In-situ analysis of flow and morphology properties at the pore scale during CO₂-Enhanced Oil Recovery

Enhanced oil recovery(CO₂-EOR) is an essential technique to improve oil recovery while reducing greenhouse gas emissions. However, the pore-scale flow dynamics and morphological characteristics during the EOR process remain unclear. This study employs X-ray micro-tomography (micro-CT) to perform a displacement experiment through CO₂ flooding. The pore characteristics, in situ wettability, morphological parameters, and interfacial area are analyzed. The spatial distribution of pores and throats is discovered to be even, with both radii distributions exhibiting narrow peaks. The coordination number is predominantly located between 5 and 10, increasing with pore size. As the displacement process proceeds, the percentage of contact angle distribution between 105° and 140° increases, indicating the ability of CO₂ to remove the oil phase from the solid surface. As CO₂ is injected, the oil-solid interfacial area decreases while the CO₂-solid interfacial area increases, demonstrating the reduction in oil-wettability of the sample. The predominant form of residual gas at the end of displacement is residual film gas, characterized by positive Euler number values, indicating its existence as a disconnected phase. The isolated oil phase, characterized by a small volume and simple structure, dominates the remaining oil phase during CO₂ injection. The surface area and volume of the oil phase exhibit a power-law relationship with similar coefficients and exponents at various pore volumes (PVs). Some larger oil phases deviate from the fitted curve, possibly due to dissolution.