Inaccessible Pore Volume of Associative Polymer Floods

Abstract

Abstract Approximately half of current oil production is from waterfloods where a major concern is mobility control of the injected phase. Addition of polymer to the injection water decreases the mobility ratio leading to greater flood efficiency, especially for recovery of viscous oil. Of the various EOR polymer formulations, newly developed associative, water-soluble polymers show special promise. We investigate, experimentally and numerically, the inaccessible pore volume (IPV), permeability reduction (Rk), and interfacial tension characteristics of 3 different molecular weight associative polymers and, for reference, a conventional hydrolyzed polyacrylimide. Previous studies of these same associative polymers revealed good secondary and tertiary oil recovery efficiency for displacement of a viscous 140 cP oil. To our knowledge, this is the first study to observe and report IPV – Rk properties of these associative polymer solutions. New experiments were conducted by injecting polymer solutions through a roughly 12 Darcy sandpack and measuring the separation between effluent concentration profiles of the polymer and the salt used as the tracer. Results are interpreted from the effluent profiles using an analytical superposition model as well as a conventional finite difference formulation. The associative polymers yield moderate to large IPV (20 to 40%) and mild Rk (1.1 to 1.5) that increases with molecular weight. Brine salinity reduces both IPV and permeability reduction. Differences between the classical interpretation, the analytical interpretation, and the numerical implementation of IPV are discussed as is the adequacy of the conventional IPV-Rk description of the mobility control of polymer.