沉积盆地超压系统演化与深层油气成藏条件

晚期成藏是大中型油气田形成的重要特征。从晚期成藏的观点出发，深层油气藏的形成需要盆地深层发育仍处于有利生，排烃阶段的源岩，具有较高孔隙度，渗透率的深部储层，以及有利的储层－盖层能量配置，在超压盆地中，超压对生烃的抑制作用使常压盆地中已过成熟的源岩保持在有利的生，排烃阶段，从而为深层油气成藏提供较好的烃源条件，超压条件下低有效应力引起的机械压实程度减弱，流体流动性减弱引起的化学胶结作用减缓及有机酸对矿物的溶解作用使深埋超压储层保持较高的孔隙度和渗透率。然而，由于超压引起的地层天然水力破裂和流体穿层运移。超压环境深部油气藏的形成和保存需要有效的储层－盖层能量配置。

Evolution of Overpressured Systems in Sedimentary Basins and Conditions for Deep Oil/Gas Accumulation

Accumulation at late stages has been confirmed to be an important characteristics of most large and medium sized oil/gas reservoirs in China. From the viewpoint of late accumulation, the existence of active source rocks and reservoir rocks with relatively high porosity and permeability in the deep part of the basin, and favorite pressure distribution between reservoir rocks and seals were required for the accumulation of deep oil/gas reservoirs. In overpressured basins, source rocks that would have reached the metagenetic stage without retardation in normally pressured basins have been kept within the zones favorable for hydrocarbon generation and expulsion due to overpressure retardation, which provides good hydrocarbon sources for oil/gas accumulations in the deep intervals. The weak mechanical compaction due to low effective stress, and weak chemical diagenesis due to closed or semi closed fluid systems in overpressured conditions lead to the preservation of relatively high porosities and permeabilities for the deeply buried sandstones. However, because of the natural hydraulic fracturing of strata and cross formation migration of fluids including oil and gas, effective energy distribution between reservoir rocks and seals are required for the accumulation and preservation of deep oil and gas accumulation in overpressured conditions.