Effect of CO2 phase on its water displacements in a sandstone core sample

CO2 injection into underground formations can reduce CO2 emissions, enhance hydrocarbon and methane recovery, and extract geothermal heat. As the pressure and temperature vary in subsurface formations, the injected CO2 can be in gas, liquid and supercritical phase. The change in CO2 phase is likely to have a significant impact on capillary and viscous forces, which, in turn, will have a considerable influence on injectivity, displacement, migration, storage capacity and integrity of CO2 processes. This study was designed to investigate the effect of CO2 phase, at different injection rates, on the dynamic pressure evolution and the CO2 displacement performance during CO2 injection into a water-saturated sandstone core sample. The results indicate that CO2 phase significantly affects the differential pressure profile and water production profile. The differential pressure profiles measured from the displacement of supercritical CO2 and gas CO2 were significantly different from those measured from liquidCO2 displacements, particularly before CO2 breakthrough. Gas and supercriticalCO2 injection gave a water production rate much higher than the CO2 injection rate at early stages. Liquid CO2 injection yielded a water production rate similar to the CO2 injection rate. This may indicate that the injection of ScCO2or GCO2 (under a pressure higher than 60 bar) could give a high and quick oil production rate. The highest water recovery was obtained after the injection of 0.85, 1.08 and 2.32 pore volumes of scCO2, gCO2, and LCO2, respectively. The residual water saturations for the three CO2 phases were in the range of 30-33% while the endpoint relative permeability was in the range of 18-21%. The endpoint relative permeabilities for gas and liquid CO2 were very similar and higher than that of supercritical CO2 under our experimental conditions. The increase in injection rate caused a slight increase in the endpoint relative permeabilities for the three CO2 phases.