Correction for capillary pressure influence on relative permeability by combining modified black oil model and Genetic Algorithm

Abstract

The substantial interference of the tight reservoir's capillary pressure on relative permeability measurement can significantly diminish the prediction accuracy of the oilfield production. This study established an innovative method to eliminate the capillary pressure effect on relative permeability calculation by combining the modified numerical simulation model and the Genetic Algorithm. Steady-state measurements were conducted on tight core sample (0.0321mD) to obtain the initial relative permeability curves using Darcy's law. A modified numerical simulation model that considers equivalent phase pressure for water and oil at outlet surface and directly simulates fixed injection-rate boundary conditions without using wells has been proposed. After analysis of water saturation distribution and pressure distribution along the core, absolute permeability, residual water saturation, and the two-phase relative permeability at corresponding saturation need to be optimized by the Genetic Algorithm based on the initial relative permeability curves to match the experimental results. The outcomes show that the optimized absolute permeability is 19.63% higher than the experimentally measured value, and the optimized residual water saturation is 17.46% lower than the experimental residual water saturation. For the other saturations, the differences between the optimized relative permeability and the experimental results range from 25.93% to 10.57%. The whole divergence of the experiment results and the simulation results about average water saturation and inlet pressure using optimized Kr curves is 1.57%, far less than 69.72% of the unoptimized Kr curves. This research is of great significance for accurately obtaining the relative permeability curves of the tight oil reservoir with intense capillary pressure. • A modified black-oil model is built for accurately simulating capillary end effect. • Lower water injection rate affects relative permeability curves more significantly. • The actual residual water saturation is 17.46% lower than the measured one.