Wettability and capillary behavior in a CO2-oil-solid system under near-miscible conditions: A pore-scale study

Carbon dioxide -enhanced oil recovery (CO2-EOR) is an important means of improving oil recovery while lowering greenhouse gas emissions. However, it is still challenging to determine the pore -scale flow characteristics and interfacial interaction parameters, such as the wettability, interfacial curvature, and capillary pressure, under near -miscible conditions. In this study, X-ray microtomography (micro -CT) was used to determine the morphology of gas and oil phases and characterize the in -situ wettability under near -miscible conditions. The mean contact angle increased from 66.99 degrees to 72.5 degrees as the injected CO2 pore volume (PV) increased from 5.5 PV to 33.1 PV. The wettability was locally altered as the local contact angle changed from 44.14 degrees to 107.27 degrees because of preferential adsorption of CO2 molecules over oil molecules on solid surfaces. The mixed -wet condition was reflected by local contact angles both below and above 90 degrees, and the capillary pressure exhibited a tower -shaped distribution with a peak value around zero, which promoted oil recovery. At the end of the displacement process, the interfaces were pushed toward the corners by a reduction in the capillary pressure, resulting in interface recession and a reduction in CO2 clusters. Pore occupancy studies showed that under near -miscible conditions, gas usually occupies large pores and oil resides in pores of varying sizes, which can result in optimal recovery.