New Insights into the Mechanism of Mobility Reduction by Associative Type Copolymers

Abstract

Abstract New thickeners based on associative properties and their application in enhanced oil recovery are discussed. The new thickeners are anionic, water-soluble, hydrophobically modified copolymers. The rheological properties as well as the flow properties in porous media have been evaluated. In bulk the polymer viscosity is shear thinning and the viscosity vs. shear rate profile is comparable with other synthetic EOR polymers. For most of the other tested parameters, the new thickeners differ from what is assumed as the standard properties for EOR polymers. The relative viscosity increases by increasing the temperature, especially at low shear rates. The core flood experiments revealed a significant mobility reduction in sandstone cores, both at ambient and elevated temperature. The mobility reduction demonstrated strongly shear thinning behavior. For standard EOR polymers the main contribution to the mobility reduction and improved mobility ratio is the polymer viscosity, while for the new thickeners the mobility reduction seems to be dominated by reversible polymer retention that is lowering the permeability. Post water injection resulted in low permeability reduction. However, the time to regain the permeability was significant. Flood experiments with the associative polymer in Bentheim sandstone cores showed significantly increased oil production. The incremental oil recovery was interpreted by the capillary number which due to the high mobility reduction exceeded the critical capillary number. Because of the high mobility reduction a further increase in oil production would have been possible by only slight reduction of the oil-water interfacial tension by addition of small amounts of a surfactant. Moreover the new associative polymer seems to be more shear stable than other synthetic EOR polymers.