Simplified method for calculation of minimum miscibility pressure or enrichment

Local displacement efficiency from gas injection is highly dependent on the minimum miscibility pressure (MMP) or minimum miscibility enrichment (MME). Analytical methods, which are inexpensive and quick to use, have been developed to estimate MMPs for complex fluid characterizations. Published methods, ^1-3 however, often require estimation of numerous parameters and little has been written with regard to method robustness. This paper presents a simplified and robust method for MMP or MME calculation. The approach relies on finding key crossover tie lines for a dispersion-free displacement using the method of characteristic theory (MOC). The new method, however, differs from published methods by significantly reducing the number of equations and unknown parameters, and by providing a fast and robust method that can avoid trivial and false solutions. We demonstrate the improvements by calculation of the MMP and MME for a variety of gas/oil systems and also give new analytical solutions for constant K-value systems that give insight into the nature of false solutions. The number of potential false solutions increases greatly with the number of components in the fluid characterization. Thus, any proposed method must ensure convergence to the physical MMP/MME.