In Situ Analysis of Flow and Morphology Properties at the Pore Scale During CO2-Enhanced Oil Recovery

Abstract

Carbon dioxide-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 deg and 140 deg 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.