超压盆地油气垂向运移高度研究

在超压盆地中,当断层活动断开超压烃源岩时,油气会沿断层面发生涌流式垂向运移,这一瞬态涌流过程为油气大规模运聚成藏提供了重要的油气来源。然而,对于油气沿断层垂向运移距离问题的研究,停留在定性分析阶段,较少考虑到断层开启时造成的泄压作用,也很少区分地层水和油气运移距离的差异。本文认为,油气顺断层向上运移的距离主要由源岩超压带内超压幅度决定,油气垂向运移理论高度可由超压幅度折算,因而超压幅度越大,油气垂向运移距离越远,油气上涌顶界面埋深越浅。油气初次上涌的起始位置不是地表面,而是有效烃源岩顶面。另外,由于油气的大量上涌,超压带快速泄压,大部分油气上涌实际距离不能达到理论上涌的最大距离。同时,考虑到沿断层运移时受到阻力作用,油气实际上垂向运移高度远远小于理论运移高度。

Study on Vertical Migration Height of Hydrocarbon in Overpressure Basin

Hydrocarbon of overpressure basins can vertically migrate along faults through inrush current when active fault cut through the overpressure source rocks.This process provides an important hydrocarbon source for large scale migration and accumulation. However, the research on the distance of hydrocarbon vertical migration is still in qualitative analysis stage, with less attention on pressure relief during fault opening and migration distance difference between hydrocarbon and the formation water. This paper shows that the height of hydrocarbon vertical migration along fault relies on the overpressure amplitude in source rocks. The larger the amplitude is, the farther the hydrocarbon can migrate vertically. Consequently, the top interface of upwelling is buried more shallowly.The initial position of hydrocarbon upwelling is not ground surface but the top of effective source rock. With vertical inrushing of a large volume of hydrocarbon, the pressure in overpressure belt releases rapidly so that great majority of hydrocarbon cannot reach the theoretical top interface of upwelling. Besides, taking the resistance of vertical migration along faults into account, the real height of vertical migration of hydrocarbon will be far lower than the theoretical migration distance.