文摘
In geologic carbon sequestration, capillary pressure (Pc)鈥搒aturation (Sw) relations are needed to predict reservoir processes. Capillarity and its hysteresis have been extensively studied in oil鈥搘ater and gas鈥搘ater systems, but few measurements have been reported for supercritical (sc) CO2鈥搘ater. Here, Pc鈥?i>Sw relations of scCO2 displacing brine (drainage), and brine rewetting (imbibition) were studied to understand CO2 transport and trapping behavior under reservoir conditions. Hysteretic drainage and imbibition Pc鈥?i>Sw curves were measured in limestone sands at 45 掳C under elevated pressures (8.5 and 12.0 MPa) for scCO2鈥揵rine, and in limestone and dolomite sands at 23 掳C (0.1 MPa) for air鈥揵rine using a new computer programmed porous plate apparatus. scCO2鈥揵rine drainage and imbibition curves shifted to lower Pc relative to predictions based on interfacial tension, and therefore deviated from capillary scaling predictions for hydrophilic interactions. Fitting universal scaled drainage and imbibition curves show that wettability alteration resulted from scCO2 exposure over the course of months-long experiments. Residual trapping of the nonwetting phases was determined at Pc = 0 during imbibition. Amounts of trapped scCO2 were significantly larger than for those for air, and increased with pressure (depth), initial scCO2 saturation, and time. These results have important implications for scCO2 distribution, trapping, and leakage potential.