Microscopic Remaining Oil Distribution Regularity and Enhanced Oil Recovery Methods after Polymer Flooding

In this article, the testing data of the coring wells was analyzed to statistically summarize the variable regularity of reservoir physical parameters after polymer flooding. The laser confocal method was used to study the microscopic remaining oil distribution regularity in natural cores, and the effects of different pore structures and permeability levels on the remaining oil distribution were quantified. Both natural and artificial cores were used to compare and analyze the differences in displacement efficiency and microscopic remaining oil exploitation between different chemical flooding methods after polymer flooding. Additionally, microscopic visualization models were used to study the activation and coalescence mechanism of the remaining oil. The results showed that the permeability, washed thickness, and displacement efficiency of the reservoir after polymer flooding were significantly higher than before. After polymer flooding, the distribution characterization of the remaining oil was highly dispersed and locally enriched, and some free-state oil remained available in medium and high permeability reservoirs. The largest amount of remaining oil distribution was observed in the thinner throat reservoirs. Reservoirs with sorting coefficients of 4–6 mainly existed bound state oil. Laboratory displacement experiment results showed that ASP flooding with a higher viscosity ratio and capillary number exhibited a better oil displacement effect; the final recovery of ASP was 4.9% higher than that of a high-concentration polymer. Furthermore, ASP flooding demonstrated a stronger reduction in bound state oil compared with high-concentration polymer flooding, with an increase of 2.8%. The ASP system activates and coalesces the microscopic remaining oil after polymer flooding by high viscoelasticity, ultralow interfacial tension, wetting reversal, reduced retardation force, and emulsification.