PRESSURE SOLUTION IN CARBONATE SOURCE ROCKS AND ITS CONTROL ON PETROLEUM GENERATION AND MIGRATION

Based on detailed geochemical and petrographic studies of conventional cores of a Triassic age carbonate source rock formation from three we ll sites at increasing maturity stages, it is shown that the effects o f carbonate diagenesis, especially pressure solution during relatively shallow burial stages, exercise major controls on the processes of pe troleum generation and migration during deeper burial. Pressure soluti on leads to an internal redistribution of organic matter within this s ource rock formation in the form of local concentrations as solution s eams and stylolites. They provide very favourable conditions for effec tive petroleum generation and migration due to their internal structur e and composition (three-dimensional arrangement of kerogen surrounded by carbonate-cemented rims as tight seals). The geochemical and petro graphic effects of petroleum generation and expulsion are documented, e.g. the expulsion of petroleum occurred as a separate phase fluid, at high efficiencies (60-80% for the normal and isoprenoid alkanes) and was facilitated by fractures presumably resulting from pore fluid over pressuring. A five-stage conceptual model is proposed to explain how t he effects of pressure solution achieved during relatively shallow bur ial stages exercised controls on the extent and efficiency of petroleu m generation and expulsion during deeper burial stages.