Pore scale and macroscopic visual displacement of oil-in-water emulsions for enhanced oil recovery

Abstract In-situ formation of emulsions has been observed in a large amount of chemical flooding pilots, and their effect on oil recovery is of great interest to petroleum engineers and researchers. In this study, microfluidic and transparent sand pack models were used to investigate mechanisms of emulsion propagation and plugging in both pore and macro scales. A microfluidic chip consisting of high- and low-permeability areas was fabricated to represent a heterogeneous area. Another chip was created with the same throat width but enlarged pore sizes (1.5 times larger) and reduced throat lengths. Two microscopic displacement experiments were conducted to compare the effect of pore structure on residual oil displacement after surfactant/polymer (SP) flooding by injecting the same emulsion slug. Meanwhile, the macroscopic flow path of the displacing fluid in the emulsion flooding was investigated using a relatively homogeneous transparent 2D sand pack. The emulsion plugging was proved to be a complicated process, and it could be strongly affected by pore throat structures. Fluid division and high oil recovery could only be achieved during the emulsion flooding in the condition with properly matched sizes of emulsion droplets and pore throats. For a relatively homogeneous 2D sand pack model, oil bank formation and enlarged sweep volume were observed in the emulsion flooding even though it was conducted after SP flooding. As suggested by results of this study, the in-situ formation of emulsion might significantly contribute to the oil recovery in reservoirs with tortuous pore structures, while making little difference in those with large pore throat channels that emulsion couldn’t be trapped in.