Control of pressure system development on reservoir formation in the Dongying Sag, Shengli Oilfield, East China

The zonality of abnormal pressure is closely correspondent to the breakthrough pressure (or pressure preservative ability) of mudstones in the Dongying Sag. The breakthrough pressures and formation fluid pressure coefficients rise with increasing depth. The preservation of isolated mudstone intervals is also important to the abnormal pressure formation. Based on the episodic difference of pressure buildup mechanism, source dynamic (fluid pressure in source rocks) fields of critical geologic times were analyzed in lateral plane and vertical profiles in the Dongying Sag. Source dynamic of major source rocks occurs in disequilibrium with time and space, which affects oil-gas sources and reservoir formation and controls the direction of oil-gas migration as a whole. The present reservoirs are distributed along the pressure decreasing directions. The distribution of the reservoirs is successional to the evolution of source dynamic. On the other hand, oil-gas migration and accumulation affect the distribution of formation pressure fields. The isolated mudstone intervals preserve the fluid pressures to different extents. Due to the equilibrium between pressure buildup and pressure relief, source dynamic creates different conditions in various pressure systems during its transference, which cause the differences in types and features of oil-gas reservoirs. Based on the evolutionary history of source dynamic, the reservoir forming process in the Dongying Sag was analyzed. The deep layers of the Shahejie Formation are important targets for us to discover light hydrocarbon and natural gas reservoirs with high pressures.