Analytical Study of CO2 Minimum Miscibility Pressure Correlations and Their Accuracy for Nigerian Crude Oil Types in CO2 EOR Applications

Accurate determination of the minimum miscibility pressure for CO2 flooding is essential for designing effective carbon dioxide enhanced oil recovery programmes, and the applicability of published MMP correlations to Nigerian crude oil compositional characteristics has not been systematically validated. This study analytically evaluates the accuracy of nine published CO2 MMP correlations against experimentally measured MMP values for fifteen Nigerian crude oil types spanning a range of API gravity from 22 to 46 degrees. Slim tube experiments were conducted at reservoir temperatures for each crude oil, with MMP determined from the conventional 80 percent recovery efficiency criterion at the point of miscibility development. Correlation inputs including crude oil C5 plus fraction molecular weight, reservoir temperature, and C2 through C4 content of the injection gas stream were calculated from compositional analyses of each crude. Absolute average relative errors between measured and correlation-predicted MMPs were computed for each correlation across the Nigerian crude oil dataset. The Sebastian empirical correlation demonstrated the lowest mean absolute error of 7.3 percent, followed by the Metcalfe and Yarborough correlation at 9.8 percent mean error, while the widely used Yuan and Johns correlation significantly overpredicted MMP for high-API Nigerian crudes above 38 degrees gravity. A modified version of the Sebastian correlation with a Nigerian crude-specific regression adjustment is presented, reducing mean prediction error to 4.1 percent. Keywords: minimum miscibility pressure, CO2 EOR, Nigerian crude oil, slim tube experiment, correlation validation.