Water/Oil Relative Permeability Endpoints of Intermediate-Wet, Low-Permeability Rocks

Summary The relative permeability endpoints of low-permeability, intermediate-wet mudstones increased with flow rate. This was because of both a decrease in capillary end effect and an increase in capillary number. Hence, conventional analysis will incorrectly describe field behavior. We recommend an improved methodology. We imaged steady-state saturation profiles at the end of different rate floods on one sample. We analyzed these profiles, which were axially nonuniform, to obtain capillary-end-effect-corrected data for each flow rate. The saturation distributions were also radially nonuniform. We characterized core-scale heterogeneity using a miscible flow test and examined the influence of heterogeneity. We conducted long-term tests on three short samples to study the higher-capillary-number regime. These tests displayed the existence of a critical capillary number, where the water relative permeability endpoint increased dramatically. The corresponding rate was over a magnitude smaller than flow rates traditionally recommended to eliminate capillary end effects.