Nanoscale-extended correlation to calculate gas solvent minimum miscibility pressures in tight oil reservoirs

Abstract

In this paper, a novel nanoscale-extended correlation is developed to calculate the minimum miscibility pressures (MMPs) for a wide range of dead and live tight oil−gas solvent systems in bulk phase and nanopores. First, experimentally, the slim-tube and coreflood tests as well as the vanishing interfacial tension (VIT) technique are conducted to measure the MMPs of three oil‒gas systems. Second, the newly-developed correlation is proposed as a function of the reservoir temperature, molecular weight of C5+, mole fraction ratios of volatile components to intermediate components in oil and gas samples, and pore radius. Third, theoretically, the new correlation is analyzed on a basis of an oil‒gas MMP database from this study and literature that covers 101 oil‒gas MMP data for fifteen oil and thirteen gas samples at different reservoir temperatures in bulk phase and nanopores. A total of 40 commonly-used existing correlations are analyzed and reviewed. Compared to the seven existing correlations, the new correlation is found to provide the most accurate MMPs with an overall percentage average absolute deviation (AAD%) of 5.72% and maximum absolute deviation (MAD%) of 12.96% for different dead and live oil‒pure CO2 systems in bulk phase. Moreover, for the different oil‒pure and impure gas solvent systems, the new correlation leads to the best calculation accuracy of the MMPs with an overall AAD% of 4.70% and MAD% of 15.81% in comparison with the four existing correlations. More importantly, the new correlation is found to calculate the MMPs of different dead and live oil‒pure and impure gas solvent systems in nanopores in an accurate, efficient, and physical correct manner. The overall AAD% and MAD% in terms of the MMP calculations in nanopores from the new correlation are determined to be 6.91% and 13.66%, respectively.