Core-Based Evaluation of Associative Polymers as Enhanced Oil Recovery Agents in Oil-Wet Formations

Abstract

Linear coreflood experiments are performed at 60 °C to test the effectiveness of a low molecular weight associative polymer as a displacing agent, and its ability to enhance oil recovery on chemically treated oil-wet Berea cores. Polymer injection tests revealed high mobility reductions (resistance factor (RF)) and reduced remaining oil saturations. Results obtained suggest that the incremental oil production is due to the high mobility reduction, as reported previously for water-wet porous media. The reduced remaining oil saturation is a function of the injected associative polymer treatment volume. Polymer mobility reduction is highly affected by the injected polymer velocity; this reduction is observed to be more significant at the lower velocity spectrum. Therefore, the established incremental oil production, even at reduced polymer injection rates (lower capillary numbers), could be explained by the increased mobility reduction. A correlation for the velocity-dependent mobility reduction is developed. Results are in agreement with previously reported ones in water-wet media and related to the enhanced oil recovery (EOR) nature of the injected associative polymer as opposed to the traditional mobility control of other polymer types. During injection, a column of oil-polymer emulsion is formed gradually in the separator causing operational difficulties and introducing produced fluid measurement (and core fluid saturations) uncertainties. Produced oil/water emulsion polymer volume content is used to correct overestimated oil production attributed to measurement uncertainties. Real-time resistivity measurements could also be a valuable tool for both fluids saturation monitoring and improved core fluids saturation evaluation in flooded porous media.