Control Of Water Mobility Using Polymers and Multivalent Cations

Abstract

Abstract A newly developed process using a combination of water-soluble polymers and multivalent cations to reduce water mobility has been tested in the laboratory. The process treats the porous media with a sequence of three slugs, porous media with a sequence of three slugs, the first and third being polymer solutions and the second being a solution of a selected multivalent cation. Calcium, magnesium, and aluminum cations have been used with partially hydrolyzed polyacrylamides or copolymers of acrylamide in laboratory flow tests. For example, treatments of Repetto sandstone cores having brine permeabilities of 200 to 400 md with a polymer solution resulted in a residual resistance factor to brine of about 3; whereas, residual resistance factors of 16 to 18 were obtained by using either calcium or aluminum cations in the three-slug combination treatment with the same polymer. Based on laboratory evidence that polymer concentrations of 250 ppm can produce residual resistance factors in excess of 10 in porous media having brine permeabilities greater than 1 darcy, applications are evident in polymer flooding as well as in the high concentration-low volume treatment of oil-producing and water injection wells. These processes are being field tested in the treatment of producing wells and water injection wells to reduce water mobility and increase oil-producing rates. Introduction The action of polymers in porous media to reduce the water mobility has been extensively studied and, in general, is attributed to the increased viscosity of the polymer solution and to a reduction in permeability (residual resistance effect) to water of the porous media. For successful operations, the relative importance of these two methods of controlling mobility largely depends upon the application. In polymer flooding both methods of reducing the water mobility are important, with the permeability reduction effect probably being more permeability reduction effect probably being more significant where light oils and high variations in permeability are present. In the small volume treatment of water-injection wells to improve injection profiles and in treatment of production wells to reduce water-oil ratios, the production wells to reduce water-oil ratios, the permeability reduction effect is essential and permeability reduction effect is essential and the viscosity effect negligible. Although the various roles of polymer treatments are not clearly delineated for use with chemical flooding, the permeability reduction effect will perhaps be of dominant importance for perhaps be of dominant importance for pretreatment of reservoirs to achieve more uniform pretreatment of reservoirs to achieve more uniform injection of the chemical slug. By comparison, the viscosity effect is probably important in the slug proper, and both effects for use as a mobility buffer behind the chemical slug.