A Laboratory Investigation of Enhanced Gas Recovery by CO2 Injection

A coreflood study was undertaken to measure dynamic displacement characteristics of CO2, CH4, and brine as part of a feasibility study for a proposed carbon capture, utilization, and storage (CCUS) development. The planned project involves the separation of CO2 from reservoir gas and its reinjection into the reservoir. This was both to sequestrate the CO2 and to recover trapped hydrocarbon gas from the underlying paleo-residual gas (PRG) zone. Key parameters measured in order to model the enhanced gas recovery (EGR) process included drainage and imbibition relative permeabilities, trapped gas saturations, and hydrocarbon gas recovery efficiency. To properly reproduce the miscibility conditions for the EGR process, equilibrium fluids at reservoir conditions were used. Reservoir conditions were also applied, as the wetting behavior of CO2—being in the supercritical state under the test conditions—was uncertain based on the literature. Strong water-wet conditions would favor water blocking of the trapped methane to the injected CO2, whereas partial CO2 wetting, as some literature suggests, would imply less water blocking. In addition to the characterization of the EGR efficiency, trapped methane and trapped CO2 were measured during the special core analysis (SCAL) program. Differences in Land correlations for these fluids were observed for a given rock type. Trapped CO2 was found to be 15% lower than trapped CH4 at the same reservoir conditions. The trapped gas saturation to methane and CO2 was modeled by digital rock physics, and this implied the CO2 was partially wetting.