Water-soluble hydrophobically associating polymers for improved oil recovery: A literature review

Journal of Petroleum Science and Engineering 19 Ž1998. 265–280

Water-soluble hydrophobically associating polymers for improved oil recovery: A literature review Kevin C. Taylor a

a,1

, Hisham A. Nasr-El-Din

b,)

Petroleum RecoÕery Institute, a100, 3512-33rd St. NW, Calgary, Alta., Canada T2L 2A6 b Lab R & D Center, P.O. Box 62, Saudi Aramco, Dhahran 31311, Saudi Arabia Received 21 May 1996; revised 21 August 1997; accepted 21 August 1997

Abstract Water-soluble hydrophobically associating polymers are reviewed with particular emphasis on their application in improved oil recovery ŽIOR.. These polymers are very similar to conventional water-soluble polymers used in IOR, except that they have a small number of hydrophobic groups incorporated into the polymer backbone. At levels of incorporation of less than 1 mol%, these hydrophobic groups can significantly change polymer performance. These polymers have potential for use in mobility control, drilling fluids and profile modification. This review includes synthesis, characterization, stability, rheology and flow in porous media of associating polymers. Patents relating to the use of associating polymers in IOR are also examined. q 1998 Elsevier Science B.V. Keywords: enhanced-recovery; polymers; flooding; petroleum; synthesis; rheology

1. Introduction Water-soluble polymers are used in many oilfield operations including drilling, polymer-augmented water flooding, chemical flooding and profile modification ŽChatterji and Borchardt, 1981; Sutherland and Kierulf, 1987; Sorbie, 1991.. The role of the polymer in most IOR field applications is to increase the viscosity of the aqueous phase. This increase in viscosity can improve sweep efficiency during enhanced oil recovery processes. In drilling fluids, the solution rheology is very important. Shear thinning

)

Corresponding author. Fax: q966-3-8762811. Present address: Lab R&D Center, P.O. Box 62, Saudi Aramco, Dhahran 31311, Saudi Arabia. 1

fluids are desired that can suspend drilling cuttings at low shear rates, but offer little resistance to flow at high shear rates. The use of water-soluble polymers for improved oil recovery ŽIOR. has been extensively reviewed ŽMacWilliams et al., 1973; Needham and Doe, 1987; Littman, 1988; Yen et al., 1989; Sorbie, 1991.. Commercially, both partially hydrolyzed polyacrylamide ŽHPAM. and biopolymers Žsuch as xanthan gum. are used in the oil industry. These traditional polymers rely on chain extension and physical entanglement of solvated chains for viscosity enhancement. The carboxylate groups in HPAM cause chain expansion due to repulsion of the ionic groups, which leads to higher solution viscosity. The viscosity of a solution of HPAM increases as its molecular weight increases, providing that other factors remain

0920-4105r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 9 2 0 - 4 1 0 5 Ž 9 7 . 0 0 0 4 8 - X

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K.C. Taylor, H.A. Nasr-El-Dinr Journal of Petroleum Science and Engineering 19 (1998) 265–280

constant. As a result, oilfield operations use high molecular weight HPAM which results in increased solution viscosity at a given polymer concentration. However, high molecular weight HPAM is irreversibly degraded by high shear rates, such as those encountered in pumps and near the well bore area. High shear rates cause breakage of the polymer backbone, resulting in an irreversible decrease in viscosity. The higher the molecular weight of HPAM, the more easily it is shear degraded ŽSorbie, 1991.. High molecular weights, however, are required to produce high viscosities at low concentrations. In addition, the viscosity of HPAM decreases rapidly as salinity or hardness increases ŽNasr-El-Din et al., 1991.. This is due to shielding of ionic groups, which reduces repulsion and causes chain contraction. The complexing ability of the carboxylate groups of HPAM can lead to polymer precipitation in the presence of high concentrations of divalent ions ŽZaitoun and Potie, 1983.. In contrast to polyacrylamide, xanthan gum is a rigid polysaccharide that is not readily shear degraded and is not sensitive to an increase in salinity or divalent ion concentration ŽNasr-El-Din and Noy, 1992.. Disadvantages of xanthan are higher cost, high susceptibility to biodegradation and potential for injectivity problems due to cellular debris remaining from the manufacturing process. Xanthan is used extensively in drilling fluids because it is not subject to shear degradation. In general, polyacrylamide is efficient at increasing viscosity up to about 1 mass% sodium chloride, while xanthan gum is more efficient at higher salt concentrations. Solutions of both polymers exhibit decreasing viscosity as temperature is increased. Many oil reservoirs contain connate water with high concentrations of sodium chloride and divalent ions, requiring the use of expensive and easily biodegraded xanthan biopolymer. Water-soluble hydrophobically associating polymers are water-soluble polymers that contain a small number of hydrophobic groups attached directly to the polymer backbone. In aqueous solutions, the hydrophobic groups of these polymers can associate to minimize their exposure to the solvent, similar to the formation of micelles by a surfactant above its critical micelle concentration. This association results in an increase in the hydrodynamic size of the polymer that in-

creases solution viscosity. The potential exists to use associating polymers as mobility control agents in reservoir brine of high salinity and high divalent ion concentration ŽMcCormick et al., 1993; Uhl et al., 1993.. In addition, their unique flow properties may be advantageous in drilling fluids and in conformance control applications. Schulz et al. Ž1994. reviewed synthetic routes designed to overcome the problems of mixing and reacting oil-soluble and water-soluble monomers and reagents. They also discussed some direct copolymerization and post-polymerization methods, as well as hydrophobe determination with NMR, UV and degradationrGC. The development and properties of associating polymers was also briefly reviewed by Hawe Ž1993.. Another significant type of associating polymer is prepared by hydrophobically modifying hydroxyethyl cellulose ŽHEC. or hydroxypropyl cellulose ŽHPC. by reaction with alkyl halides, acid halides, acid anhydrides, isocyanates, or epoxides ŽLandoll, 1982; McCormick et al., 1989.. These polymers are claimed to have potential in IOR ŽLandoll, 1985; Sau and Landoll, 1989.. Evani Ž1984. and van Phung and Evani Ž1986. claim that cellulosic associating thickeners have acceptable salt tolerance, but are ineffective at low concentrations and have poor thermal stability. They are also readily biodegraded. The synthesis, solution properties and rheology of associating cellulosic thickeners have been studied ŽGoodwin et al., 1989; Sau and Landoll, 1989; Dersch, 1994. and are not examined in further detail in this work. The limitations of this class of associating polymer are a serious drawback for use in IOR. This review examines the use of associating polyacrylamides for improved oil recovery, and includes synthesis, characterization, stability, rheology, and flow in porous media.

2. Discussion 2.1. Background The idea of using water-soluble associating polymers in improved oil recovery is one that followed several phases of polymer development in the coat-

K.C. Taylor, H.A. Nasr-El-Dinr Journal of Petroleum Science and Engineering 19 (1998) 265–280

ings industry. However, the first associating polymers were prepared as models to mimic conformation behaviour of proteins ŽStrauss and Jackson, 1951; Dubin and Strauss, 1967, 1970.. Some of the first hydrophobically-modified water-soluble polymers were prepared by partial esterification of maleic anhydriderstyrene copolymers with nonionic ethoxylated alcohol surfactants ŽEvani and Rose, 1987; Beihoffer et al., 1989.. These polymers were developed as part of a program to address deficiencies in coatings rheology ŽEvani and Rose, 1987.. However, susceptibility to thermal degradation and alkaline hydrolysis limited their use. This problem is common to long chain polyethers, which decompose in the presence of oxygen, especially at high pH values ŽEmmons and Stevens, 1983.. This le d to th e d e v e lo p m e n t o f m a le ic anhydriderstyrenervinyl benzyl polyglycol ether copolymers ŽEvani and Corson, 1976, 1978.. Hydrophobically modified ethoxylated urethane ŽHEUR. polymers were introduced in the 1960s and eventually found significant use in water-based latex coatings ŽGlass and Karunasena, 1989.. Thus, the largest market initially was in water-based coatings. Acrylamide-based hydrophobically associating polymers were extensively developed in the 1980s. Applications for enhanced oil recovery were pursued because of the large market potential that existed. Several patents have been issued for the use of associating polymers in IOR ŽSchwab et al., 1978; Landoll, 1984; Bock et al., 1987b,d, 1992; Evani, 1989.. 2.2. Synthesis of associating polymers Associating polymers have been prepared by two general methods. The first method is the copolymerization of water-soluble and hydrophobic monomers. The second method is the modification of polymers after polymerization to introduce hydrophobic or hydrophilic groups. Copolymerization by micellar polymerization is the most common method of associating polymer synthesis and is discussed in detail. Hydrophobically associating block copolymers have been prepared by anionic polymerization ŽSchwab et al., 1978; Bock et al., 1988a; Valint and B ock, 1988 . . C opolym ers w ith t-butyl

267

styrenerstyrenert-butyl styrene blocks were prepared. Bock et al. Ž1988a. also prepared t-butyl styrenerstyrene block copolymers. These copolymers were selectively sulfonated to provide watersolubility. Thus in block copolymers, the hydrophobic group is a segment of the polymer backbone, in this case the segment containing t-butyl phenyl groups. Block copolymers based on styrene are not considered as possible candidates for IOR because they are not soluble in sodium chloride solutions. Associating polymers are commonly prepared using acrylamide and free radical polymerization. Acrylamide is the monomer most suited for the manufacture of high molecular weight water-soluble polymers ŽBeihoffer et al., 1989.. Although other monomers have been used to prepare associating polymers, acrylamide has been the most successful at producing water-soluble associating copolymers that are effective at polymer concentrations below 1 mass%. Schulz Ž1991. has reviewed fundamental and practical aspects of free radical polymerization of water-soluble monomers. Schulz et al. Ž1994. have also briefly reviewed synthetic methods for several classes of associating polymers. Associating acrylamide polymers have most commonly been prepared by copolymerizing acrylamide with a hydrophobic monomer and other monomers such as acrylic acid. Fig. 1 shows a hydrophobically associating acrylamideracrylic acidrdodecyl methacrylate copolymer. The hydrophobic monomer used to prepare the copolymer was dodecyl methacrylate. Carboxylic acid groups have been incorporated into associating polyacrylamides by base hydrolysis after polymerization ŽBock et al., 1987b,c, 1989; Siano and Bock, 1987; Jacques and Bock, 1988., but copolymerization is more common. Compositional heterogeneity has a very significant effect on rheological properties of associating polymers, and is discussed later in this section.

Fig. 1. Hydrophobically associating polyacrylamide. x: 30–100, y: 0–70, z: 0.01–1.

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Table 1 Monomers and hydrophobic monomers for free radical polymerization Vinyl sulfonate 4-Vinyl benzene sulfonate 2-Acrylamido-2-methyl-1-propanesulfonic acid ŽAMPS. N-vinyl pyrrolidinone n-Alkyl acrylates and methacrylates

Polyethoxy n-alkyl acrylates and methacrylates Acrylamides

Styrene Anionic monomers Cationic monomers Betaines Fluorocarbon-containing Silicone-containing

Bock et al., 1987d; Bock and Valint, 1988; Valint and Bock, 1992 Bock et al., 1987d; Bock and Valint, 1988; Valint and Bock, 1992 Evani, 1982, 1989; Bock et al., 1987d; Bock and Valint, 1988; Zhang et al., 1990; Middleton et al., 1991; Valint and Bock, 1992 Bock et al., 1987b, 1988b; Schulz et al., 1987a Evani, 1982, 1989; Landoll, 1985; Stanley, 1985; King and Constien, 1986; Bock et al., 1987a; Yang and Pacansky, 1990; Zhang et al., 1990, 1991, 1992; Flynn and Goodwin, 1991 Emmons and Stevens, 1983; Schulz et al., 1984, 1987c, 1988a; Evani and van Phung, 1985; Maurer et al., 1986 Emmons and Stevens, 1983; Turner et al., 1985a,b,c; Bock et al., 1987a,b,d, 1988b; Schulz et al., 1987a,b, 1988b; Siano and Bock, 1987; Bock and Valint, 1988; McCormick and Johnson, 1988, 1989; McCormick et al., 1988; van Phung and Evani, 1988; Valint et al., 1989; Yang and Pacansky, 1990; Hill et al., 1991; Middleton et al., 1991; Winnik et al., 1991a,b; Biggs et al., 1992; Valint and Bock, 1992 Evani and Corson, 1976; Evani, 1982, 1989; Shay and Kravitz, 1987, 1988 van Phung and Evani, 1986; Ching, 1987; Peiffer, 1990 Bock et al., 1987a; Schulz et al., 1987b, 1988b; Peiffer, 1989, 1990, 1991; Yang and Pacansky, 1990 McCormick and Hester, 1990 Zhang et al., 1990, 1991, 1992 Zhang et al., 1991

Many different monomers and hydrophobic monomers have been used to prepare acrylamidebased associating polymers by free radical polymerization. These are summarized, with references, in Table 1. In all cases, acrylamide is the major monomer. In many cases, acrylamide and acrylic acid are copolymerized with a hydrophobic monomer to produce associating analogues of HPAM. Sulfonate-containing monomers including vinyl sulfonate, 4-vinyl benzene sulfonate and 2-acrylamido2-methyl-1-propanesulfonic acid ŽAMPS. have been used to replace acrylic acid and improve salt sensitivity. N-vinyl pyrrolidinone ŽNVP. has been used in large proportions to make the resulting polymer more resistant to base-catalyzed hydrolysis of the acrylamide. With acrylates or methacrylates, n-alkyl esters and polyethoxy n-alkyl esters have been reported as hydrophobic monomers. Other hydrophobic monomers have been prepared based on acrylamides and styrene. Hydrophobic monomers that are anionic, cationic or betaines have been reported. Hydrophobic monomers containing fluorocarbons or silicone have also been prepared.

Associating polymers have been prepared by incorporating hydrophobic groups into the polymer after the polymerization process. The advantage of this approach is that commercially available polymers can be used as starting material. A disadvantage is that reactions involving viscous polymer solutions are not easily carried out because of problems associated with mixing and reaction homogeneity. Hydrophobically modified polyŽacrylic acid. has been prepared from polyacrylic acid ŽIliopoulos et al., 1991; Wang et al., 1988, 1991.. The reaction must be carried out in an aprotic solvent such as N-methyl pyrrolidinone. Molecular weights of the polyŽacrylic acid. starting material up to 500,000 grmol were employed. Kevlar has been modified by adding hydrophobic groups and sulfonate functionality to make it hydrophobically associating in up to 10 mass% NaCl solution ŽPeiffer and Kaladas, 1990.. The product is thermally stable, but the synthesis is relatively expensive. Polyacrylamide has been subjected to transamidation by heating it in an aqueous solution under

K.C. Taylor, H.A. Nasr-El-Dinr Journal of Petroleum Science and Engineering 19 (1998) 265–280

pressure at 1508C with water-soluble amines ŽFong, 1991.. Due to the high temperatures used, the polyacrylamide was hydrolyzed and the range of hydrolysis of the product was up to 40%. Maximum molecular weight is low, approximately 16,000 grmol. Associating polymers have been prepared by modification of styrenermaleic anhydride copolymers ŽPeiffer et al., 1992.. The copolymer is first fully sulfonated to provide water solubility and is then reacted with an alkyl amine to incorporate hydrophobic groups. The preparation of acrylamide-based hydrophobically associating polymers presents problems because both water-soluble and water-insoluble monomers must be copolymerized. The hydrophobic monomers do not normally dissolve in water, which is the best solvent for polymerization of acrylamide. Mechanical stirring will disperse the hydrophobic monomer into small droplets, but polymerization results in a latex or a polymer that does not incorporate hydrophobic groups ŽValint and Bock, 1992.. Mixed solvents such as waterralcohol can dissolve both the hydrophobic and the hydrophillic monomers, but are not good solvents for the resulting polymer. Consequently, polymer precipitates from solution as the polymerization proceeds. The resulting polymer is generally of low molecular weight, due in part to insolubility of high molecular weight material in the solvent and to chain transfer processes in the organic solvent. Most of the preparations of associating polymers have used a micellar polymerization technique, in which a surfactant such as sodium dodecyl sulfate ŽSDS. is used in an aqueous solution to solubilize the hydrophobic monomer. Micelles of SDS may then contain molecules of the hydrophobic monomer. Although other surfactants can be used, SDS is readily available in a pure form. Impurities such as alcohols or heavy metal cations could interfere with the polymerization, resulting in polymers of reduced molecular weight. Hill et al. Ž1993. have compared the effect of several polymerization techniques on rheological properties of the resulting associating polymers. A technique for the preparation of associating polymers that has seen little use is polymerization in a microemulsion, containing water, monomers, surfactant and oil ŽTurner et al., 1985c.. This technique

269

was superseded by the introduction of micellar polymerization. Associating polymers have also been prepared using hydrophobic monomers that are surfactants. These hydrophobic monomers ŽSchulz et al., 1984, 1987c, 1988a; Maurer et al., 1986; van Phung and Evani, 1986; Ching, 1987; Shay and Kravitz, 1987, 1988; Peiffer, 1989, 1990. have been called ‘surfomers’ ŽSchulz et al., 1987c.. The efficiency of incorporation of the hydrophobic monomer into the polymer has been the subject of much research ŽMcCormick et al., 1988; Valint et al., 1989; McCormick and Hester, 1990; Flynn and Goodwin, 1991.. Biggs et al. Ž1992. examined in detail the effect of surfactant concentration on hydrophobic monomer incorporation into an acrylamide copolymer. They found that the reaction rate for acrylamide polymerization in aqueous solution was very similar to its reaction rate in a micellar solution. Solubilization of hydrophobic monomers within the micelles causes a positive increase in their rate of incorporation into the copolymer. Total incorporation of hydrophobic monomer at high conversion was greater than 90%. The higher the number of hydrophobic monomers per micelle, the greater the increase in the rate of incorporation. This means that at values of hydrophobic monomer to micelle of much greater than unity, the hydrophobic monomer can be depleted before the end of the polymerization. This results in homopolymer being produced at the end of the polymerization, and a highly polydisperse product. However, if the hydrophobic monomer to micelle ratio is approximately one, the reactivity is only slightly higher than that of acrylamide. Biggs et al. also concluded that the rate of monomer exchange between micelles is significant and fast relative to monomer reaction with a growing radical. The result was a polymer with blocks of hydrophobic groups. Valint and Bock Ž1992. found that the viscosity of the resulting polymer Žafter purification by precipitation. showed a maximum as a function of polymerization surfactant concentration. The surfactant concentration for maximum viscosity increased when the hydrophobe level of the polymer was increased. Valint et al. Ž1987, 1989. used UV-absorbing hydrophobic monomers Ž4-alkyl phenyl acrylamides. and found that hydrophobe incorporation at high conversion was 87–97%. At low conversions, incor-

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Table 2 Free radical polymerization conditions Initiator

Temp. Ž8C.

Monomers Žmass%.

wh x Ždlrg a .

Ref.

K 2 S2 O8 K 2 S2 O8 K 2 S2 O8

50 50 50

3.0 3.0 2–4

— 3.3–6.6 1.6–8.0

K 2 S2 O8 K 2 S2 O8 K 2 S2 O8 K 2 S2 O8 K 2 S 2 O 8 rNa 2 S 2 O5 K 2 S 2 O 8 rNa 2 S 2 O5 K 2 S 2 O 8 rTEA AIBN AIBN AIBN AIBN AIBN Vazo 33 Vazo 33

55 50 60 50 25 25 20 45 60 60 60 60 20–30 25

3.0 3.0 5 3.0 4.5 4–12 10.0 3.0 20 10 10 20 3.0 5

2.6–8.3 3.3–6.6 — 5–7 10–13 — 28–75 b 8–12 — 12–14 b — 8–10 b 6–11 —

Landoll, 1982; Goodwin et al., 1989; Fong, 1991 Sau and Landoll, 1989 Valint et al., 1989; McCormick et al., 1988; Biggs et al., 1992; Schulz et al., 1987b Schulz et al., 1988b McCormick and Hester, 1990 Turner et al., 1985a; McCormick and Johnson, 1989 Peiffer, 1990 Landoll, 1982; Goodwin et al., 1989; Fong, 1991 Peiffer et al., 1992 Bock et al., 1987a Wang et al., 1988, 1991; Flynn and Goodwin, 1991 McCormick et al., 1989; Evani and Rose, 1987 Emmons and Stevens, 1983 Winnik et al., 1991a Magny et al., 1991 Wang et al., 1988, 1991; Flynn and Goodwin, 1991 Constien and King, 1985

a

2 mass% NaCl unless noted. X 3 mass% NaCl, TEA: triethylamine; NVP: N-vinyl-2-pyrrolidinone; Vazo 33: 2,2 azobisŽ2,4-dimethyl-4-methoxylvaleronitrile.; AIBN: X 2,2 -azobisŽ2-methylpropionitrile.. b

poration was approximately 140% of the initial level. Schulz et al. Ž1988a. measured hydrophobic m o n o m e r in c o r p o r a tio n w ith n o n y lphenoxyŽoxyethylene.10 acrylate, a hydrophobe-containing surfactant monomer Žsurfomer.. At low conversions, they found a level of incorporation of 23% when the initial surfomer concentration Žbefore polymerization. was 1 mol%. It is expected that surfomers, which do not require added surfactant for polymerization, will produce highly heterogeneous polymers. In fact, Bhattacharyya and St. John Ž1991. claim that timed addition of a cationic monomer over the course of the polymerization resulted in more random incorporation into the final polymer, as would be expected. Sodium dodecyl sulfate is most commonly used for micellar polymerizations, at concentrations of 1 to 3 mass% ŽEvani, 1982, 1984, 1989; Constien and King, 1985; Evani and van Phung, 1985; Turner et al., 1985b; Bock et al., 1987b,d, 1988b; Schulz et al., 1987a, 1988b; Siano and Bock, 1987; Bock and Valint, 1988; Valint and Bock, 1992.. When the monomer N-vinyl pyrrolidinone is used, less surfactant is required to solubilize a hydrophobic monomer ŽBock et al., 1987b, 1988b; Schulz et al., 1987a..

Table 2 summarizes initiators, temperatures, and monomer concentrations used for the preparation of hydrophobically associating polymers. Intrinsic viscosity Žwh x. is reported where available. With the use of a redox initiator, low temperature and high monomer concentration, very high molecular weight associating polymers can be obtained ŽSiano and Bock, 1987.. In general, however, intrinsic viscosities from 2 to 10 dlrg can be prepared with either persulfate or diazo initiators in the absence of chain transfer agents. Values of MrŽ I . 0.5 are generally 30 to 100, where M is the total monomer concentration and I represents initiator concentration, both in units of molesrl. Low concentrations of isopropanol as a chain transfer agent have been used to prepare associating polymers of lower molecular weight ŽEvani, 1989; van Phung and Evani, 1988.. Several methods of polymer purification have been used after micellar polymerization. In some cases, the polymer solution is diluted and used as is ŽEvani, 1982, 1989; Evani and van Phung, 1985; van Phung and Evani, 1986, 1988; Siano and Bock, 1987; Ching, 1987; Shay and Kravitz, 1987, 1988; Fong, 1991.. More commonly, the polymer is precipitated in a nonsolvent such as methanol, filtered, and dried

K.C. Taylor, H.A. Nasr-El-Dinr Journal of Petroleum Science and Engineering 19 (1998) 265–280

under vacuum ŽSchulz et al., 1987c; Valint et al., 1987; McCormick and Johnson, 1988; Siano et al., 1989; Valint et al., 1989; Biggs et al., 1992.. Alternately, the polymer solution is dialyzed against distilled water for 1 to 3 days followed by dilution to remove low molecular weight impurities ŽMaurer et al., 1986; Schulz et al., 1987c; Flynn and Goodwin, 1991; Zhang et al., 1992. or by freeze drying ŽSchulz et al., 1984, 1987c.. The rheological properties of the resulting polymer solutions are significantly affected by the isolation process. Highest viscosities are obtained when the polymer is purified by dilution and dialysis, as opposed to methods that purify the polymer by producing a solid material ŽSchulz et al., 1987c.. This may be due to very slow hydration of a ‘dry’ polymer that results from the partially hydrophobic character of the polymer. 2.3. Characterization of hydrophobic interactions The association phenomenon has been investigated in detail by using fluorescent probes such as pyrene ŽMcCormick and Johnson, 1988, 1989; Flynn and Goodwin, 1991; Winnik et al., 1991a; Wang et al., 1991. or 8-anilino-1-napthalene sulfonic acid ŽSiano et al., 1989. and by incorporating a fluorescent hydrophobic monomer into an associating polymer ŽWinnik et al., 1991b.. More recently, Varadaraj et al. Ž1993, 1994. used a solvatochromic dye to probe hydrophobic microdomains. Pyrene is often used because it has extremely low solubility in water and a characteristic fluorescence emission spectrum. Pyrene is solubilized by hydrophobic clusters such as micelles or associating polymers, which results in an increase in fluorescence and a shift in the emission spectrum. When two or more pyrene molecules are present in a hydrophobic region, an excimer forms which has a characteristic emission spectrum. From quantitative measurements of pyrene monomer and excimer fluorescence, Flynn and Goodwin Ž1991. calculated that an average of approximately ten hydrophobes was required to form a hydrophobic region in an acrylamiderdodecyl methacrylate copolymer. They arrive at the same average number using shear wave propagation measurements and a network model. Pyrene fluorescence measurements have

271

shown that the onset of aggregation occurs at concentrations lower than the critical aggregation concentration, c ) ŽMcCormick and Johnson, 1988, 1989; Siano et al., 1989; Wang and Winnik, 1990.. At concentrations above c ) , intermolecular hydrophobic associations between polymers dominate polymer behavior in solution. At concentrations below c ) , intramolecular hydrophobic associations within the polymer dominate the behavior. McCormick and Johnson Ž1988, 1989. found that the fluorescence lifetime of pyrene began to increase at associating polymer concentrations of greater than 0.02 grdl for a polymer having c ) of 0.15 grdl. From fluorescence measurements, McCormick and Johnson Ž1988, 1989. have suggested that there are three concentration regions of importance for associating polymers. At low concentrations, no intramolecular association occurs. At intermediate concentrations, there is some association but no networking. This corresponds to an increase in pyrene solubilization, but no viscosity enhancement. At high concentrations, above c ) , extensive intermolecular association leads to network structures and a large increase in viscosity. 2.4. Hydrolytic stability of associating polymers Bock et al. Ž1987d. examined the hydrolytic stability of some associating polymers under neutral conditions. Polymer solutions at a concentration of 2000 ppm in brine Ž3 mass% NaCl q 0.3 mass% calcium chloride. were heated at 938C for 100 days. The increase in the degree of hydrolysis was much lower when AMPS was incorporated into the polymer. For instance, at 938C, 78% of the amide groups in polyacrylamide ŽPAM. were hydrolyzed after 100 days. For an associating polymer containing 40 mol% AMPS, only 36% of the amide groups were hydrolyzed during this time period. When the associating polymer contained 52 mol% NVP, only 5% of the amide groups were hydrolyzed under the same conditions ŽBock et al., 1987b.. Associating polymers containing NVP were hydrolyzed more slowly than commercial PAM at 408C ŽBock et al., 1987b.. Surprisingly, associating groups in the polymer further reduced the rate of amide group hydrolysis, as compared to an acrylamiderNVP copolymer.

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2.5. Rheology Rheological properties of associating polymers depend on several factors, including the average molecular weight, degree of hydrolysis, hydrophobe type, degree of incorporation of hydrophobe and distribution of hydrophobe ŽMcCormick et al., 1989; Bock et al., 1994.. The solubility of water-soluble associating polymers decreases as the hydrophobe content increases ŽMcCormick et al., 1989.. As molecular weight of the polymer increases, or hydrophobe chain length increases, the amount of hydrophobe required to make the polymer insoluble decreases. Obviously, this will limit the maximum hydrophobe content that can be introduced into an associating polymer. When fluorocarbon-containing hydrophobic groups are used, much lower concentrations of the hydrophobic group are required to make the resulting associating polymer insoluble ŽZhang et al., 1990, 1991, 1992.. One way to increase the solubility of associating polymers in water is to introduce ionic character on the polymer backbone ŽMcCormick et al., 1989.. Such ionic character can be obtained by hydrolyzing some of the amide groups to carboxylate groups ŽBock et al., 1989; Wang et al., 1991. or by copolymerizing acrylamide with sulfonate-containing monomers ŽBock et al., 1987d; Bock and Valint, 1988; Evani, 1989; Zhang et al., 1990; Middleton et al., 1991; Valint and Bock, 1992.. It should be mentioned that the introduction of ionic groups into the polymer backbone will modify the rheological properties of the associating polymers as will be discussed later. The introduction of hydrophobic groups into a water-soluble polymer will modify the flow behaviour of the precursor polymer. This is mainly due to intramolecular association, intermolecular association, or both ŽMcCormick et al., 1989.. The net effect of these associations depends, among other factors, on polymer concentration. If the reduced viscosity is plotted versus polymer concentration for associating and non-associating polymers, there is a critical concentration above which the associating polymer shows enhanced viscosity ŽSchulz and Bock, 1991.. This critical concentration is also known as the overlap concentration, or the critical aggregation concentration, c ) . The critical concentration of

nonassociating polymers has been discussed in detail ŽWolff, 1977; Aharoni, 1978.. The viscosity enhancement at c ) is mainly due to intermolecular association. Below c ) , the introduction of hydrophobic groups results in a slight decrease in the reduced viscosity. This reduction is due to intramolecular association, which also reduces intrinsic viscosity and leads to an increase in the Huggins constant ŽMagny et al., 1991.. More explanation of intramolecular and intermolecular association will be given in the next sections. It is important to note that the effect of the hydrophobic groups depends on polymer concentration. For this reason, it is meaningful to examine the viscosity of associating polymers in two concentration regimes: a dilute regime, where polymer concentration is less than the critical overlap concentration and a semi-dilute regime, where polymer concentration is higher than the overlap concentration. In addition, the effect of various chemical species on the flow behaviour of these polymers will be examined. 2.5.1. Viscosity of associating polymers in the dilute regime 2.5.1.1. Intrinsic Õiscosity and Huggins constant. The intrinsic viscosity, wh x, and Huggins constant, k, can be used to determine the molecular weight of the polymer and to assess the degree of hydrophobic interactions ŽBock et al., 1988a.. Therefore, it is useful to discuss these two parameters before examining the rheological properties of associating polymers. It is known that for dilute polymer solutions and according to the Flory–Huggins equation, the reduced viscosity is a linear function of polymer concentration as follows: h y h0 2 s wh x q k wh x c Ž 1. h0 c where c is the polymer concentration in grdl and h 0 is the solvent viscosity. The intrinsic viscosity and Huggins constant can be obtained by measuring the viscosity of polymer solutions having low polymer concentrations. It is important to note that these viscosity measurements should be conducted at a low shear rate to ensure that the solution viscosity is

K.C. Taylor, H.A. Nasr-El-Dinr Journal of Petroleum Science and Engineering 19 (1998) 265–280

independent of shear rate. The intrinsic viscosity and Huggins constant can be determined by fitting the experimental data using Eq. Ž1.. The intrinsic viscosity generally decreases and the Huggins constant increases as the hydrophobe content is increased at constant molecular weight ŽBock et al., 1989.. The Huggins constant is a very important measure of polymer–solvent and polymer–polymer interactions ŽBock et al., 1988a.. For random coil polymers, k is in the range 0.3 to 0.8. The intrinsic viscosity is related to the polymer weight average molecular weight, M w , through the Mark–Houwink–Sakurada equation ŽBock et al., 1988a; McCormick et al., 1989.:

wh x s K w Mw x

a

Ž 2.

where K and a are characteristics for a polymer chain under specific conditions of solvency and temperature ŽMagny et al., 1992.. 2.5.1.2. Effect of hydrophobe content. The introduction of hydrophobic groups will affect the intrinsic viscosity and the Huggins constant. Bock et al. Ž1988a. prepared copolymers of N-octylacrylamide and acrylamide using micellar copolymerization. The prepared copolymers were nonionic, had a molecular weight of 3 = 10 6 grmol and contained a hydrophobe content of 0, 0.75 and 1 mol%, respectively. Table 3 lists the intrinsic viscosity and Huggins constant for these polymers. The intrinsic viscosity decreased as the hydrophobe content was increased. This is mainly due to intramolecular association that leads to the contraction of the polymer chain. On the other hand, Table 3 shows an increase in Huggins constant with the hydrophobe content such that Huggins constant at 1 mol% hydrophobe was significantly higher than the common value of

Table 3 Intrinsic viscosity and Huggins constant, acrylamiderN-octylacrylamide copolymers Ždata from Bock et al. Ž1988a.. Hydrophobe content Žmol% n-octylacrylamide.

wh x Ždlrg.

Huggins constant, k

0 0.75 1.0

7.3 4.5 3.4

0.4 0.8 2.5

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0.3 to 0.8 for random coil polymers. Flynn and Goodwin Ž1991. also found an increasing Huggins constant as hydrophobe content was increased in acrylamiderdodecyl methacrylate polymers. Therefore, the Huggins constant can be used as a measure of the hydrophobic interactions and a value greater than 0.8 indicates association. 2.5.1.3. Effect of hydrolysis. To examine the effect of introducing ionic character to associating polymers, Bock et al. Ž1989. prepared two sets of associating polymers, each containing polymers of the same molecular weight and hydrophobe level. However, one set of polymers was hydrolyzed to a degree of hydrolysis of 18%. They found that the intrinsic viscosities of the hydrolyzed polymers were higher than that of the unhydrolyzed polymers. By introducing ionic character into the polymer, the hydrodynamic volume of the polymer chain increases because of the electrostatic repulsion between the negative charges of the carboxylate groups. The intrinsic viscosity decreased for both hydrolyzed and unhydrolyzed polymers as hydrophobe content was decreased. By increasing the hydrophobe content, the intramolecular association increases. As a result, the polymer chains coil up and the hydrodynamic volume decreases. From the work of Bock et al. Ž1989., it is important to note that ionic character and hydrophobic interactions have opposite effects on intrinsic viscosity. In the dilute regime, hydrolysis of the associating polymer increases its intrinsic viscosity, whereas increasing the hydrophobic content reduces its intrinsic viscosity. Bock et al. Ž1989. also found that the Huggins constant of the hydrolyzed polymer was lower than that of the unhydrolyzed one. The electrostatic repulsion opens the polymer chain up. This in turn improves the polymer–solvent interaction that is marked by low values of the Huggins constant.

2.5.2. Viscosity of associating polymers in the semidilute regime 2.5.2.1. Effect of polymer concentration. The effect of hydrophobic association on viscosity in the semidilute regime is different from that observed at low polymer concentrations. Bock et al. Ž1988a. exam-

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ined the variation of the reduced viscosity with polymer concentration for polyacrylamiderNoctylacrylamide copolymers having hydrophobe contents of 0.75 and 1 mol%. At a hydrophobe content of 0.75 mol%, they found that the viscosity significantly increased as polymer concentration was increased because of intermolecular association. Increasing hydrophobe content further to 1 mol% resulted in higher viscosities. Low amounts of the hydrophobe are required to enhance viscosity by orders of magnitude. Also, very high viscosities can be obtained using relatively low polymer concentrations. 2.5.2.2. Effect of polymer molecular weight. Bock et Ž1 9 8 9 . a l. e x a m in e d th re e Noctylacrylamideracrylamide copolymers with degree of hydrolysis of 18% and intrinsic viscosities of 2.0, 7.6, and 8.4 dlrg, respectively. These polymers were prepared in 2 mass% sodium chloride solution. At a given polymer concentration, increasing the intrinsic viscosity Žtherefore molecular weight. resulted in higher viscosity. This trend is similar to that observed for nonassociating water-soluble polymers. 2.5.2.3. Effect of hydrophobe content and type. Bock et al. Ž1989. examined the effect of hydrophobe content and structure on the viscosity of associating polymers. For a given hydrophobe type, increasing the hydrophobe content resulted in higher viscosity. Introducing a phenyl group in the hydrophobe monomer significantly enhanced the viscosity, especially at high hydrophobe contents. 2.5.2.4. Effect of shear rate. The flow curves Žapparent viscosity as a function of shear rate. of polymer will change because of hydrophobic association. Regions of both shear-thinning and shear-thickening behaviour have been observed with 0.75 mol% N-octylacrylamideracrylamide copolymer ŽBock et al., 1988a.. At polymer concentrations greater than 3000 ppm the apparent viscosity is constant at low shear rate, then increases with shear rate Žshear thickening. up to a maximum, and finally decreases with increasing shear rate Žshear thinning.. This unique and complex behaviour is due to shifting the relative amount of inter and intramolecular association with shear rate ŽBock et al., 1988a.. One possible expla-

nation for the shear thickening behaviour is that the polymer chains are stretched at high shear rates. This will enhance intermolecular association and, as a result, the viscosity increases. This transient behavior has been studied in detail by Klucker et al. Ž1995.. 2.5.2.5. Effect of temperature. McCormick et al. Ž1988. examined the effect of temperature on the viscosity of a copolymer of acrylamide and N-decylacrylamide. They found that the reduced viscosity of the copolymer increased with temperature, while that of the polyacrylamide remained constant. This result indicates that interchain association is favored by an increase in temperature. One explanation for this trend is that hydrophobe–hydrophobe association is endothermic. 2.5.3. Effect of chemical interactions on the rheological properties of associating polymers Bock et al. Ž1988a. examined the effect of salts on the viscosity of N-octylacrylamideracrylamide copolymer in water and 2 mass% sodium chloride. The viscosity of the associating polymer increased in the presence of salts, especially at higher polymer concentrations. This trend can be explained as follows. The hydrophobic groups associate to minimize their exposure to water. This is similar to micelle formation encountered with ionic surfactant solutions. Increasing salinity enhances aggregation and reduces the critical micelle concentration. Similarly, the effect of salts on viscosity of associating polymers can be attributed to association. Similar trends were obtained by McCormick et al. Ž1988. using a copolymer of acrylamide and decylacrylamide. One major disadvantage of partially hydrolyzed polyacrylamide is its high sensitivity to salts ŽNasrEl-Din et al., 1991.. This is not so for hydrophobically associating polyacrylamides. The hydrolyzed copolymer of N-octylacrylamider acrylamide had a reduced sensitivity to salts when compared to partially hydrolyzed polyacrylamide, especially at higher hydrophobe contents ŽBock et al., 1988a.. Surfactant concentration Žvaried after polymerization. greatly affects viscosity of associating polymer systems. Iliopoulos et al. Ž1991. and Magny et al. Ž1992. studied the interactions between sodium dodecyl sulfate ŽSDS. and hydrophobically modified polyŽsodium acrylate. with 1 or 3 mol% of octadecyl

K.C. Taylor, H.A. Nasr-El-Dinr Journal of Petroleum Science and Engineering 19 (1998) 265–280

or dodecyl associating groups. A viscosity maximum occurred at a surfactant concentration close to or lower than the critical micelle concentration ŽCMC.. Viscosity increases of up to 5 orders of magnitude were observed. Glass et al. Ž1990. observed similar behaviour with hydrophobically modified HEC polymers. The low-shear viscosity of hydrophobically modified HEC showed a maximum at the CMC of sodium oleate. At the critical micelle concentration, the micelles can effectively cross-link the associating polymer if more than one hydrophobic group from different polymer chains is incorporated into a micelle. Above the CMC, the number of micelles per polymer-bound hydrophobe increases, and the micelles can no longer effectively cross-link the polymer. As a result, viscosity diminishes. Theoretical models of associating polymers and their interaction with nonionic surfactants have been reviewed by Balazs et al. Ž1993.. Hydrophobic polymer–surfactant interactions have been reviewed by Goddard Ž1991. and Piculell et al. Ž1996.. 2.6. Flow in porous media The flow of associating polymers through porous media has been reported in the patent literature ŽLandoll, 1984; Bock et al., 1987b,d; Evani, 1989.. Bock et al. Ž1987d. examined copolymers of acrylamide with the sulfonate monomer AMPS and N-octylacrylamide. They claim that hydrophobe levels that are too high can lead to polymer adsorption and plugging, but that sulfonate groups in the polymer reduce the level of adsorption of polymer in Berea sandstone. Bock et al. studied the mechanical stability and resistance factors of some associating polymers ŽBock et al., 1987b,d.. The resistance factor is defined as follows: Rs

D Ppolymer D P brine

Ž 3.

where D P is the pressure drop across the core and the flow rate is constant. Solutions containing 1500 ppm of polymer in brine Ž3 mass% sodium chloride and 0.3 mass% calcium chloride. were passed through a 500 md Berea sandstone disk at varying flow velocities. Viscosities of the produced polymer solutions were determined at a shear rate of 11 sy1 .

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Commercial HPAM lost 50% of its viscosity at a flow velocity of 50 ftrday. Associating polymers containing AMPS maintained at least 50% of their viscosity up to 1000 ftrday, while associating polymers containing NVP maintained 50% of their viscosity at 675 ftrday. All of the associating polymers contained 0.75 mol% N-octylacrylamide. The NVP associating polymer contained 30 mol% NVP and had an intrinsic viscosity of 6.4 dlrg in 2 mass% NaCl. With the same coreflood experiments, Bock et al. Ž1987b,d. measured the resistance factor Ž R . of associating and conventional polymers. The associating polymers have much higher resistance factors at flow velocities of 1 ftrday, which is typical of reservoir flow away from the wellbore area. These polymers also exhibit a drop in resistance factor as flow rate increases, which is desirable. The commercial HPAM showed a maximum resistance factor at about 10 ftrday, after which the value dropped due to shear degradation of the polymer. Evani Ž1989. examined the behaviour of associating copolymers of acrylamideracrylic acidrdodecyl methacrylate. Resistance factors of these polymers were measured in Berea sandstone cores 2.54 cm long by 2.54 cm in diameter. Brine permeabilities ranged from 150 to 300 md. Polymer concentrations of 500 ppm in 3 mass% sodium chloride were used. Associating polymers with 0.1 mol% dodecyl methacrylate, 25% degree of hydrolysis and intrinsic viscosities of 13 dlrg Ž3 mass% NaCl. were among those examined. At two ftrday, resistance factors of 20 to 30 were measured, while that of HPAM was about eight. The resistance factor of the associating polymers decreased slightly up to 50 ftrday, while the resistance factor of HPAM increased. Uhl et al. Ž1993. found that acrylamide-based associating polymers developed higher solution viscosities and screen factors than Cyanatrol 960 Ža commercial HPAM. in 0.5 to 30 mass% NaCl brines, and that they had better injectivity due to their shear-thinning characteristics. Screen factor is measured by passing a solution through a stack of screens of defined size, and calculating the ratio of flow times with polymer and without polymer ŽFoshee et al., 1976.. Acrylamiderdodecyl methacrylate copolymers increased the viscosity of 15% hydrochloric acid and

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50% phosphoric acid, as compared to an equivalent molecular weight PAM, after overnight dissolution. Viscosities as much as 250 times greater than the control were obtained ŽEvani, 1989.. This suggests that these polymers could be effective in the acid treatment of carbonate reservoirs. Landoll Ž1984. conducted corefloods with hydrophobically modified hydroxyethyl cellulose. The degree of molar substitution of HEC was 2.5 and n-hexadecyl groups were present at either 0.4 or 0.9 mass%. Solutions containing 1000 ppm polymer in brine Ž2 mass% sodium chloride with 0.2 mass% calcium chloride. were flowed through a fired Berea sandstone core at a flow velocity of 11 ftrday. With 0.9 mass% n-hexadecyl groups, a resistance factor of 75 and a residual resistance factor of 23 were obtained. In contrast, the residual resistance factor of unmodified HEC was 1.0. Residual resistance factor measures the increased pressure drop across a core due to polymer retention. Brine without polymer is injected into a core after a polymer injection, and the stabilized pressure drop is measured. This pressure drop is divided by the pressure drop obtained at the same flow rate of brine before polymer injection. 3. Concluding remarks Ž1. Synthesis of acrylamide-based associating polymers is very similar to polyacrylamide synthesis. However, micellar polymerization is generally required to incorporate both water and oil soluble monomers into the polymer. The amount and type of surfactant present during micellar polymerization affect the properties of the resulting polymer. Ž2. Characterization of the hydrophobic interactions of the resulting polymers is possible using fluorescence techniques. Ž3. Rheological properties of associating polymers are affected by hydrophobe type and content, by molecular weight, degree of hydrolysis, temperature, salinity and by the presence of surfactants. Ž4. The hydrolytic stability of associating polymers containing N-alkylacrylamide hydrophobic groups is similar to partially hydrolyzed polyacrylamide. Stability can be improved by incorporating N-vinyl-2-pyrrolidinone ŽNVP. or the sulfonate monomer AMPS into the polymer during polymerization.

Ž5. Associating polymers have been reported which are shear-stable at flow rates of up to 1000 ftrday in Berea sandstone. They showed resistance and residual resistance factors much greater than conventional polyacrylamides, and did not exhibit any injectivity problems.

4. Nomenclature

h h0 wh x AIBN AMPS

viscosity of polymer solution ŽmPa P s. solvent viscosity ŽmPa P s. intrinsic viscosity Ždlrg. 2,2X-azobisŽ2-methylpropionitrile. 2-acrylamido-2-methyl-1-propanesulfonic acid c polymer concentration Žgrdl. ) c critical aggregation concentration ŽCAC. Žgrdl. CMC critical micelle concentration Žgrdl. EOR enhanced oil recovery HEC hydroxyethyl cellulose HEUR hydrophobically modified ethoxylated urethane HLB hydrophile-lipophile balance HPAM partially hydrolyzed polyacrylamide HPC hydroxypropyl cellulose I initiator concentration Žmolar. IOR improved oil recovery k Huggins constant M total monomer concentration Žmolar. Mw polymer weight average molecular weight Žgrmol. NIS nonionic surfactant NVP N-vinyl-2-pyrrolidinone PAM polyacrylamide Žunhydrolyzed. R resistance factor SDS sodium dodecyl sulfate TEA triethylamine

Acknowledgements The authors would like to thank Wendy Faid and Lynne Story, I.N. McKinnon Memorial Library, for their help in conducting literature searches and in obtaining most of the papers and patents reviewed.

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The authors also thank the Petroleum Recovery Institute, Saudi Aramco and the Saudi Arabian Ministry of Petroleum and Minerals for permission to publish this work. References Aharoni, S.M., 1978. Critical concentrations for intermolecular interpenetration and entanglements. J. Macromol. Sci. Phys. B 15 Ž3., 347–370. Beihoffer, T.W., Lundberg, D.J., Glass, J.E., 1989. Influence of polarity in water-soluble polymer synthesis. In: Glass, J.E. ŽEd.., Polymers in Aqueous Media, Performance Through Association. Advances in Chemistry Series No. 223, American Chemical Society, Washington, DC, pp. 151–164. Balazs, A.C., Huang, K., Pan, T., 1993. Modeling of amphiphilic polymers and their interactions with nonionic surfactants. Coll. Surf. A: 75, 1–20. Bhattacharyya, B.R., St. John, M.R., 1991. Hydrophobic Cationic Terpolymers from Acrylamide, Unsaturated Quaternary Salt and Vinyl Acetate. U.S. Pat. 5,068,297. Biggs, S., Hill, A., Candau, F., 1992. Copolymerization of acrylamide and a hydrophobic monomer in an aqueous micellar medium: Effect of the surfactant on the copolymer microstructure. J. Phys. Chem. 96, 1505–1511. Bock, J., Jacques, D.F., Valint, P.L., Jr., Pacansky, T.J., Yang, H.W.-H., 1987a. Hydrophobically functionalized Cationic Polymers. European Patent Application Number 87307925.5, Publication Number 0 260 108. Bock, J., Pace, S.J., Schulz, D.N., 1987b. Enhanced Oil Recovery with Hydrophobically Associating Polymers containing Nvinyl Pyrrolidone Functionality. U.S. Pat. 4,709,759. Bock, J., Siano, D.B., Valint, P.L. Jr., Pace, S.J., 1987c. Structure and properties of hydrophobically associating polymers. Polym. Mater. Sci. Eng. 57, 487–491. Bock, J., Siano, D.B., Valint, P.L., Jr., Pace, S.J., 1989. Structure and properties of hydrophobically associating polymers. In: Glass, J.E. ŽEd.., Polymers in Aqueous Media: Performance through Association. Advances in Chemistry Series No. 223, American Chemical Society, Washington, DC, pp. 411–424. Bock, J., Siano, D.B., Pace, S.J., 1992. Enhanced Oil Recovery with Hydrophobically Associating Polymers. Canadian Patent 1,300,362. Bock, J., Valint, P.L., 1988. Process for Preparing Hydrophobically Associating Terpolymers Containing Sulfonate Functionality. U.S. Pat. 4,730,028. Bock, J., Valint, P.L., Pace, S.J., 1987d. Enhanced Oil Recovery with Hydrophobically Associating Polymers containing Sulfonate Functionality. U.S. Pat. 4,702,319. Bock, J., Valint, P.L., Jr., Pace, S.J., Siano, D.B., Schulz, D.N., Turner, S.R., 1988a. Hydrophobically associating polymers. In: Stahl, G.A., Schulz, D.N. ŽEds.., Water-soluble Polymers for Petroleum Recovery. Plenum Press, New York, pp. 147– 160. Bock, J., Valint, P.L., Pace, S.J., Schulz, D.N., 1988b. Enhanced Oil Recovery Process. UK Patent Application GB 2199354A.

277

Bock, J., Varadaraj, R., Schulz, D.N., Maurer, J.J., 1994. Solution properties of hydrophobically associating water-soluble polymers. In: Dubin, P. ŽEd.., Macromol. Complexes Chem. Biol. Springer-Verlag, Berlin, pp. 33–50. Chatterji, J., Borchardt, J.K. hard, 1981. Applications of watersoluble polymers in the oil field. J. Pet. Technol. 33, 2042– 2056. Ching, T.Y., 1987. Surfactant-containing Water Thickening Polymer. UK Patent Application GB 2179048A. Constien, V.G., King, M.T., 1985. Hydraulic Fracturing Process and Compositions. U.S. Pat. 4,541,935. Dersch, R., 1994. Associative thickeners past present and future. Surf Coat. Aust. 31 Ž5., 18–22. Dubin, P.L., Strauss, U.P., 1970. Hydrophobic bonding in alternating copolymers of maleic acid and alkyl vinyl ethers. J. Phys. Chem. 74 Ž14., 2842–2847. Dubin, P., Strauss, U.P., 1967. Hydrophobic hypercoiling in copolymers of maleic acid and alkyl vinyl ethers. J. Phys. Chem. 71 Ž8., 2757–2759. Emmons, W.D., Stevens, T.E., 1983. Acrylamide Copolymer Thickener for Aqueous Systems. U.S. Pat. 4,395,524. Evani, S., 1982. Water-dispersible Hydrophobic Thickening Agent. European Patent Application 0 057 875 A2. Evani, S., 1984. Water-dispersible Hydrophobic Thickening Agent. U.S. Pat. 4,432,881. Evani, S., 1989. Enhanced Oil Recovery Process using a Hydrophobic A ssociative Com position containing a Hydrophilicrhydrophobic Polymer. U.S. Pat. 4,814,096. Evani, S., Corson, F.P., 1976. Vinyl Benzyl Ethers and Nonionic Water Soluble Thickening Agents prepared therefrom. U.S. Pat. 3,963,684. Evani, S., Corson, F.P., 1978. Aqueous Polymeric Thickening Agents. U.S. Pat. 4,105,649. Evani, S., Rose, G.D., 1987. Water soluble hydrophobe association polymers. Polym. Mater. Sci. Eng. 57, 477–481. Evani, S., van Phung, K., 1985. Hydrophobic Associative Composition containing a Polymer of a Water-soluble Monomer and an Amphiphilic Monomer. International Patent WO 85r03510. Flynn, C.E., Goodwin, J.W., 1991. Association of acrylamidedodecylmethacrylate copolymers in aqueous solution. In: Schulz, D.N., Glass, J.E. ŽEds.., Polymers as Rheology Modifiers. ACS Symposium Series No. 462, American Chemical Society, Washington, DC, pp. 190–206. Fong, D.W., 1991. Synthesis of Hydrophobicralkoxylated Polymers. U.S. Pat. 5,075,390. Foshee, W.C., Jennings, R.R., West, T.J., 1976. Preparation and Testing of Partially Hydrolyzed Polyacrylamide Solutions. SPE 6202, 51st Annu. SPE Fall Conf. New Orleans, LA, USA. Glass, J.E., Karunasena, A., 1989. Associative thickeners: From nonsense to reality. Polym. Mater. Sci. Eng. 61, 145–152. Glass, J.E., Lundberg, D.J., Ma, Z. Ka, Karunasena, A., Brown, R.G., 1990. Viscoelasticity and high shear rate viscosity in associative thickener formulations. Proc. Water-Borne Higher-Solids Coat. Symp. 17, 102–120. Goddard, E.D., 1991. On polymerrsurfactant interaction. In: Mittal, K.L., Shah, D.O. ŽEds.., Surfactants in Solution, vol. 11. Plenum Press, New York, pp. 219–242.

278

K.C. Taylor, H.A. Nasr-El-Dinr Journal of Petroleum Science and Engineering 19 (1998) 265–280

Goodwin, J.W., Hughes, R.W., Lam, C.K., Miles, J.A. and Warren, B.C.H., 1989. The rheological properties of a hydrophobically modified cellulose. In: Glass, J.E. ŽEd.., Polymers in Aqueous Media: Performance through Association. Advances in Chemistry Series No. 223, American Chemical Society, Washington, DC, pp. 365–378. Hawe, M., 1993. The development and properties of associative thickeners. Nord. Pulp Pap. Res. J. 8 Ž1., 188–190. Hill, A., Candau, F., Selb, J., 1991. Aqueous solution properties of hydrophobically associating copolymers. Progr. Colloid Polym. Sci. 84, 61–65. Hill, A., Candau, F., Selb, J., 1993. Properties of hydrophobically associating polyacrylamides: Influence of the method of synthesis. Macromolecules 26, 4521–4532. Iliopoulos, I., Wang, T.K., Audebert, R., 1991. Viscometric evidence of interactions between hydrophobically modified polyŽsodium acrylate. and sodium dodecyl sulfate. Langmuir 7 Ž4., 617–619. Jacques, D.F., Bock, J., 1988. Hydrophobically associating Polymers for Oily Water clean-up. U.S. Pat. 4,734,205. King, M.T., Constien, V.G., 1986. Rheology characterization of a novel hydrophobic association polymer. Polym. Mater. Sci. Eng. 55, 869–874. Klucker, R., Candau, F., Schosseler, F., 1995. Transient behavior of associating copolymers in a shear flow. Macromol. 28, 6416–6422. Landoll, L.M., 1982. Nonionic polymer surfactants. J. Polym. Sci. Polym. Chem. Ed. 20, 443–455. Landoll, L.M., 1984. Method for Enhanced Oil Recovery. South Africa Pat. ZA 8304193. Landoll, L.M., 1985. Hydrophobically Modified Polymers. U.S. Pat. 4,529,523. Littman, W., 1988. Polymer Flooding: Developments in Petroleum Science, No. 24. Elsevier, Amsterdam. MacWilliams, D.C., Rogers, J.H., West, T.J., 1973. Water-soluble polymers in petroleum recovery. In: Bikales, N.M. ŽEd.., Water-soluble Polymers, Polymer Science and Technology, vol. 2. Plenum Press, New York, pp. 105–225. Magny, B., Iliopoulos, I., Audibert, R., 1991. Intrinsic viscosity of hydrophobically modified polyelectrolytes. Polym. Commun. 32 Ž15., 456–458. Magny, B., Iliopoulos, I., Audebert, R., Riculell, L., Lindman, B., 1992. Interactions between hydrophobically modified polymers and surfactants. Progr. Coll. Polym. Sci. 89, 118–121. Maurer, J.J., Schulz, D.N., Bock, J., 1986. Process for the formation of novel acrylamide acrylate copolymers. U.S. Pat. 4,579,926. McCormick, C.L., Bock, J., Schulz, D.N., 1989. Water-soluble polymers. In: Encyclopedia of Polymer Science and Engineering, 2nd ed., vol. 17. John Wiley and Sons, New York, pp. 730–784. McCormick, C.L., Branham, K.D., Davis, D.L., Middleton, J.C., 1993. A new generation of electrolyte and pH responsive water-soluble polymers for mobility control. Prep. Am. Chem. Soc. Div. Pet. Chem. 38 Ž1., 146–149. McCormick, C.L., Hester, R.D., 1990. Polymers for Mobility Control in Enhanced Oil Recovery. U.S. Dept. of Energy, Report DOErBCr10844-20.

McCormick, C.L., Johnson, C.B., 1988. Structurally tailored macromolecules for mobility control in enhanced oil recovery. In: Stahl, G.A., Schulz, D.N. ŽEds.., Water-Soluble Polymers for Petroleum Recovery. Plenum Press, New York, pp. 161– 180. McCormick, C.L., Johnson, C.B., 1989. Synthetically structured water-soluble copolymers: Associations by hydrophobic or ionic mechanisms. In: Glass, J.E. ŽEd.., Polymers in Aqueous Media: Performance through Association. Advances in Chemistry Series No. 223, American Chemical Society, Washington, DC, pp. 437–454. McCormick, C.L., Nonaka, T., Johnson, C.B., 1988. Water-soluble copolymers. 27. Synthesis and aqueous solution behaviour of associative acrylamider n-alkylacrylamide copolymers. Polymer 29 Ž4., 731–739. Middleton, J.C., Cummins, D.F., McCormick, C.L., 1991. Rheological properties of hydrophobically modified acrylamidebased polyelectrolytes. In: Shalaby, S.W., McCormick, C.L., Butler, G.B. ŽEds.., Water-Soluble Polymers: Synthesis, Solution Properties and Applications. ACS Symposium Series No. 467, American Chemical Society, Washington, DC, pp. 338– 348. Nasr-El-Din, H.A., Hawkins, B.F. and Green, K.A., 1991. Viscosity behavior of alkaline, surfactant, polyacrylamide solutions used for enhanced oil recovery. SPE 21028, Proc. Int. Symp. Oilfield Chem., Anaheim, CA, USA. Nasr-El-Din, H.A., Noy, J.L., 1992. Flow behaviour of alkaline, surfactant and xanthan solutions used for enhanced oil recovery. Rev. Inst. Fr. Petr. 47 Ž6., 771–791. Needham, R.B., Doe, P.H., 1987. Polymer flooding review. J. Pet. Technol. 39 Ž12., 1503–1507. Peiffer, D.G., 1989. Cationic-hydrogen bonding type hydrophobically associating copolymers. U.S. Pat. 4,847,342. Peiffer, D.G., 1990. Hydrophobically associating polymers and their interactions with rod-like micelles. Polymer 31, 2353– 2360. Peiffer, D.G., 1991. Cationic Hydrophobic Monomers and Polymers. U.S. Pat. 5,071,934. Peiffer, D.G., Bock, J., Elward-Berry, J., 1992. Thermally stable hydrophobically associating Rheological Control Additives for Water-based Drilling Fluids. U.S. Pat. 5,096,603. Peiffer, D.G., Kaladas, J.J., 1990. N-Sulfoalkyl Polyamide watersoluble hydrophobically-associating rigid rod Polymer. U.S. Pat. 4,894,422. Piculell, L., Guillemet, F., Thuresson, K., Shubin, V., Ericsson, O., 1996. Binding of surfactants to hydrophobically modified polymers. Adv. Coll. Interface Sci. 63, 1–21. Sau, A.C., Landoll, L.M., 1989. Synthesis and solution properties of hydrophobically modified Žhydroxyethyl.cellulose. In: Glass, J.E. ŽEd.., Polymers in Aqueous Media: Performance through Association. Advances in Chemistry Series No. 223, American Chemical Society, Washington, DC, pp. 343–364. Schulz, D.N., 1991. Water-soluble polymer synthesis: Theory and practice. In: Shalaby, S.W., McCormick, C.L. and G.B. Butler ŽEds.., Water-Soluble Polymers: Synthesis, Solution Properties and Applications. ACS Symposium Series No. 467, American Chemical Society, Washington, DC, pp. 57–73. Schulz, D.N., Bock, J., 1991. Synthesis and fluid properties of

K.C. Taylor, H.A. Nasr-El-Dinr Journal of Petroleum Science and Engineering 19 (1998) 265–280 associating polymer systems. J. Macromol. Sci. Chem. A 28 Ž11–12., 1235–1243. Schulz, D.N., Berluche, E., Maurer, J.J., Bock, J., 1987a. Tetrapolymers of N-vinyl pyrrolidoneracrylamidersalt of acrylic acidr n-alkyl acrylamide. U.S. Pat. 4,663,408. Schulz, D.N., Berluche, E., Maurer, J.J., Bock, J., 1988a. Novel Acrylamide Acrylate Copolymers. U.S. Pat. 4,792,593. Schulz, D.N., Bock, J., Valint, P.L., Jr., 1994. Synthesis and characterization of hydrophobically associating water-soluble polymers. In: Dubin, P. ŽEd.., Macromol. Complexes Chem. Biol. Springer-Verlag, Berlin, pp. 3–13. Schulz, D.N., Duvdevani, I., Bock, J., Berluche, E., 1987b. Terpolymers of Acrylamide, Alkylacrylamide and Betaine Monomers. U.S. Pat. 4,650,848. Schulz, D.N., Duvdevani, I., Bock, J., Kaladas, J.J., 1988b. Terpolymers of Acrylamide, Alkyl Polyetheroxyacrylate and Betaine Monomers. U.S. Pat. 4,788,247. Schulz, D.N., Kaladas, J.J., Maurer, J.J. .B, Bock, J., Pace, S.J., Schulz, W.W., 1987c. Copolymers of acrylamide and surfactant macromonomers: Synthesis and solution properties. Polymer 28 Ž12., 2110–2115. Schulz, D.N., Maurer, J.J., Bock, J., 1984. Process for the Formation of Novel Acrylamide Acrylate Copolymers. U.S. Pat. 4,463,151. Schwab, F.C., Sheppard, E.W., Chen, C.S.H., 1978. Waterflooding Process Employing Cationic-nonionic Copolymers. U.S. Pat. 4,110,232. Shay, G.D., Kravitz, F.K., 1987. Nonionic Associative Thickeners. European Patent Application: 0 250 943 A2. Shay, G.D., Kravitz, F.K., 1988. Nonionic Associative Thickeners. U.S. Pat. 4,722,962. Siano, D.B., Bock, J., 1987. High Molecular Weight Terpolymers of Acrylamide, Acrylic Acid Salts and Alkylacrylamide. U.S. Pat. 4,694,058. Siano, D.B., Bock, J., Myer, P., Valint, P.L., Jr., 1989. Fluorescence and light scattering from water-soluble hydrophobically associating polymers. In: Glass, J.E. ŽEd.., Polymers in Aqueous Media: Performance through Association. Advances in Chemistry Series No. 223, American Chemical Society, Washington, DC, pp. 425–435. Sorbie, K.S., 1991. Polymer-Improved Oil Recovery. CRC Press, Boca Raton, Florida. Stanley, F.W., Jr., 1985. Water-in-Oil Emulsions of Hydrophobe Association Polymers. U.S. Pat. 4,524,175. Strauss, U.P., Jackson, E.G., 1951. Polysoaps. I. viscosity and solubilization studies on an n-dodecyl bromide addition compound of poly-2-vinylpyridine. J. Polym. Sci. 6 Ž5., 649–659. Sutherland, I.W., Kierulf, C., 1987. Downhole use of Biopolymers. Proc. Inst. Pet., London, First Microb. Probl. Off Shore Oil Industry, pp. 93–103. Turner, S.R., Siano, D.B., Bock, J., 1985a. Microemulsion Process for Producing Acrylamide-Alkyl Acrylamide Copolymers. U.S. Pat. 4,521,580. Turner, S.R., Siano, D.B., Bock, J., 1985b. Micellar Process for the Production of Acrylamide-alkyl Acrylamide Copolymers. U.S. Pat. 4,528,348. Turner, S.R., Siano, D.B., Bock, J., 1985c. Acrylamide-Alkylacrylamide copolymers. U.S. Pat. 4,520,182.

279

Uhl, J.T., Ching, T.Y., Bae, J.H., 1993. A laboratory study of new, surfactant-containing polymers for high-salinity reservoirs. SPE 26400, Proc. 68th Ann. Tech. Conf. and Exhib. of Soc. Pet. Eng., Houston, TX, USA. Valint, P.L. Jr., Bock, J., 1988. Synthesis and characterization of hydrophobically associating block polymers. Macromolecules 21 Ž1., 175–179. Valint, P.L., Bock, J., 1992. Hydrophobically associating Terpolymers containing Sulfonate Functionality. U.S. Pat. 5,089,578. Valint, P.L. Jr., Bock, J., Schulz, D.N., 1987. Synthesis and characterization of hydrophobically associating polymers. Polym. Mater. Sci. Eng. 57, 482–486. Valint, P.L., Jr., Bock, J., Schulz, D.N., 1989. Synthesis and Characterization of Hydrophobically Associating Polymers. In: Glass, J.E. ŽEd.., Polymers in Aqueous Media: Performance through Association. Advances in Chemistry Series No. 223, American Chemical Society, Washington, DC, pp. 399–410. van Phung, K., Evani, S., Hydrophobe Associative Composition containing a Polymer of a Water-soluble Monomer and an Amphiphilic Monomer. Eur. Pat. Appl. 0226097986 A2. van Phung, K., Evani, S., 1988. Amphiphilic Monomer and Hydrophobe Associative Composition containing a Polymer of a Water-soluble Monomer and said Amphiphilic Monomer. U.S. Pat. 4,728,696. Varadaraj, R., Bock, J., Brons, N., Pace, S. 199, 1993. Probing hydrophobic microdomains of hydrophobically associating acrylamide-n-alkylacrylamide copolymers in solution using a solvatochromic absorption dye probe. J. Phys. Chem. 97, 12991–12994. Varadaraj, R., Branham, K.D., McCormick, C.L., Bock, J., 1994. Analysis of hydrophobically associating copolymers utilizing spectroscopic probes and labels. In: Dubin, P. ŽEd.., Macromol. Complexes Chem. Biol. Springer-Verlag, Berlin, pp. 15–31. Wang, Y., Winnik, M.A., 1990. Onset of aggregation for watersoluble polymeric associative thickeners: A fluorescence study. Langmuir 6 Ž9., 1437–1439. Wang, T.K., Iliopoulos, I., Audebert, R., 1991. Aqueous-solution behavior of hydrophobically modified polyŽacrylic acid.. In: Shalaby, S.W., McCormick, C.L., Butler, G.B. ŽEds.., WaterSoluble Polymers: Synthesis, Solution Properties and Applications. ACS Symposium Series No. 467, American Chemical Society, Washington, DC, pp. 218–231. Wang, K.T., Illiopoulos, I., Audebert, R., 1988. Viscometric behaviour of hydrophobically modified polyŽsodium. acrylate. Polym. Bull. 20, 577–582. Winnik, F.M., Ringsdorf, H., Venzmer, J., 1991b. Interactions of surfactants with hydrophobically modified polyŽ n-isopropylacrylamides.. 2. Fluorescence label studies. Langmuir 7 Ž5., 912–917. Winnik, F.M., Ringsdorf, H., Venzmer, J., 1991a. Interactions of surfactants with hydrophobically modified polyŽ n-isopropylacrylamides.. 1. Fluorescence probe studies. Langmuir 7 Ž5., 905–911. Wolff, C., 1977. Molecular weight dependence of the relative viscosity of solutions of polymers at the critical concentration. Eur. Polym. J. 13, 739–741. Yang, H.W., Pacansky, T.J., 1990. Inverse Emulsion Process for

280

K.C. Taylor, H.A. Nasr-El-Dinr Journal of Petroleum Science and Engineering 19 (1998) 265–280

preparing Hydrophobe-containing Polymers. U.S. Pat. 4,918,123. Yen, W.S., Coscia, A.T., Kohen, S.I., 1989. Polyacrylamides. In: Donaldson, E.C., Chilingarian, G.V., Yen T.F. ŽEditors., Enhanced Oil Recovery, II: Processes and Operations ŽDevelopments in Petroleum Science, 17B.. Elsevier Science Publishers, pp. 189–218. Zaitoun, A., Potie, B., 1983. Limiting conditions for the use of hydrolyzed polyacrylamides in brines containing divalent ions. SPE 11785, Int. Symp. Oilfield Geothermal Chem., Denver, CO, USA. Zhang, Y.-X., Da, A.-H., Hogen-Esch, T.E., 1990. A fluorocarbon-containing hydrophobically associating polymer. J. Polym. Sci. Part C:. 28 Ž7., 213–218.

Zhang, Y.-X., Da, A.-H., Hogen-Esch, T.E. and Butler, G.B., 1991. New fluorocarbon-containing hydrophobially associating polyacrylamide copolymer. In: Shalaby, S.W., McCormick, C.L., Butler, G.B., ŽEds.., Water-Soluble Polymers: Synthesis, Solution Properties and Applications. ACS Symposium Series No. 467, American Chemical Society, Washington, DC, pp. 159–174. Zhang, Y.-X., Da, A.-H., Butler, G.B., Hogen-Esch, T.E., 1992. A fluorine-containing hydrophobically associating polymer. I. Synthesis and solution properties of copolymers of acrylamide and fluorine-containing acrylates or methacrylates. J. Polym. Sci. Part A 30, 1383–1391.