A comprehensive analysis of factors influencing CO2-oil displacement in sandstones under reservoir conditions by online nuclear magnetic resonance testing

Carbon Capture, Utilization and Storage-Enhanced Oil Recovery (CCUS-EOR) technology can effectively improve crude oil recovery while simultaneously sequestering CO 2 in geological formations to reduce emissions. The distribution and migration patterns of oil and gas in reservoir rock masses remain one of the key issues worthy of study, among which CO 2 -oil displacement experiments are the most direct research method. Nuclear Magnetic Resonance (NMR) provides technical assurance for the visualization and quantification of displacement experiments. Different from previous studies, we selected experimental cores based on their pore characteristics and optimized the experimental scheme. Strictly controlled single variables were used to determine the effects of various factors, including injection pressure, temperature, pore structure, permeability, and crude oil viscosity, on CO₂ flooding efficiency. An in-depth analysis of the oil and gas migration mechanisms during CO 2 flooding was conducted using T 2 relaxation spectra and oil-filled porosity distribution maps. The study identified oil recovery has nonlinear relationship with injection pressure and near-linear relationships with temperature, compared the displacement differences between medium and high viscosity oils, and revealed the dominant role of pore structure on oil recovery effectiveness. It is worth noting that the order-of-magnitude change in permeability did not significantly improve oil recovery, which is quite different from previous studies.