Pore-scale experimental study on EOR mechanisms of combining thermal and chemical flooding in heavy oil reservoirs

摘要

Steam flooding is an important method for the development of heavy oil reservoirs, but steam channeling is an inevitable serious problem in the process of steam injection, which decreases the sweep efficiency of steam and leads to low oil recovery. Viscosity reducer (VR) flooding and nitrogen foam flooding are two effective methods of enhancing heavy oil recovery with satisfactory results. In this paper, a series of experiments were conducted to evaluate the effects of various factors on the performance of the novel viscosity reducer (VR-A). On this basis, A visualized model was adopted to investigate the synergistic development effect of thermal and chemical flooding, which vividly reflected the interaction of chemical agents with crude oil and their migration characteristics in porous media, as well as the mechanisms of enhancing oil recovery on the pore-scale. The results showed that VR-A could achieve excellent viscosity reduction effect on heavy oil under the influence of various factors, which could be combined with thermal flooding to effectively recover heavy oil. As for the pore-scale level, after the VR-A solution was injected, the interfacial tension between the oil and water was decreased, the wettability of the surface of the particle was changed, and two types of oil-in-water emulsions (spherical emulsions and flocculent emulsions) with a lower viscosity were formed, which were easy to flow with the fluid in pores and throats and could temporarily block the high-permeability area. In the process of foam flooding, the phenomena of bubble coalescence and breakup occurred constantly, and bubbles trapped in the porous media could improve the sweep efficiency of the subsequent fluid. The ultimate oil recovery of the development method combining thermal and chemical flooding in the visualized displacement experiment is 76.9%, 39.7% higher than that of pure thermal flooding. This article can provide an effective method to solve the problem of poor steam flooding performance in heavy oil reservoirs.