Consecutive Experimental Determination of Stress-Dependent Fluid Flow Properties of Berea Sandstone and Implications for Two-Phase Flow Modeling

In this study, changes in the hydrodynamic properties of Berea sandstone at a constant temperature of 40 degrees C are reported as effective confining stress is increased to 30 MPa. Through a novel consecutive approach, porosity, absolute permeability, drainage relative permeability, and drainage capillary pressure were shown to systematically change with effective stress. The relative permeability measurements were taken using a steady-state method for the N-2/water fluid pair. A second method, in which a saturated core with the wetting phase was flushed with the non-wetting phase at an increasing flow rate, was used to determine the drainage capillary pressure. Core saturation was determined using a gas separation unit and mass-balance considerations. This study revealed a decrease in porosity and absolute permeability, from 13.16% and 58 mD to 12.24% and 36 mD, respectively, with the increase in effective confining stress. In terms of relative permeability curves, this study showed a systematic decrease in irreducible wetting phase saturation from 0.44 to 0.24 as effective stress increased; this could be interpreted in core-scale as a progressive tendency of the initially water-wet Berea sandstone to the gas phase. The capillary pressure curve also presented an upward shift in response to increased effective stress. These changes in the hydrodynamic rock properties with stress suggest that scaling flow parameters of porous media under effective stress conditions may be required to accurately predict flow behavior under conditions of changing stress.