Controller of Patents
The Patent Office
Delhi

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=6CNTQtnvBQlPMlz8eCmD0A==&loc=+mN2fYxnTC4l0fUd8W4CAA==

« Previous Patent

Next Patent »

Patent Number

279615

Indian Patent Application Number

7719/DELNP/2010

PG Journal Number

05/2017

Publication Date

03-Feb-2017

Grant Date

27-Jan-2017

Date of Filing

01-Nov-2010

Name of Patentee

NALCO COMPANY

Applicant Address

1601 W. DIEHL ROAD, NAPERVILLE, IL 60563-1198, UNITED STATES OF AMERICA

Inventors:

#	Inventor's Name	Inventor's Address
1	PIOUS KURIAN	2590 ROURKE DR., AURORA, IL 60503, UNITED STATES OF AMERICA
2	WILLIAM H. JOYCE	12 SHEPARD HILL ROAD, NEWTOWN, CT 06470, UNITED STATES OF AMERICA
3	KIN-TAI CHANG	1126 MISTY LAKE DRIVE, SUGAR LAND, TX 77478, UNITED STATES OF AMERICA

PCT International Classification Number

C09K 8/508

PCT International Application Number

PCT/US2009/040884

PCT International Filing date

2009-04-17

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	12/425,047	2009-04-16	U.S.A.
2	61/046,717	2008-04-21	U.S.A.