Pore-Scale Mechanism of Surfactant-Polymer Flooding and the Improvements on Oil Displacement Efficiency

Abstract

Abstract Many laboratory tests and field applications have successfully demonstrated that surfactant-polymer (SP) flooding is of importance and high efficiency to displace the residual oil trapped in the pores and capillaries of reservoir rock after water flooding. In this study, a micromodel experimental setup for visualized oil displacement was applied at high-temperature and high-salinity (HTHS) condition to study the synergy between a hydrophobically associating polyacrylamide (HAPAM) and different types of surfactants as mixed chemical surfactant-polymer (SP) flooding. Based on the results and captured micromodel images, the mechanisms of SP flooding to displace crude oil were investigated, and a most efficient SP flooding strategy was proposed. The physiochemical properties of the SP solutions were investigated before the micromodel displacement test. The micromodel slice was initially saturated with crude oil, followed by injections of a high-salinity water, chemical solution and subsequent water slug to displace saturated oil. During oil displacement, observed phenomena were recorded by a digital camara equipped on the micromodel device to analyze the pore-scale mechanisms of SP flooding, the viscosity alteration due to SP synergy and emulsification resulted from surfactant were also considered in the displacement mechanism. Among three surfactants, the anionic surfactant (AS) exhibited the most improved performance in oil displacement when it combined with the HAPAM comparing the other two surfactants, which is a non-ionic surfactant (NS), and a cationic surfactant (CS), respectively. The HAPAM/AS SP formulation showed a highest viscosity owning to hydrophobic association and electrostatic adsorption between HAPAM and AS comparing NS- and CS-related formulations, resulting in an enhanced sweep efficiency to displace more crude oil. Furthermore, the HAPAM/AS formulation exhibited strong emulsification to facilitate the formation of low-viscosity oil-in-water (O/W) emulsions to further enhance the flowable capacity of the crude oil, the O/W emulsion droplets can flow easily to pass through narrow throats and small or micropores by deformation along the flow, and eventually escape from the micromodel, resulting a higher displacement efficiency. Consequently, the highest production of crude oil was observed using the HAPAM/AS solution as a displacing agent comparing the other SP formulations.