Thermodynamic modeling of petroleum inclusions: Composition modeling and prediction of the trapping pressure of crude oils

Microthermometry and volumetric analysis have been widely used to reconstruct the composition and P–T trapping conditions of petroleum inclusions. However, a reliable prediction of the P–T trapping conditions requires efficient thermodynamic modeling of the PVT properties to obtain the saturation pressure and petroleum volume prediction in addition to accurate measurements of the homogenization temperature, Th, and the degree of bubble filling, Fv. Until now, no critical appraisal of the volume prediction has been performed. Using an extensive compilation of data from the literature (909 points for the volume), we demonstrate that it is possible to have good predictions on the saturation pressures and volume characteristics of crude oils. Our improved Fv is correlated with the molar fraction of C7+ cut and the Th value of the oil inclusion. We develop a new composition modeling method based on the α–β composition model by tuning the C7+ molar fraction. However, the ability of the new method to predict the trapping pressure is still strongly dependent on the accuracy of the saturation pressure estimation and the modeled Fv. A large number of reservoir fluids (N = 160) has therefore been used to derive the correlations between the trapping pressure prediction and the composition and saturation pressure. The formulation only relate to the molar fraction of methane. The new correlations are of interest as they reduce the number of relevant variables, in particular eliminating the effect of Fv on the trapping pressure prediction. Finally, we tested the accuracy of the new method in predicting the trapping pressure, emphasizing the influence of the bulk methane mole fraction on the trapping pressure. There is a need for future research on the prediction of the methane mole fraction in petroleum inclusions.