Empirical correlations for prediction of minimum miscible pressure and near-miscible pressure interval for oil and CO2 systems

Abstract

Although near-miscible CO2 flooding has recently received considerable attention, no criteria are available to predict its applicability to a specific reservoir. Evaluating the viability of near-miscible flooding requires experimental exploration of a specific region in pressure–temperature space. The near-miscible pressure field is bounded on one side in P, T space by the MMP (minimum miscible pressure). This paper provides robust empirical correlations to estimate the MMP for both pure and impure CO2 and for prediction of the near-miscible pressure region for CO2-oil. Many slim tube analyses, lacking high density data points, systematically underestimate the MMP, when the near miscible region is not accounted for. They are based on 147 published data sets that include: slim tube experimental determination of MMP; interfacial tension (IFT) between oil and CO2; concentration of solution gas; and purity of the CO2. This paper is the first to begin a systematic exploration of the pressure-temperature space within which near-miscible effects characterize CO2 floods. Our new correlations provide a basis for identifying and investigating the nature of near miscible effects associated with existing CO2 floods. For a case study of an offshore field we determined that lower and upper pressure boundaries for effective near-miscible flooding, are 0.87 MMP and 1.07 MMP at reservoir temperatures. The proposed model is the first empirical correlation for the prediction of near-miscible pressure region, it will provide the basis for both screening the relative potential of oil reservoirs for economically viable miscible or near-miscible CO2-flooding.