Minimum miscibility pressure estimation for a CO₂/n-decane system in porous media by X-ray CT

Accurate determination of gas–fluid miscibility conditions is important to optimize the displacement efficiency during CO₂-enhanced oil recovery. This paper presents a new technique to investigate the phase behavior and to estimate the minimum miscibility pressure (MMP) of a CO₂/n-decane system using an X-ray computerized tomography (CT) scanner. CT scans of the CO₂/n-decane system are taken at various pressures during the experiments. The image intensity values taken from the CT images have a linear relationship with the densities of the measured objects; therefore, we can estimate the miscible point of CO₂ and n-decane because the difference between the intensity values for each phase decays to zero as the pressure increases toward the MMP. This paper provides experimental evidence for the validity of the new CT method by comparing the results with previous studies and presents an application of the method to investigate the MMP of the CO₂/n-decane system in porous media. Additionally, the influence of porous media on the equilibrium state when the CO₂/n-decane system is close to miscibility is discussed.