WO2023211908A1 - Thermal initiators for polymerizations in mineral oil and methods - Google Patents

Abstract

Stabilizers and methods for making stabilizers that include EXXSOL^TM D40 Naphtha dearomatized fluid and/or EXXSOL^TM D100 low aromatic hydrocarbon solvent, and impart acceptable filter ratios to inverted polymer solutions. Methods include contacting one or more monomers and an initiator, such as dimethyl 2,2'-azobis(2-methylpropionate), in a fluid, such as D40 Naphtha dearomatized fluid, for a time and at a temperature effective to form in the fluid a polymer of the one or more monomers. The one or more monomers may include stearylmethacrylate and methacrylic acid. Emulsions and inverted polymer solutions also are provided.

Description

THERMAL INITIATORS FOR POLYMERIZATIONS IN MINERAL OIL AND METHODS

Cross-Reference to Related Applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63/363,680, filed April 27, 2022, and Finnish Patent Application No. 20225532, filed June 15, 2022, which are incorporated herein by reference.

Background

[0002] Polyacrylamide emulsions (EPAMs) are used in a number of applications, such as fluid mobility control agents in enhanced oil recovery (EOR).

[0003] EPAMs may include a stabilizer. A stabilizer, which may include a copolymer, may prevent or reduce the likelihood of coagulation when an EPAM is subjected to one or more processing steps, such as a concentration step, which may convert EPAM to a concentrated EPAM.

[0004] A stabilizer may include a copolymer dispersed and/or dissolved in an oil. A common stabilizer has been prepared via the polymerization of two oil-soluble monomers in ISOPAR™ G low aromatic hydrocarbon (ExxonMobil, USA) (hereinafter “Isopar G”) (CAS# 64742-48-9 and 90622-57-4). This process has been performed on an industrial scale for years, and the resulting stabilizer includes poly(stearylmethacrylate-co-methacrylic acid) having various mole ratios of monomers, such as a 2: 1 mole ratio or 1 : 1 mole ratio (stearylmethacrylate:methacrylic acid). Although this process is widely used, Isopar G is a relatively expensive starting material.

[0005] Less expensive starting materials have been tested, such as EXXSOL™ D40 Naphtha dearomatized fluid (ExxonMobil, USA) (CAS# 64742-48-9 and 64742-47-8) (hereinafter “D40”). Although D40 and the widely -used Isopar G are both mineral oils, the use of D40 has not resulted in an acceptable stabilizer. When stabilizers made with D40 have been incorporated into an EPAM or an EPAM that is concentrated and then inverted in a brine solution, the resulting inverted solutions have not had favorable filter ratios.

[0006] EPAMs are generally inverse emulsions (water-in-oil) in which water droplets containing polymer are suspended in an oil phase. An important attribute of an EPAM or concentrated EPAM is the filter ratio (FR) it achieves when inverted in a brine solution. The filter ratio measures whether or not a brine solution of the EPAM or concentrated EPAM will partially plug a 1.2 micron pore filter. Avoiding or reducing filter plugging is desired, and usually occurs when FR values do not exceed 1.2. This parameter is particularly important when the EPAM is inverted and used in hydrocarbon recovery operations, such as EOR, where the inverted composition must be able to pass through a porous subterranean formation without restricting or plugging it.

[0007] There remains a need for stabilizers that can be produced with relatively less expensive starting materials, and result in inverted polymer solutions having acceptable filter ratios.

Brief Summary

[0008] Provided herein are embodiments of stabilizers and methods for making stabilizers that (i) include D40, EXXSOL™ DI 00 low aromatic hydrocarbon solvent (ExxonMobil, USA) (CAS# 64742-47-8) (hereinafter “D100”), or a combination thereof, and (ii) impart acceptable filter ratios to inverted polymer solutions.

[0009] It has been surprisingly discovered that the use of dimethyl 2,2’-azobis(2- methylpropionate) as an initiator for stabilizer synthesis (which is commercially available as V-601 oil soluble initiator (FUJIFILM® Wako Pure Chemical Corporation, USA)) permits stabilizers that impart acceptable filter ratios to inverted liquid polymer solutions to be produced with relatively inexpensive mineral oils, such as D40 and other mineral oils that include components having a broader range of boiling points than Isopar G. It has been further surprisingly discovered that a stabilizer that is prepared with dimethyl 2,2’-azobis(2- methylpropi onate) as an initiator, and includes D40 or EXXSOL™ DI 00 low aromatic hydrocarbon solvent can be used to form water-in-oil emulsions, as described herein, that have an average brine viscosity that is at least 10 %, at least 15 %, at least 20 %, at least 25 %, or least 30 % greater than comparable water-in-oil emulsions that contain a stabilizer formed wdth an initiator other than dimethyl 2,2’-azobis(2-methylpropionate) and/or does not include D40 or EXXSOL™ D100 low aromatic hydrocarbon.

[0010] In one aspect, methods of producing stabilizers are provided. In some embodiments, the methods include contacting one or more monomers and an initiator in a fluid for a time and at a temperature effective to form in the fluid a polymer including the one or more monomers; wherein the initiator includes dimethyl 2,2’-azobis(2-methylpropionate); and wherein the fluid includes D40, DI 00, or a combination thereof. The one or more monomers may include stearylmethacrylate and methacrylic acid

[0011] In another aspect, methods of forming a water-in-oil emulsion also are provided. In some embodiments, the methods include providing an aqueous phase including acrylamide, a comonomer, a chain transfer agent, a chelating agent, and water; providing an oil phase including a first organic liquid and a stabilizer as described herein; combining the aqueous phase and the oil phase to form the emulsion; and initiating polymerization of the acrylamide and the comonomer to form a copolymer in the emulsion. In some embodiments, the methods of forming an emulsion include providing an aqueous phase that includes acrylamide, a comonomer, a chain transfer agent, a chelating agent, and water; providing an oil phase that includes a first organic liquid; combining the aqueous phase and the oil phase to form the emulsion; initiating polymerization of the acrylamide and the comonomer to form a copolymer in the emulsion; and adding a stabilizer as described herein to the emulsion. The stabilizer may be added after the polymerization is substantially complete. The emulsion may be inverted in a brine to form an inverted polymer solution. The inverted polymer solution may have a filter ratio of less than or equal to 1.2, less than 1.2, less than or equal to 1.1, less than 1.1, less than or equal to 1.05, or less than 1.05, wherein the filter ratio is determined by filtering the inverted polymer solution through a 1.2 pm pore filter with a diameter of 47 mm at 15 psi of N2gas, and ambient temperature (25 °C).

[0012] In one aspect, stabilizers and emulsions are provided herein. In some embodiments, the stabilizers include poly(stearylmethacrylate-co-methacrylic acid), and a fluid including D40, DI 00, or a combination thereof. The poly(stearylmethacrylate-co-methacrylic acid) may be present in the stabilizer at an amount of about 10 % to about 25 %, by weight, based on the weight of the stabilizer. In some embodiments, emulsions are provided in which a stabilizer is present, and the stabilizer may be present at an amount of about 1 % to about 10 %, by weight, based on the weight of the water-in-oil emulsion. The organic liquid of a water-in-oil emulsion may include DI 00, D40, or a combination thereof. The water-in-oil emulsions described herein may be inverted in an aqueous liquid, such as a brine, to form a liquid polymer solution, which may be referred to as an inverted polymer solution. In some embodiments, an inverted polymer solution of the water-in-oil emulsion having a 2,000 ppm concentration of a copolymer formed of acrylamide and a comonomer, (e.g., poly (aery lamide-co-sodium acrylate)) has a filter ratio of less than or equal to 1.2, less than or equal to 1.1, or less than or equal to 1.05, wherein the filter ratio is determined by filtering the inverted polymer solution through a 1.2 pm pore filter with a diameter of 47 mm at 15 psi ofN2gas, and ambient temperature (25 °C).

[0013] In a still further aspect, methods of treating subterranean formations are provided. In some embodiments, the methods include contacting a subterranean formation with an inverted polymer solution described herein. The contacting of the subterranean formation with the inverted polymer solution may be part of a hydrocarbon recovery process, for example, enhanced oil recovery (EOR). [0014] Additional aspects will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the aspects described herein. The advantages described herein may be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive.

Detailed Description

[0015] Provided herein are stabilizers, emulsions, and methods, including methods of producing stabilizers and emulsions, and methods of treating subterranean formations. Methods of Producing Stabilizers

[0016] Methods of producing stabilizers are provided herein. In some embodiments, the methods include contacting one or more monomers and an initiator in a fluid for a time and at a temperature effective to form in the fluid a polymer of the one or more monomers.

[0017] The fluid that includes the polymer of the one or more monomers may be combined with a dilution fluid to form a stabilizer described herein. In some embodiments, the fluid that includes the polymer of the one or more monomers is combined with a dilution fluid and sorbitan monooleate to form a stabilizer described herein. Instead of, or in addition to, sorbitan monooleate, another additive that prevents or reduces gelling over time may be used. Any fluid described herein or known in the art may be used as a dilution fluid. In some embodiments, the dilution fluid includes D40, DI 00, or a combination thereof. When sodium monooleate is present in a stabilizer, the sodium monooleate may be present at an amount of about 1 % to about 3 %, by weight, based on the weight of the stabilizer.

[0018] A polymer of the one or more monomers may be present at any concentration in the stabilizers described herein. An amount of dilution fluid may be selected to achieve a desired polymer concentration. For example, an amount of dilution fluid may be effective to prevent formation of a stabilizer gel. In some embodiments, a polymer of the one or more monomers is present in a stabilizer at an amount of about 10 % to about 25 %, by weight, based on the w eight of the stabilizer, or about 15 % to about 20 %, by weight, based on the weight of the stabilizer.

Initiators

[0019] In some embodiments, the initiator used in the methods described herein includes dimethyl 2,2’-azobis(2-methylpropionate). Commercially available dimethyl 2,2’-azobis(2- methylpropionate) may be used in the methods described herein. For example, the initiator may include V-601 oil soluble initiator (FUJIFILM® Wako Pure Chemical Corporation, USA).

Fluids

[0020] In some embodiments, the fluid used in the methods of producing stabilizers includes D40. In some embodiments, the fluid used in the methods of producing stabilizers includes DI 00. In some embodiments, the fluid used in the methods of producing stabilizers includes D40 and D I 00.

[0021] In some embodiments, the fluid used in the methods of producing stabilizers is a mineral oil that includes components having a broader range of boiling points than those of Isopar G.

[0022] Whenever a composition or method described herein includes or uses D40 and/or DI 00, the D40 and/or DI 00 may be substituted with, or used in addition to, a mineral oil that includes components having a broader range of boiling points than those of Isopar G.

Monomers

[0023] In some embodiments, the one or more monomers include stearylmethacrylate and methacrylic acid.

[0024] As used herein, the term “stearylmethacrylate” refers to and includes stearylmethacrylate and a combination of stearylmethacry late and cetylmethacrylate. Mixtures of stearyl and cetyl methacrylates are commercially available, and commonly marketed at “steary lmethacrylate”.

[0025] When stearylmethacrylate and methacrylic acid are used as the one or more monomers in the methods described herein, any weight or mole ratio of the two monomers may be used in the methods and/or be present in the poly(steary Imethacrylate-co-methacrylic acid) described herein. In some embodiments, the mole ratio of stearylmethacrylate to methacrylic acid in the polymers described herein — e.g., poly(stearylmethacrylate-co- methacrylic acid) — is about 1-3:1, about 1.5-2.5: !, or about 2: 1.

Contacting of Monomers and Initiator

[0026] The contacting of the one or more monomers and the initiator may be achieved with any technique known in the art. In some embodiments, the contacting of the one or more monomers and initiator includes providing a first mixture that includes a first portion of the one or more monomers, a first portion of the initiator, and a first portion of the fluid; providing a second mixture that includes a second portion of the one or more monomers, a second portion of the initiator, and a second portion of the fluid; and contacting the first mixture and the second mixture to form a third mixture. [0027] The “first portion of the one or more monomers” may include one or two types of monomer, and the “second portion of the one or more monomers” may include one or two types of monomer. For example, the first portion of the one or more monomers may consist of stearylmethacrylate, and the second portion of the one or more monomers may include stearylmethacrylate and methacrylic acid. Other possibilities are envisioned.

[0028] In some embodiments, the first mixture includes D40, dimethyl 2,2’-azobis(2- methylpropionate), and stearylmethacrylate. Any weight ratio of these components may be present in the first mixture. For example, a weight ratio of the D40 to the dimethyl 2,2’- azobis(2-methylpropi onate) to the stearylmethacrylate in the first mixture may be (1) about 250-300:0.1-0.6:15-45, (2) about 260-280:0.2-0.5:20-40; or (3) about 265-275:0.2-0.4:25-35. [0029] In some embodiments, the second mixture includes D40, stearylmethacrylate, methacrylic acid, and dimethyl 2,2’-azobis(2-methylpropionate). Any weight ratio of these components may be present in the second mixture. For example, a weight ratio of the D40 to the stearylmethacrylate to the methacrylic acid to the dimethyl 2,2’-azobis(2- methylpropionate) in the second mixture may be (1) about 350-400: 100-150:10-30:0.5-2.5, (2) about 360-380:110-140:0.8 - 2; or (3) about 360-370:125-135: 15-25:1-1.5.

[0030] The contacting of one or more monomers and initiator may occur, in whole or in part, at any temperature effective to achieve a desired degree of polymerization. In some embodiments, the temperature is about 75 °C to about 125 °C, about 80 °C to about 120 °C, about 85 °C to about 95 °C, or about 90 °C.

Methods of Forming Emulsions

[0031] Also provided herein are methods of forming emulsions, such as water-in-oil emulsions. The emulsions generally may be formed by polymerizing one or more monomers in a water-in-oil emulsion, and in the presence of a stabilizer as described herein. In some embodiments, the methods of forming an emulsion include providing an aqueous phase that includes at least one type of monomer, a chain transfer agent, a chelating agent, and water; providing an oil phase that includes a first organic liquid and a stabilizer as described herein; combining the aqueous phase and oil phase; and initiating polymerization of the monomers. The combining of the aqueous phase and oil phase may include homogenizing the aqueous phase and oil phase.

[0032] In some embodiments, the methods of forming an emulsion include providing an aqueous phase that includes acrylamide, a comonomer, a chain transfer agent, a chelating agent, and water; providing an oil phase that includes a first organic liquid and a stabilizer as described herein; combining the aqueous phase and the oil phase to form the emulsion; and initiating polymerization of the acrylamide and the comonomer to form a copolymer in the emulsion.

[0033] In some embodiments, the methods of forming an emulsion include providing an aqueous phase that includes acrylamide, a comonomer, a chain transfer agent, a chelating agent, and water; providing an oil phase that includes a first organic liquid; combining the aqueous phase and the oil phase to form the emulsion; initiating polymerization of the acrylamide and the comonomer to form a copolymer in the emulsion; and adding a stabilizer as described herein to the emulsion. The stabilizer may be added after the polymerization is substantially complete.

[0034] The comonomer generally may include any poly merizable monomer, such as a polymerizable vinylic monomer. The comonomer may include one type of comonomer (e g., an acrylate), or two types of comonomer (e.g., an acrylate and a second, different comonomer, such as acrylamide tertiary butyl sulfonic acid (ATBS)). Therefore, the term “copolymer”, as used herein, refers to polymers formed of at least two different types of monomers, including, but not limited to, terpolymers. The comonomer, in some embodiments, includes acrylic acid or an acrylate. An acrylate may be a salt including any cation, and non-limiting examples of acrylate salts include calcium acrylate, magnesium acrylate, potassium acrylate, sodium acrylate, etc. When the comonomer includes sodium acrylate, the copolymer may be poly(acrylamide-co-sodium acrylate). The comonomer may include any one or more types of monomers described in U.S. Patent Application Publication No. 2020/0165778, which is incorporated by reference herein. For example, the comonomer may be selected from acrylic acid, an acrylate, an acrylic ester, a partially hydrolyzed acrylic ester, methacrylic acid, a methacrylate, a polyacrylamide derivative, such as acrylamide tertiary butyl sulfonic acid (ATBS), an olefin, such as ethylene, propylene, butylene, or oxides thereof, a dibasic acid, an anhydride, such as maleic anhydride, polyvinyl alcohol (PVA), A-vinylpyrrolidone, polystyrene sulfonate, styrene, methylstyrene, alkylene oxides, or any combination thereof. In some embodiments, the comonomer is acrylic acid or an acrylate, such as sodium acrylate. In some embodiments, the comonomer includes (i) acrylic acid or an acrylate, such as sodium acrylate, and (ii) ATBS.

[0035] Any polymerization initiator may be used in the methods of forming a polymer emulsion. The polymerization initiator may include a redox-couple. In some embodiments, the polymerization initiator includes /-butyl hydroperoxide with aqueous SO2.

[0036] Any chain transfer agent may be employed, such as propylene glycol, isopropanol, 2-mercaptoethanol, sodium hypophosphite, dodecyl mercaptan and thiogly colic acid. The chain transfer agent may be present at an amount of about 0. 1 % to 10 %, by weight, based on the weight of an emulsion, but other amounts are envisioned.

[0037] The emulsions provided herein generally may include any amount of water. For example, an emulsion, before the optional concentration process described herein, may include water at an amount of less than or equal to 50 %, less than or equal to 40 %, or less than or equal to 30 %, by weight, based on the weight of the emulsion. In some embodiments, an emulsion, before the optional concentration process described herein, includes water at an amount of about 40 % to about 50 %, or about 40 % to about 45 %, by weight, based on the weight of the emulsion. In some embodiments, an emulsion, before the optional concentration process described herein, includes water at an amount of at least 20 %, by weight, based on the weight of the emulsion.

[0038] For example, an emulsion, after the optional concentration process described herein, may include water at an amount of less than or equal to 12 %, less than or equal to 10 %, or less than or equal to 8 %, by weight, based on the weight of the emulsion. In some embodiments, an emulsion, after the optional concentration process described herein, includes water at an amount of at least 5 %, by weight, based on the weight of the emulsion. [0039] After the optional concentration process described herein, an emulsion may include any polymer concentration. For example, an emulsion, after the optional concentration process described herein, may include a polymer (e.g., a copolymer) at an amount of at least 35 %, at least 40 %, at least 45 %, or at least 50 %, by weight, based on the weight of the emulsion.

[0040] In some embodiments, the aqueous phase includes isopropanol, pentasodium diethylenetriaminepentaacetate, or a combination thereof. After polymerization, sodium metabisulfite may be added. Instead of, or in addition to, sodium metabisulfite, another agent may be added that is capable of reacting with unreacted monomer.

[0041] In some embodiments, the methods of forming an emulsion include modifying a pH of the aqueous phase prior to the combining of the aqueous phase and the oil phase. The modifying of the pH of the aqueous phase may be achieved using any known technique. In some embodiments, the modifying of the pH of the aqueous phase comprises contacting the aqueous phase with a base, such as sodium hydroxide. After the modifying of the pH, the aqueous phase may have a modified pH of about 6 to about 7, or about 6 to about 6.8, or about 6.5 to about 6.8. In some embodiments, the first organic liquid of the oil phase includes DI 00, D40, or a combination thereof. When DI 00 and D40 are present in an oil, any ratio of two liquids may be present. In some embodiments, a weight ratio of DI 00 to D40 in the oil phase is about 150-175:15-30.

[0042] In some embodiments, the methods include contacting the emulsion with sodium metabisulfite after the poly merization is substantially complete.

[0043] In some embodiments, the methods include contacting an emulsion as described herein with an inverting surfactant, such as after the polymerization is substantially complete. An inverting surfactant generally may be present at any effective concentration. In some embodiments, an inverting surfactant is present at any amount of about 1 % to about 10 %, about 1 % to about 8 %, about 1 % to about 5 %, or about 2 % to about 4 %, by weight, based on the weight of an emulsion. Any inverting surfactant known in the art may be used. Nonlimiting examples of surfactants, including inverting surfactants, that may be used in the compositions and methods herein are described in U.S. Patent Application Publication No. 2019/0241793, which is incorporated herein by reference.

[0044] It is known in the art to describe the capability of surfactants to stabilize water-in- oil-emulsions or oil-in-water emulsions by using the so called “HLB-value” (hydrophilic- lipophilic balance). The HLB-value usually is a number from 0 to 20. In surfactants having a low HLB-value, the lipophilic parts of the molecule predominate and consequently such surfactants are usually good water-in-oil emulsifiers. In surfactants having a high HLB-value, the hydrophilic parts of the molecule predominate, and consequently such surfactants are usually good oil-in-water emulsifiers.

[0045] As a result, emulsifying surfactants typically are surfactants having an HLB-value of about 2 to less than 10, and inverting surfactants are surfactants having an HLB-value of about 10 to about 20.

[0046] Exemplary inverting surfactants include, but are not limited to, ethoxylated alcohols, alcohol ethoxylates, ethoxylated esters of sorbitan, ethoxylated esters of fatty acids, ethoxylated fatty acid esters, and ethoxylated esters of sorbitol and fatty acids, or any combination thereof. Exemplary inverting surfactants include nonionic surfactants that include a hydrocarbon group and a polyalkylenoxy group of sufficient hydrophilic nature. Nonionic surfactants of the general formula R¹ — O — (CH(R²) — CH2 — O)_nH (I) may be used, wherein R¹ is a C8-C22-hydrocarbon group, preferably an aliphatic Cio-Cis-hydrocarbon group, n is a number of > 4, preferably > 6, and R² is H, methyl or ethyl with the proviso that at least 50 % of the groups R² are H. Examples of such surfactants include poly ethoxylates based on Cio-Cis-alcohols such as C12/14-, C14/18- or Ci6/i8-fatty alcohols, CB — or C13/15- oxoalcohols. The HLB-value of the inverting surfactant may be adjusted by selecting the number of ethoxy groups. Specific examples include tridecylalcohol ethoxylates comprising from 4 to 14 ethylenoxy groups, e.g. tridecyalcohol-8 EO or C 12/14 fatty alcohol ethoxylates, e.g. C12/14 • 8 EO. Examples of inverting surfactants also include modified polyester surfactants, anhydride substituted ethylene copolymers, V,JV-dialkanol substituted fatty amides, and tallow amine ethoxylates. Further exemplary inverting surfactants comprise include anionic surfactants, for example surfactants comprising phosphate or phosphonic acid groups.

[0047] The emulsions produced by the methods described herein may be concentrated. Any concentration process known in the art may be used. In some embodiments, the methods described herein include, after polymerization is substantially complete, optionally contacting the emulsion with a second organic liquid; reducing a volume of the emulsion; and optionally contacting the emulsion with an amount of inverting surfactant. The second organic liquid may include D40. The reducing of the volume of the emulsion may be achieved using any known technique, including, but not limited to, distillation. Contacting the emulsion with the second organic liquid may be optional, because doing so may not be necessary' if a sufficient amount of the first organic liquid is present in the oil phase used to form the emulsion. The first organic liquid and the second organic liquid may be the same or different.

[0048] The methods provided herein may include inverting an emulsion described herein in water or a brine to form an inverted polymer solution. The methods also may include diluting the inverted polymer solution to achieve a target concentration of a copolymer formed of acrylamide and a comonomer (e.g., poly(acrylamide-co-sodium acrylate)). The target concentration may be about 1,000 ppm to about 5,000 ppm, or about 1,000 ppm to about 3,000 ppm, or about 1,500 ppm to about 2,500 ppm. In some embodiments, the target concentration is about 2,000 ppm.

[0049] The inverted polymer solutions described herein, including those having a target concentration of a copolymer of 2,000 ppm, may have a filter ratio of less than or equal to 1.2, less than or equal to 1.1, or less than or equal to 1.05, wherein the filter ratio, as described herein, is determined by filtering the inverted polymer solution through a 1.2 pm pore filter with a diameter of 47 mm at 15 psi of N2 gas, and ambient temperature (25 °C). Stabilizers, Emulsions, and Inverted Polymer Solutions

[0050] In one aspect, stabilizers are provided herein. In some embodiments, the stabilizers include poly(stearylmethacrylate-co-methacrylic acid), and a fluid comprising D40. [0051] In some embodiments, the stabilizers include poly(stearylmethacrylate-co- methacrylic acid) and a mineral oil that includes components having a broader range of boiling points than those of Isopar G.

[0052] A mole ratio of stearylmethacrylate monomer to methacrylic acid monomer in the poly (stcaryhncthacrylate-co-mcthacry lie acid) may be about 1-3: 1, or about

[0053] 2:1. In some embodiments, the stabilizers include sodium monooleate, which may be present at an amount of about I % to about 3 %, by weight, based on the weight of the stabilizer. The poly(stearylmethacrylate-co-methacrylic acid) may be present in the stabilizer at an amount of about 10 % to about 25 %, by weight, based on the weight of the stabilizer, or about 15 % to about 20 %, by weight, based on the weight of the stabilizer.

[0054] Any of the stabilizers provided herein may be a component of an emulsion described herein, such as a water-in-oil emulsion. The water-in-oil emulsions provided herein may include a stabilizer as described herein, a copolymer formed of acrylamide and a comonomer (e.g., poly(acrylamide-co-sodium acrylate)), water, and an organic liquid. The stabilizer may be present in a water-in-oil emulsion at any amount. In some embodiments, a stabilizer is present at an amount of about 1 % to about 10 %, about 1 % to about 9.8 %, or about 1 % to about 8 %, by weight, based on the weight of the water-in-oil emulsion. The organic liquid of a water-in-oil emulsion may include DI 00, D40, or a combination thereof. The weight ratio of D100 to D40 in the water-in-oil emulsion may be about 150-175: 15-30. [0055] The water-in-oil emulsions described herein may be inverted in an aqueous liquid, such as a brine, to form a liquid polymer solution, which may be referred to as an inverted polymer solution. The brine may be a synthetic brine. In some embodiments, an inverted polymer solution of the water-in-oil emulsion having a 2,000 ppm concentration of a copolymer formed of acrylamide and a comonomer (e.g., poly(acrylamide-co-sodium acrylate)) has a filter ratio of less than or equal to 1.2, less than or equal to 1.1, or less than or equal to 1.05, wherein the filter ratio is determined by filtering the inverted polymer solution through a 1.2 pm pore filter with a diameter of 47 mm at 15 psi of N2 gas, and ambient temperature (25 °C).

Method of Treating Subterranean Formations

[0056] Also provided herein are methods of treating a subterranean formation. The methods may include contacting a subterranean formation with any of the inverted polymer solutions described herein. Any subterranean formation may be treated with the methods described herein. In some embodiments, the subterranean formation is ahydrocarbon- containing formation. [0057] In some embodiments, the contacting of a subterranean formation with an inverted polymer solution is part of a hydrocarbon recovery process, for example, EOR. Examples of EOR applications are described in WO 2018/045282, which is incorporated by reference herein.

[0058] As used herein, the phrase "enhanced oil recovery" (i.e., "EOR") (also known as tertiary mineral oil production) refers to a process for mineral oil production in which an aqueous injection fluid comprising at least a water soluble polymer is injected into a mineral oil deposit. The techniques of tertiary mineral oil production include what is known as "polymer flooding". Polymer flooding includes injecting an aqueous solution of a water- soluble thickening polymer through the injection boreholes into the mineral oil deposit. As a result of the injection of the polymer solution, the mineral oil may be forced through the cavities in the formation, proceeding from the injection borehole, in the direction of the production borehole, and the mineral oil may be produced through the production borehole. By virtue of the fact that the polymer formulation has an increased viscosity compared to the viscosity of water, the risk that the polymer formulation breaks through to the production borehole can be reduced. It is thus possible to mobilize additional mineral oil in the formation. Details of polymer flooding and of polymers suitable for this purpose are disclosed, for example, in "Petroleum, Enhanced Oil Recovery, Kirk-Othmer, Encyclopedia of Chemical Technology, online edition, John Wiley & Sons, 2010". For polymer flooding, a multitude of different water-soluble thickening polymers may be used, especially high molecular weight polyacrylamide, copolymers of acry lamide and further comonomers, for example vinylsulfonic acid or acrylic acid. Polyacrylamide may be partly hydrolyzed polyacrylamide, in which some of the acrylamide units have been hydrolyzed to acrylic acid. It is known in the art to use inverse emulsions of polyacry lamide (co)polymers for enhanced oil recovery (EOR) in particular for use on off-shore platforms. Such inverse emulsions ty pically comprise about 30 wt. % of polymers. For use, inverse emulsions are simply diluted with water to the final concentration of the polymer.

[0059] All referenced publications are incorporated herein by reference in their entirety. Furthermore, where a definition or use of a term in a reference, which is incorporated by reference herein, is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

[0060] While certain aspects of conventional technologies have been discussed to facilitate disclosure of various embodiments, applicants in no way disclaim these technical aspects, and it is contemplated that the present disclosure may encompass one or more of the conventional technical aspects discussed herein.

[0061] The present disclosure may address one or more of the problems and deficiencies of known methods and processes. However, it is contemplated that various embodiments may prove useful in addressing other problems and deficiencies in a number of technical areas. Therefore, the present disclosure should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein.

[0062] In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge, or otherwise constitutes prior art under the applicable statutory provisions; or is known to be relevant to an attempt to solve any problem with which this specification is concerned.

[0063] In the descriptions provided herein, the terms “includes,” “is,” “containing,” “having,” and “comprises” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” When stabilizers, emulsions, or methods are claimed or described in terms of “comprising” various steps or components, the stabilizers, emulsion, or methods can also “consist essentially of’ or “consist of’ the various steps or components, unless stated otherwise.

[0064] The terms “a,” “an,” and “the” are intended to include plural alternatives, e.g., at least one. For instance, the disclosure of “a monomer”, “an organic liquid”, and the like, is meant to encompass one, or mixtures or combinations of more than one monomer, organic liquid, and the like, unless otherwise specified.

[0065] Various numerical ranges may be disclosed herein. When Applicant discloses or claims a range of any type, Applicant’s intent is to disclose or claim individually each possible number that such a range could reasonably encompass, including end points of the range as well as any sub-ranges and combinations of sub-ranges encompassed therein, unless otherwise specified. Moreover, all numerical end points of ranges disclosed herein are approximate. As a representative example. Applicant discloses, in some embodiments, that the polymer is present in the stabilizer at an amount of about 15 % to about 20 %, by weight, based on the weight of the stabilizer. This range should be interpreted as encompassing about 15 % and about 20 %, and further encompasses “about” each of 16 %, 17 %, 18 %, and 19 %, including any ranges and sub-ranges between any of these values. [0066] As used herein, the term “about” means plus or minus 10 % of the numerical value of the number with which it is being used.

EMBODIMENTS

[0067] The following is a non-limiting list of embodiments:

[0068] Embodiment 1. A method of producing a stabilizer, the method comprising contacting one or more monomers and an initiator in a fluid for a time and at a temperature effective to form in the fluid a polymer of the one or more monomers; wherein the initiator comprises dimethyl 2,2 ’-azobis(2-methylpropi onate); and wherein the fluid comprises EXXSOL™ D40 Naphtha dearomatized fluid, EXXSOL™ DI 00 low aromatic hydrocarbon solvent, or a combination thereof.

[0069] Embodiment 2. The method of Embodiment 1, wherein the one or more monomers comprise stearylmethacrylate and methacrylic acid.

[0070] Embodiment 3. The method of Embodiment 1 or 2, wherein the contacting of the one or more monomers and the initiator comprises providing a first mixture comprising a first portion of the one or more monomers, a first portion of the initiator, and a first portion of the fluid; providing a second mixture comprising a second portion of the one or more monomers, a second portion of the initiator, and a second portion of the fluid; and contacting the first mixture and the second mixture to form a third mixture.

[0071] Embodiment 4. The method of Embodiment 3, wherein the first portion of the one or more monomers consists of stearylmethacrylate, and the second portion of the one or more monomers comprises stearylmethacrylate and methacrylic acid.

[0072] Embodiment 5. The method of Embodiment 4, wherein a weight ratio of the EXXSOL™ D40 Naphtha dearomatized fluid to the dimethyl 2,2’-azobis(2- methylpropionate) to the stearylmethacrylate in the first mixture is about 250-300:0.1-0.6:15- 45.

[0073] Embodiment 6. The method of Embodiment 4, wherein a weight ratio of the EXXSOL™ D40 Naphtha dearomatized fluid to the dimethyl 2,2’-azobis(2- methylpropionate) to the stearylmethacrylate in the first mixture is about 265-275:0.2-0.4:25- 35.

[0074] Embodiment 7. The method of any one of Embodiment 4 to 6, wherein a weight ratio of the EXXSOL™ D40 Naphtha dearomatized fluid to the stearylmethacrylate to the methacrylic acid to the dimethyl 2,2’ -azobis(2-methylpropi onate) in the second mixture is about 350-400:100-150: 10-30:0.5-2.5. [0075] Embodiment 8. The method of any one of Embodiments 4 to 6, wherein a weight ratio of the EXXSOL™ D40 Naphtha dearomatized fluid to the stearylmethacrylate to the methacrylic acid to the dimethyl 2,2’ -azobis(2-methylpropi onate) in the second mixture is about 360-370:125-135: 15-25:1-1.5.

[0076] Embodiment 9. The method of any one of Embodiments 2 to 8, wherein a mole ratio of stearylmethacrylate to methacrylic acid in the polymer is about 1-3: 1.

[0077] Embodiment 10. The method of any one of Embodiments 2 to 8, wherein a mole ratio of stearylmethacrylate to methacrylic acid in the polymer is about 2: 1.

[0078] Embodiment 11. The method of any one of the preceding Embodiments, wherein the temperature is about 80 °C to about 120 °C.

[0079] Embodiment 12. The method of any one of the preceding Embodiments, wherein the temperature is about 85 °C to about 95 °C.

[0080] Embodiment 13. The method of any one of the preceding Embodiments, further comprising combining the fluid comprising the polymer with a dilution fluid and optionally sorbitan monooleate to form the stabilizer.

[0081] Embodiment 14. The method of Embodiment 13, wherein the polymer is present in the stabilizer at an amount of about 10 % to about 25 %, by weight, based on the weight of the stabilizer.

[0082] Embodiment 15. The method of Embodiment 13, wherein the polymer is present in the stabilizer at an amount of about 15 % to about 20 %, by weight, based on the weight of the stabilizer

[0083] Embodiment 16. The method of any one of Embodiments 13 to 15, wherein the sorbitan monooleate is present in the stabilizer at an amount of about 1 % to about 3 %, by weight, based on the weight of the stabilizer.

[0084] Embodiment 17. The method of any one of Embodiments 13 to 16, wherein the dilution fluid comprises EXXSOL™ D40 Naphtha dearomatized fluid, EXXSOL™ D100 low aromatic hydrocarbon solvent, or a combination thereof.

[0085] Embodiment 18. A method of forming an emulsion, the method comprising:

[0086] (A) providing an aqueous phase comprising acrylamide, a comonomer, a chain transfer agent, a chelating agent, and water; providing an oil phase comprising a first organic liquid and the stabilizer of any one of Embodiments 13 to 17 or 38 to 44; combining the aqueous phase and the oil phase to form the emulsion; and initiating polymerization of the acrylamide and the comonomer with a polymerization initiator to form a copolymer in the emulsion; wherein, optionally, the oil phase further comprises an emulsifier; or [0087] (B) providing an aqueous phase that includes acrylamide, a comonomer, a chain transfer agent, a chelating agent, and water; providing an oil phase that includes a first organic liquid; combining the aqueous phase and the oil phase to form the emulsion; initiating polymerization of the acrylamide and the comonomer to form a copolymer in the emulsion; and adding the stabilizer of any one of Embodiments 13 to 17 or 38 to 44 to the emulsion; wherein, optionally, the oil phase further comprises an emulsifier.

[0088] Embodiment 19. The method of Embodiment 18, wherein the polymerization initiator comprises /-butyl hydroperoxide and aqueous SO2.

[0089] Embodiment 20, The method of Embodiment 18 or 19, wherein the aqueous phase further comprises isopropanol, pentasodium diethylenetriaminepentaacetate, or a combination thereof.

[0090] Embodiment 21. The method of any one of Embodiments 18 to 20, further comprising modifying a pH of the aqueous phase prior to the combining of the aqueous phase and the oil phase.

[0091] Embodiment 22. The method of Embodiment 21, wherein the modifying of the pH of the aqueous phase comprises contacting the aqueous phase with a base, such as sodium hydroxide.

[0092] Embodiment 23. The method of Embodiment 21 or 22, wherein after the modifying of the pH, the aqueous phase has a modified pH of about 6 to about 7.

[0093] Embodiment 24. The method of any one of Embodiments 18 to 23, wherein the first organic liquid comprises EXXSOE™ DI 00 low aromatic hydrocarbon solvent, EXXSOL™ D40 Naphtha dearomatized fluid, or a combination thereof.

[0094] Embodiment 25. The method of Embodiment 24, wherein a weight ratio

EXXSOL™ DI 00 low aromatic hydrocarbon solvent to EXXSOL™ D40 Naphtha dearomatized fluid in the oil phase is about 150-175:15-30.

[0095] Embodiment 26. The method of Embodiment 24, wherein a weight ratio

EXXSOL™ DI 00 low aromatic hydrocarbon solvent to EXXSOL™ D40 Naphtha dearomatized fluid in the oil phase is about 165:20.

[0096] Embodiment 27. The method of any one of Embodiments 18 to 26, wherein the combining of the aqueous phase and the oil phase comprises homogenizing the aqueous phase and the oil phase.

[0097] Embodiment 28. The method of any one of Embodiments 18 to 27, wherein the comonomer (i) comprises acrylic acid or an acrylate, such as calcium acrylate, potassium acrylate, sodium acrylate, or magnesium acrylate, (ii) is selected from acrylic acid, an acrylate, such as calcium acrylate, potassium acrylate, sodium acrylate, or magnesium acrylate, an acrylic ester, a partially hydrolyzed acrylic ester, methacrylic acid, a methacrylate, a polyacrylamide derivative, such as acrylamide tertiary butyl sulfonic acid (ATBS), an olefin, such as ethylene, propylene, butylene, or oxides thereof, a dibasic acid, an anhydride, such as maleic anhydride, polyvinyl alcohol (PVA), A-vinylpyrrolidone, polystyrene sulfonate, styrene, methylstyrene, alkylene oxides, or any combination thereof, or (iii) includes (a) acrylic acid or an acrylate, such as sodium acrylate, and (b) ATBS.

[0098] Embodiment 29. The method of any one of Embodiments 18 to 27, further comprising, after the polymerization is substantially complete, contacting the emulsion with an agent that is capable of reacting with unreacted monomer, such as sodium bisulfite.

[0099] Embodiment 30. The method of any one of Embodiments 18 to 29, further comprising, after the polymerization is substantially complete, contacting the emulsion with an inverting surfactant.

[0100] Embodiment 31. The method of any one of Embodiments 18 to 29, further comprising, after the polymerization is substantially complete: optionally contacting the emulsion with a second organic liquid; reducing a volume of the emulsion; and optionally contacting the emulsion with an amount of inverting surfactant.

[0101] Embodiment 32. The method of Embodiment 31, wherein the second organic liquid comprises EXXSOL™ D40 Naphtha dearomatized fluid.

[0102] Embodiment 33. The method of any one of Embodiments 18 to 32, further comprising inverting the emulsion in water or a brine to form an inverted polymer solution. [0103] Embodiment 34. The method of Embodiment 33, further comprising diluting the inverted polymer solution to achieve a target concentration of the copolymer formed of acrylamide and the comonomer.

[0104] Embodiment 35. The method of Embodiment 34, wherein the target concentration is about 2,000 ppm.

[0105] Embodiment 36. The method of any one of Embodiments 33 to 35, wherein the inverted polymer solution has a filter ratio of less than or equal to 1.2, wherein the filter ratio is determined by filtering the inverted polymer solution through a 1.2 pm pore filter with a diameter of 47 mm at 15 psi of N2gas, and ambient temperature (25 °C).

[0106] Embodiment 37. The method of any one of Embodiments 33 to 35, wherein the inverted polymer solution has a filter ratio of less than or equal to 1.1, wherein the filter ratio is determined by filtering the inverted polymer solution through a 1.2 pm pore filter with a diameter of 47 mm at 15 psi of N2gas, and ambient temperature (25 °C).

[0107] Embodiment 38. A stabilizer comprising poly(stearylmethacrylate-co-methacrylic acid); and a fluid comprising EXXSOL™ D40 Naphtha dearomatized fluid, EXXSOL™ DI 00 low aromatic hydrocarbon solvent, or a combination thereof.

[0108] Embodiment 39. The stabilizer of Embodiment 38, wherein a mole ratio of stearylmethacrylate monomer to methacrylic acid monomer in the poly(stearylmethacrylate- co-methacrylic acid) is about 1-3: 1.

[0109] Embodiment 40. The stabilizer of Embodiment 38, wherein a mole ratio of stearylmethacrylate monomer to methacrylic acid monomer in the poly(stearylmethacrylate- co-methacrylic acid) is about 2: 1.

[0110] Embodiment 41. The stabilizer of any one of Embodiments 38 to 40, further comprising sorbitan monooleate and/or another compound figured to reduce or eliminate gelling over time.

[0111] Embodiment 42. The stabilizer of Embodiment 41, wherein the sorbitan monooleate is present at an amount of about 1 % to about 3 %, by weight, based on the weight of the stabilizer.

[0112] Embodiment 43. The stabilizer of any one of Embodiments 38 to 42, wherein the poly(stearylmethacry late-co-methacrylic acid) is present in the stabilizer at an amount of about 10 % to about 25 %, by weight, based on the weight of the stabilizer.

[0113] Embodiment 44. The stabilizer of any one of Embodiments 38 to 42, wherein the poly(stearylmethaciylate-co-methacrylic acid) is present in the stabilizer at an amount of about 15 % to about 20 %, by weight, based on the weight of the stabilizer.

[0114] Embodiment 45. A water-in-oil emulsion comprising the stabilizer of any one of Embodiments 38 to 44; a copolymer formed of acrylamide and a comonomer; water; an inverting surfactant; and an organic liquid.

[0115] Embodiment 46. The water-in-oil emulsion of Embodiment 45, wherein the stabilizer is present at an amount of about 1 % to about 10 %, about 1 % to about 9.8 %, about 1 % to about 8 %, by weight, based on the weight of the water-in-oil emulsion.

[0116] Embodiment 47. The water-in-oil emulsion of Embodiment 45 or 46, wherein the organic liquid comprises EXXSOL™ D100 low aromatic hydrocarbon solvent, EXXSOL™ D40 Naphtha dearomatized fluid, or a combination thereof. [0117] Embodiment 48. The water-in-oil emulsion of Embodiment 47, wherein a weight ratio EXXSOL™ DI 00 low aromatic hydrocarbon solvent to EXXSOL™ D40 Naphtha dearomatized fluid in the water-in-oil emulsion is about 150-175:15-30.

[0118] Embodiment 49. The water-in-oil emulsion of any one of Embodiments 45 to 48, wherein an inverted polymer solution of the water-in-oil emulsion having a 2,000 ppm concentration of the copolymer formed of acrylamide and a comonomer (e.g., poly(acrylamide-co-sodium acrylate)) has a filter ratio of less than or equal to 1 .2, wherein the filter ratio is determined by filtering the inverted polymer solution through a 1.2 pm pore filter with a diameter of 47 mm at 15 psi of N2 gas, and ambient temperature (25 °C).

[0119] Embodiment 50. The water-in-oil emulsion of any one of Embodiments 45 to 48, wherein an inverted polymer solution of the water-in-oil emulsion having a 2,000 ppm concentration of a copolymer formed of acrylamide and a comonomer has a filter ratio of less than or equal to 1.1, wherein the filter ratio is determined by filtering the inverted polymer solution through a 1.2 pm pore filter with a diameter of 47 mm at 15 psi of N2 gas, and ambient temperature (25 °C).

[0120] Embodiment 51. The water-in-oil emulsion of any one of Embodiments 45 to 48, wherein an inverted polymer solution of the water-in-oil emulsion having a 2,000 ppm concentration of the copolymer formed of acrylamide and a comonomer has a filter ratio of less than or equal to 1.05, wherein the filter ratio is determined by filtering the inverted polymer solution through a 1.2 pm pore filter with a diameter of 47 mm at 15 psi of N2 gas, and ambient temperature (25 °C).

[0121] Embodiment 52. A method of inverting an emulsion, the method comprising: providing the water-in-oil emulsion of any one of Embodiments 45 to 51; and inverting the water-in-oil emulsion in an aqueous liquid, such as a brine, to form an inverted polymer solution.

[0122] Embodiment 53. A method of treating a subterranean formation, comprising contacting the subterranean formation with the inverted polymer solution of any one of Embodiments 33 to 37.

[0123] Embodiment 54. The method of Embodiment 53, wherein the subterranean formation is a hydrocarbon-containing formation.

[0124] Embodiment 55. The method of any one of Embodiments 53 or 54, wherein contacting the subterranean formation with the inverted polymer solution is part of a hydrocarbon recovery process, for example, enhanced oil recovery (EOR). [0125] Embodiment 56. The method, stabilizer, or emulsion of any of the preceding embodiments, wherein an inverted water-in-oil emulsion comprising the stabilizer, as described herein under the heading “Inverting Water-m-Oil Emulsions,: has (i) a brine viscosity of at least 26, 27, 28, 29, or 30, (ii) a filter ratio of 1.3 or less, 1.2 or less, 1.1 or less, or 1 or less, or (iii) a combination thereof.

[0126] Embodiment 57. The method, stabilizer, or emulsion of any of the preceding embodiments, wherein inverted water-in-oil emulsions comprising the stabilizer, as described herein under the heading “Inverting Water-in-Oil Emulsions, have an average brine viscosity that is at least 10 %, at least 15 %, at least 20 %, at least 25 %, or least 30 % greater than comparable water-in-oil emulsions that include a stabilizer (i) formed with an initiator other than dimethyl 2,2’ -azobis(2-methylpropi onate) and/or (ii) do not include D40 or EXXSOL™ DI 00 low aromatic hydrocarbon.

EXAMPLES

[0127] The present invention is further illustrated by the following examples, which are not to be construed in any way as imposing limitations upon the scope thereof.

[0128] On the contrary, it is to be clearly understood that resort may be had to various other aspects, embodiments, modifications, and equivalents thereof which, after reading the description herein, may suggest themselves to one of ordinary skill in the art without departing from the spirit of the present invention or the scope of the appended claims.

[0129] Thus, other aspects of this invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein.

Example 1 - Stabilizers, Emulsions, and Inverted Polymer Solutions

[0130] The reactor components listed at Table 1 were weighed into a four-port, jacketed reaction vessel that was fitted with a reflux condenser connected to a nitrogen bubbler, a nitrogen subsurface inlet, a thermocouple for recording temperature, and an overhead stirrer. [0131] The solution in the sealed reactor was purged with nitrogen for one hour.

[0132] The monomer feed solution was then prepared in the monomer vessel according to Table 1.

[0133] The reaction vessel contents were heated to the indicated polymerization temperature. The monomer solution was then fed into the reaction vessel over three hours using a peristaltic pump. [0134] The post-polymerization dilution solvent and sorbitan monooleate (SMO) were added to the cooled polymer solution.

Table 1. Procedural Information

¹ Refer to Table 2. ² Azobisisobutyronitrile.

³ V-601 oil soluble initiator (FUJIFILM® Wako Pure Chemical Corporation, USA) (dimethyl

2,2'-azobis(2-methylpropionate)) (“V-601”).

⁴ LUPEROX® 531M60 polymer initiator (Arkema, USA). ⁵ V-59 oil soluble initiator (FUJIFILM® Wako Pure Chemical Corporation, USA) (2,2’- azobis(2-methylbutyronitrile) (“V-59”).

Poly (aery lamide-co-monomer) Synthesis Procedures

[0135] EPAMs were prepared by standard methods as described in WO 2014146064A2, which involved preparing an aqueous phase that contained monomers, including acrylamide, a chelating agent, a chain transfer agent and water in a ratio of 40.0 wt% : 0. 10 wt% : 0.23% : 59.7, respectively. The monomers used in synthesizing the inverse emulsion examples 21 - 39 in Table 2 were acrylamide and sodium acrylate in a 7:3 mole ratio. The monomers used in synthesizing the inverse emulsion example 40 in Table 2 were acrylamide and sodium 2- acrylamido-2-methylpropane sulfonate in a 75:25 mole ratio. These solutions were then adjusted to a neutral pH. An oil phase was prepared by combining an emulsifier, the stabilizer of this invention, and oils in a ratio of 6 wt% : 22 wt% : 72 wt%. The aqueous and oil phases were combined with high shear mixing to provide the monomer emulsion. The monomer emulsion was purged with nitrogen in a sealed reactor, followed by slow addition of a polymerization initiator. The resulting exotherm was maintained below 50 °C by rate of initiator addition and as necessary, cold water in contact with the reactor. Polymerization was considered complete when there was no further exotherm. The polymer emulsion was cooled to ambient temperature and then sufficient inverting surfactant (i.e., a surfactant having an HLB value of about 10 to about 20) was added that gave a homogeneous brine solution of 0.2% acrylamide polymer.

[0136] Alternatively, the polymer emulsion could be concentrated by distilling away water and oil, followed by addition of sufficient inverting surfactant that gave a homogeneous brine solution of 0.2% acrylamide polymer, to form the final concentrated emulsion.

Inverting Water-in-Oil Emulsions

[0137] A brine solution of 0.50 wt% Na, 0.06 wt% Ca, 0.02 wt% Mg, and 0.95 wt% Cl was used. The polymer emulsions were inverted and diluted into the brine to target concentrations of 2000 ppm in the brine by mixing at 500 rpm using an overhead mixer for 2 hours.

[0138] The filter ratio (FR) of the inverted polymer solutions was determined using the standard procedure described, for example, in Koh, H. Experimental Investigation of the Effect of Polymers on Residual Oil Saturation. Ph.D. Dissertation, University of Texas at Austin, 2015; Levitt, D. The Optimal Use of Enhanced Oil Recovery Polymers Under Hostile Conditions. Ph D. Dissertation, University of Texas at Austin, 2009; and Magbagbeola, O. A. Quantification of the Viscoelastic Behavior of High Molecular Weight Polymers used for Chemical Enhanced Oil Recovery. M. S. Thesis, University of Texas at Austin, 2008, each of which is hereby incorporated by reference.

[0139] Briefly, a 220 g solution of inverted solution in the brine, having a copolymer concentration of 2000 ppm, was filtered through a 1.2 pm ISOPORE™ polycarbonate filter with a diameter of 47 mm at 15 psi (plus or minus 10% of 15 psi) pressure and ambient temperature (25° C.) As expressed in the formula below, the FR was calculated as the ratio of the time for 180 to 200 g of the polymer solution to filter divided by the time for 60 to 80 g of the polymer solution to filter.

[0140] For the composition to qualify for further testing, the composition was required to exhibit a FR of less than or equal to 1.2. As the 1.2 FR was a strict laboratory requirement for polymer qualification, clean, laboratory-grade filtered water was used when necessary. Table 2. Brine Viscosities and Filter Ratios (FR) of Brine-Polymer Solutions

¹ X indicates plugged filters

[0141] The passing criteria for filter ratio is <1.2. The stabilizer solvent and initiator combinations of Isopar G with either AIBN or V-59 provided polymer emulsions whose resulting brine-polymer solutions had passing filter ratios (Table 2; Inverse emulsion examples 21-24).

[0142] Table 2 also demonstrates that D40 solvents have a higher viscosity than other tested stabilizers. The average brine viscosities obtained from using D40-V601 stabilizers (Table 2; stabilizer examples 15-18 and 20) was 27.7, while the viscosity of those samples not using D40-V601 (Table 2; stabilizer 1-14 and 19) was 20.9. Performing a t-test on these two averages results in a t-value of 0.017, enabling rejection of the null hypothesis that there is no difference between the populations. In other words, with at least 95% confidence, the D40-V601 group of samples is statistically different from the remaining samples.

[0143] Substituting either DI 00 or D40 solvents for Isopar G in the stabilizer synthesis coupled with one of the initiators, AIBN, 531, or V-59 provided polymer emulsions whose resulting brine-polymer solutions either plugged the filter or gave the brine-polymer solutions filter ratios >1.2 (Table 2; Inverse emulsion examples 25-34).

[0144] In this example, it was surprisingly discovered that only when the D40 solvent was coupled with the V-601 initiator in the stabilizer synthesis were the resulting brine-polymer solutions able to achieve filter ratios <1.2 (Table 2; Inverse emulsion examples 35-38 and 40).

[0145] Concentrating the poly(acrylamide-co-sodium acrylate) emulsions by distilling away the water and oil did not affect the filter ratios of the resulting brine-polymer solutions (Table 2; FR after concentration).

Claims

Claims:

1. A method of producing a stabilizer, the method comprising: contacting one or more monomers and an initiator in a fluid for a time and at a temperature effective to form in the fluid a polymer of the one or more monomers; wherein the initiator comprises dimethyl 2,2’ -azobis(2-methylpropi onate); and wherein the fluid comprises EXXSOL™ D40 Naphtha dearomatized fluid, EXXSOL™ D100 low aromatic hydrocarbon solvent, or a combination thereof.

2. The method of claim 1, wherein the one or more monomers comprise steary Imethacrylate and methacrylic acid.

3. The method of claim 2, wherein the contacting of the one or more monomers and the initiator comprises: providing a first mixture comprising a first portion of the one or more monomers, a first portion of the initiator, and a first portion of the fluid; providing a second mixture comprising a second portion of the one or more monomers, a second portion of the initiator, and a second portion of the fluid; and contacting the first mixture and the second mixture; wherein the first portion of the one or more monomers consists of steary Imethacrylate, and the second portion of the one or more monomers comprises steary Imethacrylate and methacrylic acid; wherein a weight ratio of the EXXSOL™ D40 Naphtha dearomatized fluid to the dimethyl 2,2 ’-azobis(2-methylpropi onate) to the steary Imethacrylate in the first mixture is about 250-300:0.1-0.6: 15-45; and wherein a weight ratio of the EXXSOL™ D40 Naphtha dearomatized fluid to the stearylmethacrylate to the methacrylic acid to the dimethyl 2,2’-azobis(2- methylpropionate) in the second mixture is about 350-400: 100-150:10-30:0.5-2.5.

4. The method of claim 1, wherein the temperature is about 80 °C to about 120 °C.

5. The method of claim 1, further comprising combining the fluid comprising the polymer with a dilution fluid and optionally sorbitan monooleate to form the stabilizer. The method of claim 5, wherein the dilution fluid comprises EXXSOL™ D40 Naphtha dearomatized fluid, EXXSOL™ DI 00 low aromatic hydrocarbon solvent, or a combination thereof. The method of claim 5, wherein the polymer is present in the stabilizer at an amount of about 10 % to about 25 %, by weight, based on the weight of the stabilizer. The method of claim 5, wherein a mole ratio of stearylmethacrylate to methacrylic acid in the polymer is about 1-3:1. A method of forming an emulsion, the method comprising: providing an aqueous phase comprising acrylamide, a comonomer, a chain transfer agent, a chelating agent, and water; providing an oil phase comprising a first organic liquid and the stabilizer formed according to the method of any one of claims 5 to 8; combining the aqueous phase and the oil phase to form the emulsion; and initiating polymerization of the acrylamide and the comonomer with a polymerization initiator to form a copolymer in the emulsion. The method of claim 9, further comprising, after the polymerization is substantially complete:

(a) contacting the emulsion with an amount of inverting surfactant; or

(b) (i) optionally contacting the emulsion with a second organic liquid, (ii) reducing a volume of the emulsion, and (iii) contacting the emulsion with an amount of inverting surfactant. The method of claim 10, further comprising: inverting the emulsion in water or a brine to form an inverted polymer solution; and optionally diluting the inverted polymer solution to achieve a target concentration of the copolymer. The method of claim 11, wherein the inverted polymer solution having a 2,000 ppm concentration of the copolymer has a filter ratio of less than or equal to 1.2, wherein the filter ratio is determined by filtering the inverted polymer solution through a 1.2 pm pore filter with a diameter of 47 mm at 15 psi of N2 gas, and ambient temperature (25 °C). A stabilizer comprising: poly(stearylmethacrylate-co-methacrylic acid); and a fluid compnsmg EXXSOL™ D40 Naphtha dearomatized fluid, EXXSOL™ D100 low aromatic hydrocarbon solvent, or a combination thereof. A water-in-oil emulsion comprising: the stabilizer of claim 13; a copolymer formed of acrylamide and a comonomer; water; an inverting surfactant; and an organic liquid; wherein the stabilizer is present at an amount of about 1 % to about 10 %, by weight, based on the weight of the water-in-oil emulsion. The water-in-oil emulsion of claim 14, wherein an inverted polymer solution of the water-in-oil emulsion having a 2,000 ppm concentration of the copolymer has a filter ratio of less than or equal to 1.2, wherein the filter ratio is determined by filtering the inverted polymer solution through a 1.2 pm pore filter with a diameter of 47 mm at 15 psi of N2 gas, and ambient temperature (25 °C).