Water-Soluble Hydrophobically Associating Polymers for Improved Oil Recovery: A Literature Review

Abstract

SPE Members Abstract Water-soluble hydrophobic ally associating polymers are reviewed with particular emphasis on their application in 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. Introduction Water-soluble polymers are used in many oilfield operations including drilling, polymer-augmented water flooding, chemical flooding and profile modification. 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 fluids are desired that can suspend 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 (IOR) has been extensively reviewed. Commercially, both partially hydrolyzed polyacrylamide (HPAM) and biopolymers (such 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 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. High molecular weights, however, are required to produce high viscosities at low concentrations. P. 675