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.

摘 要东营凹陷异常压力的分带性与泥岩的突破压力（或保存能力）具有明显的对应关系，随着深度增加，泥岩突破压力及地层流体压力系数均增大，泥岩封隔层对流体压力的保存也是形成异常压力的重要条件。基于增压机制的阶段性差异，对东营凹陷平面上及典型剖面中重要地质历史时期源动力（烃源岩流体压力）场进行了分析，主力烃源岩的源动力在时间和空间上发育不均衡，从整体上影响了储集层油气来源及油藏的形成，控制了油气运移的方向。现今油藏总体沿地质历史时期源动力场降低的方向分布，表现出油藏的分布与源动力的演化具有一定的继承性；油气运移和成藏也影响了地层压力场的分布，高压油气运移到储集层后，其泥岩封隔层不同程度地保存了流体压力。由于增压-卸压的平衡关系，源动力传递过程中在不同压力系统中构成了不同的动力条件，造成了各压力系统中油气成藏类型和特征具有一定的差异性。根据源动力的演化史，指出沙河街组深层是寻找高压轻质油藏及天然气藏的重要目标。