沉积盆地超压形成机制述评

超压形成机制可以归纳为三大类:(1)岩石压力的增加;(2)孔隙流体或岩石骨架体积的变化;(3)流体流动及烃类上浮.低渗透性的沉积物在快速沉降过程中,上覆岩层产生的不均衡压实可产生相当大的超压,这是沉积盆地形成高压的主要机制.构造活动的地区,水平应力变化可以快速产生并迅速释放大量的超压.除非有非常理想的封闭性,否则由水热膨胀和粘土脱水引起的流体体积增加不足以形成超压.烃类生成和裂解成气具有形成超压的潜能,但压力需要较长时间才能得以聚集,所以,这一机理也值得怀疑.

A COMMENT ON FORMINGMECHANISM OF OVERPRESSURE IN SEDIMENTARY BASINS

The formation mechanism of overpressure can be divided into following three types:1.the increase of compressive stress;2.changes in the volume of pore fluid or rock matrix,and 3.hydrocarbon buoyancy or liquid flowage.Loading during burial can produce considerable overpressure due to disequilibrium compaction,particularly during the rapid subsidence of low-permeability sediments.Horizontal stress changes can rapidly produce or release large amounts of overpressure in tectonically active areas.The increases fluid volume caused by aquathermal expansion and clay dehydration are too small to produce significant overpressure unless perfect sealing occurs.Hydrocarbon generation and cracking could possibly produce overpressure,but it needs a long period of time for the pressure to cumulate.This requires to be further proved.