Direct Thickeners for Mobility Control of CO2 Floods

Abstract

Abstract This paper describes efforts in an experimental search for polymers that are sufficiently soluble in dense CO2 that they could serve as mobility control agents. The operation of the apparatus designed and built for the measurement of solubility in condensed gases is described. A modified version of this apparatus has been used to measure viscosity by timing the fall of a cylinder in a tube. More than a dozen polymers have been found that are soluble at least in the parts-per-thousand (ppt) range in liquid and in dense supercritical CO2. As pressures and temperatures are varied, the solubilities of these polymers generally are found to increase with increasing CO2 density. Certain generalizations have been made concerning the influence of various polymer properties on their solubility in dense CO2. These properties include structure, stereochemistry, and molecular weight. Although the viscosity enhancements of the solutions measured thus far are insufficient for purposes of mobility control, they provide clues that point toward those features of polymer molecules that yield greater thickening properties. Also discussed are considerations involved in the application of direct thickeners in the mobility control of CO2 floods and the advantages in the use of such CO2-soluble polymers in place of methods that involve the injection of water.