Residual Trapping of CO2 in an Oil-Filled, Oil-Wet Sandstone Core: Results of Three-Phase Pore-Scale Imaging

CO2 geosequestration in oil reservoirs is an economically attractive solution as it can be combined with enhanced oil recovery (CO2-EOR). However, the effectiveness of the associated three-phase displacement processes has not been tested at the micrometer pore scale, which determines the overall reservoir-scale fluid dynamics and thus CO2-EOR project success. We thus imaged such displacement processes in situ in 3-D with X-ray microcomputed tomography at high resolution at reservoir conditions and found that oil extraction was enhanced substantially, while a significant residual CO2 saturation (13.5%) could be achieved in oil-wet rock. Statistics of the residual CO2 and oil clusters are also provided; they are similar to what is found in analogue two-phase systems although some details are different, and displacement processes are significantly more complex.