Polymer Flood of Viscous Oils in Complex Carbonates

Abstract

Abstract Polymer flooding is investigated in laboratory cores as a non-thermal enhanced oil recovery process for viscous oils in heterogeneous carbonate reservoirs. Core floods were performed in vuggy dolomite cores saturated with 200 cP crude oil and complementary pore-scale investigations were conducted using 2D glass micromodels. Tertiary polymer floods conducted after waterfloods of a viscous oil recovered more oil than secondary polymer floods in vuggy dolomite cores as well as Berea cores. This was also observed in oil-wet dolomite cores. The oil recovery in secondary polymer floods decreased as the polymer viscosity decreased. The secondary polymer flood, of course, recovered the oil faster than tertiary polymer floods. The oil recovery was also lower and slower in oil-wet cores compared to water-wet cores. Micromodel experiments showed that the spacing between viscous fingers increases as the viscosity ratio increases. The viscous oil bypassed in waterfloods is mobile and can be recovered by a polymer flood. The waterflood recovery in a micromodel with connected heterogeneity was low, but the tertiary polymer flood recovered a significant amount of oil. Water imbibed into the low permeability bypassed regions and pulled the oil into high permeability regions which was later recoverd by the polymer flood. There was also no imbibition in oil-wet micromodels where the oil recovery was lower and slower compared to water-wet micromodels.