Improved MMP correlations for CO₂ floods using analytical gasflooding theory

Local displacement efficiency from CO₂ gas injection is highly dependent on the minimum miscibility pressure (MMP). Correlations are sometimes used to estimate the MMP where the injected fluid may or may not contain impurities such as methane. These correlations, however, are based on a limited set of experimental data and, as such, are not widely applicable. They also do not account accurately for the more complex condensing/vaporizing (CV) displacement process. This paper presents new MMP correlations for the displacement of multicomponent oil by CO₂ and impure CO₂. The approach is to use recently developed analytical theory for MMP calculations from equations of state (EOSs) to generate MMP correlations for displacements by pure and impure CO₂. The advantage of this approach is that MMPs for a wide range of temperatures and reservoir fluids can be calculated quickly and accurately without introducing uncertainties associated with slimtube MMPs and other numerical methods. The improved MMP correlations are based solely on the reservoir temperature, the molecular weight of C₇₊, and the percentage of intermediates (C₂-C₆) in the oil. The MMPs from the improved correlations are compared to currently used correlations and 41 experimentally measured MMPs. Correlations are also developed for impure-CO₂ floods, in which the injection stream may contain up to 40% methane. The new correlations are more accurate for a wider range of conditions than the currently used correlations.