Aspects of petroleum basin evolution due to gas advection and evaporative fractionation

Dividing a suite of 535 PVT analyses (detailed analyses plus 340 analyzed to P7+) of world wide provenance into seven subsets on the basis of C1/C2 ratios, a well defined, separate regression of gas/oil ratio on saturation pressure is revealed in each subset. Such correlations depend primarily upon the processes involved in evaporative fractionation. The curves embrace the full, commonly encountered, range of combinations of gas/oil ratio and saturation pressure, both of which correlate poorly with level of maturity expressed in a liquid fraction slope factor. These observations lead to the hypothesis that progressive evaporative fractionation is a widespread, if not universal, evolutionary process in petroleum basins.