Experimental investigation of the formation and distribution of remaining oil from pore scale to core scale during supercritical CO2 flooding

Research on the formation and distribution characteristics of remaining oil has primarily focused on individual scales, with studies at both the pore scale and core scale often lacking effective integration, particularly under supercritical conditions. In this study, a high-temperature and high-pressure microfluidic experimental system (temperature: 75 °C, pressure: 22 MPa) and micro-computed tomography (CT) scanning technology were employed to systematically investigate the formation mechanisms and distribution characteristics of five different types of remaining oil after CO2 injection. The experimental results indicate that after CO2 injection, the remaining oil mainly appears in columnar and droplet patterns, predominantly distributed in pores ranging from 4 to 13 μm, and is significantly influenced by the Marangoni effect and Jamin effect. Additionally, at the pore scale, the oil recovery increased by approximately 8.7% under high flow rates (0.5 ml/min) compared to low flow rates (0.1 ml/min); In contrast, at the core scale, the oil recovery decreased by 15.9%. This contrasting behavior can be attributed to flow non-uniformity caused by the fingering effect, which leads to uneven fluid distribution within the porous media. The comparison between pore scale and core scale provides new insights into understanding the distribution patterns of remaining oil.