Study on the Mobilization Mechanisms of Microscopic Residual Oil in High-Water-Cut Sandstone Reservoirs

Abstract

As mature oilfields enter the high-water-cut development stage, significant amounts of residual oil remain trapped underground. To enhance the effectiveness of tertiary oil recovery, it is crucial to understand the distribution and mobilization patterns of this residual oil. In this study, polydimethylsiloxane (PDMS) was used to create a microscopic oil displacement model, which was observed and recorded using a stereomicroscope. The experimental images were extracted, analyzed, and quantitatively evaluated, categorizing the microscopic residual oil in the high-water-cut sandstone reservoirs of Dagang Oilfield into cluster-like, pore surface film-like, corner-like, and slit-like types. Polymer–surfactant composite flooding (abbreviated as SP flooding) effectively mobilized 47.16% of cluster-like residual oil and 43.74% of pore surface film-like residual oil, with some mobilization of corner-like and slit-like residual oil as well. Building on SP flooding, dual-mobility flooding further increased the mobilization of cluster-like residual oil by 12.37% and pore surface film-like residual oil by 3.52%. With the same slug size, dual-mobility flooding can reduce development costs by 16.43%. Overall, dual-mobility flooding offers better development prospects.