CO2 injection to underground formations can reduce CO2 emissions, enhance hydrocarbon and methane recovery, and extract geothermal heat. As the pressure and temperature in the geological formations vary with reservoirs, the injected CO2 can be in gas, liquid and supercritical phase. Research work on CO2 storage has mainly focused on trapping mechanism, risk assessment, storage site selection, etc., but detailed experimental studies on the impact of CO2 phases on its injection and displacement in different geological formations has largely been neglected. In this paper, experimental work was designed to investigate the effect of CO2 phase on its injection and displacement in a 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 liquid CO2 displacements, particularly before CO2 breakthrough. Gas and supercritical CO2 injection gave a water production rate much higher than the CO2 injection rate at early stages. Liquid CO2 injection gave a water production rate similar to the CO2 injection rate. The highest water recovery was obtained after the injection of 0.85, 1.08 and 2.32 pore volume of scCO2, gCO2, and LCO2, respectively. This may indicate that the injection of supercritical CO2 or gas CO2 (under a pressure higher than 60 bars) could give a high and quick oil production. The residual water saturations for the three CO2 phases were in the range of 30 to 33% while the relative permeability was in the range of 0.18-0.21. The end-point 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 end-point relative permeabilities for the three CO2 phases.
- CO2 phase
- enhance hydrocarbon and methane recovery
- CO2 injection