In situ measurement of CO2-oil mixture phase behavior properties in porous media for CO2-enhanced oil recovery

Accurate characterization of the CO2-oil mixtures phase behavior will be advantageous for CO2 enhanced oil recovery (EOR) and reservoir production design for CO2 geologic storage projects. Relevant properties which include density, oil swelling factor, solubility and minimum miscibility pressure (MMP) of CO2-oil are typically measured in the laboratory using the conventional time-consuming pressure-volume-temperature (PVT) method. In this study, the phase behavior of CO2-oil mixtures was characterized inside a porous medium at reservoir temperature and pressure using nuclear magnetic resonance imaging (MRI). This research method realizes direct observation and in situ measurement compared with PVT method, effectively reducing the experimental operating pressure and the pressure-loading limit of the measurement equipment. The CO2-oil mixture equilibrium pressures correlated exponentially with the corresponding proton density (M0) and relaxation rates (1/T1, 1/T2); thus, the MRI multiparameter method was first applied to estimate MMP by only measuring several equilibrium pressure points and extrapolating to zero. The CO2 solubility and saturated liquid density linearly decreased as 1/ T1 increased but linearly increased as 1/T2 increased, which indicates that these parameters can be estimated based on the magnetic resonance (MR) relaxation rates. The results demonstrate the remarkable advantage and feasibility of applying MRI techniques for in situ measuring of the physical properties of fluids in porous media within the laboratory.