Improved MMP correlations for CO₂ floods using analytical gas flooding theory

Local displacement efficiency from CO₂ gas injection is highly dependent on the minimum miscibility pressure (MMP). Correlations are often 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 accurately account for the more complex condensing/vaporizing 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 (EOS) to generate MMP correlations for displacements by pure and impure CO₂.^1-8 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 slim-tube MMPs and other numerical methods. The improved MMP correlation is based solely on the reservoir temperature, molecular weight of C₇₊, and percentage of intermediates (C₂ - C₆) in the oil. The MMPs from the improved correlation are compared to currently used correlations and 41 experimentally measured MMPs. Correlations are also developed for impure CO₂ floods, where the injection stream may contain up to 40% methane. The new correlations are significantly more accurate and applicable than currently used correlations.