Ž . Journal of Petroleum Science and Engineering 19 1998 265–280 Water-soluble hydrophobically associating polymers for improved oil recovery: A literature review Kevin C. Taylor a,1 , Hisham A. Nasr-El-Din b, ) a 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 Ž . improved oil recovery IOR . 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 modi- Ž fication Chatterji 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 en- hanced oil recovery processes. In drilling fluids, the solution rheology is very important. Shear thinning ) Corresponding author. Fax: q966-3-8762811. 1 Present address: Lab R&D Center, P.O. Box 62, Saudi Aramco, Dhahran 31311, Saudi Arabia. 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 Ž . for improved oil recovery IOR has been exten- Ž sively reviewed MacWilliams et al., 1973; Needham and Doe, 1987; Littman, 1988; Yen et al., 1989; . Sorbie, 1991 . Commercially, both partially hydrolyzed poly- Ž . Ž acrylamide HPAM and biopolymers such as xan- . than gum are used in the oil industry. These tradi- tional polymers rely on chain extension and physical entanglement of solvated chains for viscosity en- hancement. The carboxylate groups in HPAM cause chain expansion due to repulsion of the ionic groups, which leads to higher solution viscosity. The viscos- ity 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. Ž . PII S0920-4105 97 00048-X