Experimental studies on CO2-brine-decane relative permeabilities in Berea sandstone with new steady-state and unsteady-state methods
CO2 relative permeability is the key parameter in modeling CO2 geological storage and CO2 enhanced oil recovery. However, the literature CO2 relative permeability data are often inconsistent and smaller than the actual values. This is because the traditional methods only obtain the global values of the three key parameters in relative permeability determinations: pressure drop, saturation and phase flux. These global values are often different from the local values due to capillary effects. This work develops new steady-state and unsteady-state methods to determine relative permeabilities. The new methods obtain the local values of the three key parameters, hence they have the advantage of experimentally avoiding capillary effects, which is crucial for gas and supercritical phase, such as CO2. The new methods give more accurate relative permeability data that are up to 50% higher than the traditional methods. This work uses the new methods to determine two-phase relative permeabilities for CO2-brine in Berea sandstone at different conditions (20-60 °C and 8-12 MPa). Within the scatter of data obtained here, the two-phase CO2 relative permeability data at different temperature and pressure conditions are similar. To ultimately resolve whether two-phase CO2 relative permeability depends on temperature and pressure, experimental relative permeability data with less scatter are needed in future. This work also obtains three-phase CO2 and decane relative permeabilities at 70 °C and 8 MPa when water is immobile. The key findings are: (1) the three-phase relative permeability of CO2 is higher than that of decane by one order of magnitude, which is consistent with CO2 being more non-wetting than decane in water-wet rocks; and (2) the three-phase CO2 relative permeability is lower than the two-phase CO2 relative permeability by another order of magnitude, which is consistent with CO2 becoming less non-wetting and getting similar to decane at high pressure. Thus when modeling water-oil-CO2 three-phase flows, the CO2 relative permeability curve can vary significantly with temperature and pressure since thermodynamics affects wettability and interfacial tension.