Pore-scale observations of supercritical CO2 drainage in Bentheimer sandstone by synchrotron x-ray imaging

This work utilizes synchrotron-based x-ray computed microtomography (x-ray CMT) imaging to quantify the volume and topology of supercritical carbon dioxide (scCO2) on a pore-scale basis throughout the primary drainage process of a 6 mm diameter Bentheimer sandstone core. Experiments were performed with brine and scCO2 at 8.3 MPa (1200 psi) and 37.5 °C. Capillary pressure-saturation curves for the scCO2-brine system are presented and compared to the ambient air-brine system, and are shown to overlay one another when pressure is normalized by interfacial tension. Results are analyzed from images with a voxel resolution of 4.65 μm; image-based evidence demonstrates that scCO2 invades the pore space in a capillary fingering regime at a mobility ratio M = 0.03 and capillary number Ca = 10−8.6 to an end-of-drainage brine saturation of 9%. We provide evidence of the applicability of previous two-dimensional micromodel studies and ambient condition experiments in predicting flow regimes occurring during scCO2 injection.