Effect of Oil Viscosity on Heavy-Oil/Water Relative Permeability Curves

Abstract

Abstract For heavy oil reservoirs, the oil viscosity usually varies dramatically during production processes, such as thermal process or solvent injection. This paper presents an investigation of the effect of oil viscosity on relative permeability curves for heavy oil-water systems. Unsteady-state displacement tests were conducted in sandpacks under a typical injection flow rate in a heavy oil recovery process. A series of crude oils with a wide range of viscosities were used in the measurements. Large pore volumes of water were injected to minimize the errors caused by the extrapolation of the recovery data. History matching was used to obtain the relative permeability curves, in which capillary pressure was included. It was found that, for the same injection flow rate, heavy oil-water relative permeability curves systematically shifted with oil viscosity. With increasing oil viscosity, the residual oil saturation increased and the oil and water relative permeabilities decreased at the higher water saturation range. Irreducible water saturation tended to decrease with increasing oil viscosity. Micromodel experiments were conducted to visually investigate the difference in the flow behaviour between heavy oil-water and light oil-water systems. Interacting capillary bundle models were used to analyze the impact of oil viscosity on the residual oil saturation. This work aids in the laboratory measurement and determination of the representative relative permeability curves for heavy oil-water systems, as well as in the proper use of relative permeability curves in reservoir simulation for heavy oil development.