Effective Algorithm for Calculation of Minimum Miscibility Pressure

This paper describes a new algorithm developed for calculation of the minimum miscibility pressure (MMP) for the displacement of oil by a multicomponent injection gas. The algorithm is based on the key tie line identification approach initially studied by Wang and Orr . A new global formulation is introduced to describe and locate the sequence of nc- 1 key tie lines controlling the development of miscibility. In this new formulation, a number of numerical weaknesses of the original approach have been eliminated resulting in a robust and highly efficient algorithm. The computation time is reduced significantly and is clearly superior to other methods described in the literature. For a 15 component fluid description the MMP is determined within a few seconds on a PC. Hence the algorithm offers an efficient tool for projects where a large number of MMP calculations are needed (e.g. lumping and gas enrichment studies).

A case study is presented based on a real reservoir fluid for which PVT studies, swelling test and slimtube experiments have been performed. The study aims at investigating the influence of the characterization, tuning and lumping procedure used for generating a fluid description on the prediction of the MMP.

Based on the generated fluid description, a gas enrichment study is presented where the optimum mixture of two available injection gasses is determined aiming to optimize the gas injection project.