A Thermodynamic Correlation for the Minimum Miscibility Pressure in CO2 Flooding of Petroleum Reservoirs

Summary A graphic equation-of-state (EOS)-generated correlation for the minimum miscibility pressure (MMP) of CO2/crude-oil displacements is presented, along with a brief review of 17 other MMP correlations. The MMP is estimated as the cricondenbar or first-contact miscibility pressure of the pure or impure CO2/crude-oil system in which the C5+ oil fraction is modeled as a single normal alkane of equivalent molecular weight. The correlation accounts for all the experimentally observed trends in MMP in a consistent manner and is independent of any CO2/crude-oil data base. A correction is introduced, however, to prevent a predicted increase in the MMP with decreasing temperature at low temperatures for high-molecular-weight oils. The average predicted-MMP/experimental-MMP ratio for 157 CO2/crude-oil MMP values is 1.09, with a standard deviation of 0.19. Unlike other correlations, specifically those relating MMP with CO2 density, a decrease in MMP with temperature at elevated temperatures (> 120°C [> 248°F]) is predicted.