Relative Permeability Correlation for Mixed-Wet Reservoirs

Abstract

Abstract A two-phase (oil-water) relative permeability correlation for mixed-wet reservoir rock is developed and validated in this paper, including bounding drainage and imbibition processes and scanning hysteresis loops, all integrated with the corresponding changes in capillary pressure. The Corey-Burdine type relative permeability correlation is widely used in the industry. It was originally developed for water-wet reservoirs from a Brooks-Corey power-law capillary pressure correlation in combination with a bundle-of-tubes model of the pore network. We have adjusted the Brooks-Corey capillary pressure correlation to be valid for mixed-wet rock and now present the ensuing Corey-Burdine relative permeability correlation for mixed-wet reservoirs. The functional form of the relative permeability correlation is symmetric with respect to fluid-dependent properties since neither fluid is privileged in a mixed-wet environment. It reverts to the standard Corey-Burdine correlation for the completely water- or oil-wet case. A water-wet behavior is displayed at low water saturations and an oil-wet behavior at low oil saturations, in accordance with experiments. The correlation provides an inverted S-shape oil relative permeability curve with an inflection point, and closed hysteresis scanning loops, as observed. The correlation is validated by comparison with measured relative permeability curves and simultaneously measured capillary pressure and relative permeability curves from the literature. The correlations and hysteresis logic are easily programmed, and we suggest that the Killough hysteresis model, employed in many numerical reservoir simulators, should be updated with the new scheme.