中国含油气盆地中的超压体系

随着石油勘探程度的提高及钻探深度的加深，我国含油气盆地中超压体系陆续地被揭露出来。目前已发现29个地区具有超压，而且发现它们与油气有密切的关系。一般超压体系就是烃源岩，但也可以作为盖层，对下伏油气藏起压力封闭作用。超压又是油气运移的原动力，它迫使地下流体通过水力压裂断层或各种输导层，由高势区向低势区运移、聚集。强超压储层(压力系数>2)成藏比较困难，从理论上讲除非周围泥岩(烃原岩)压力系数比储层还大，也可成藏。经考察在一些特定的地质条件下强超压储层也可以成藏，所以在具有超压体系的含油气盆地中，首先应搞清超压体系的成因分布规律，特别注重那些压力、温度正异常区，因为无论是在平面上，还是在纵向上这些异常区，都是压力突破点，代表地下流体主泄露区，是油气最有利的聚集区，应作为勘探的靶区。

OVERPRESSURE SYSTEM OF HYDROCARBON-BEARING BASINS IN CHINA

With the deepening of petroleum exploration and drilling, the overpressures are revealed in China's hydrocarbon-bearing basins and so far 29 overpressure provinces are found. The provinces have close ties with the petroleum concept. The overpres- sure systems are generally source rocks and sometimes also caprocks acting as pressure confining bed for the underlying petroleum and gas accumulation. The overpressure, which is the motive power for hydrocarbon migration, compels the fluids pass through various fractured faults or transporting strata and migrates from high potential zone to low potential zone and then accumulate. The hard overpressure reservoir(pressure coefficient>2)is difficult to form, except the pressure coefficient in the adjoining mudstone(source rock)is bigger than that in the reservoir. Under some special conditions, the hard overpressure reser voir may also form. Therefore the first thing is to get a clear understanding about the origin and distribution of overpressures, especially the zones with abnormal pressure and temperature. Because both horizontally and vertically these abnormal zones are the main leak zones for subsurface fluid and favorable accumulation zones of hydrocarbon, as well as the target zones for drilling.