超压与烃类生成相互作用关系及对油气运聚成藏的影响

Study on the interaction of overpressure and hydrocarbon generation and the influence of overpressure upon hydrocarbon accumulations

世界含油气盆地中超压分布广泛且对油气勘探开发影响深远。超压的成因可概括为 3种 :地层不均衡压实、构造挤压、与流体作用 (烃类生成、水热膨胀、黏土矿物脱水等 )有关。油气 (尤其是天然气 )的大量生成及排烃不畅导致超压的形成 ;超压的存在又使油气生成速率降低 ,液态窗的下限下移。超压对储集层的控制作用在于减缓压实 ,使深层储集物性得到改善 ;另外 ,超压改变了岩石破裂时的应力条件 ,导致深层泥岩裂缝储集层发育。超压是油气运移的动力 ,对油气运聚成藏起着控制作用 ,若圈闭中超压的形成早于油气的充注 ,对油气成藏不利 ;若圈闭中超压的形成恰是油气充注的结果 ,则有利于油气成藏。一般而言 ,油气多聚集在超压体的过渡带中。图 4参 2 9(王兆云摘 )

Overpressures are widespread throughout the global oil and gas basin and have great influence to exploration. A variety of processes have been proposed for the generation of overpressure, it can be summarized into three types, compaction disequilibrium, tectonic compression and fluid affection. In the latter case, fluid process includes hydrocarbon generation, aquathermal expansion, clay mineral dehydration etc. It is indicated that overpressure and evolution of source rock is interactional and inter restricted. On one side, the large generation of hydrocarbon, specially the large generation and migration of gas or the block of migration resulted in overpressure; on the other side, overpressure restrained thermal evolution of source rock due to the decrease of hydrocarbon generation rate and made oil window deeper. Overpressures reduced the compaction and improved the reservoir quality. In addition, overpressure changed the in situ stress conditions under which the rock broke, and resulted in the development of fractured shale reservoirs. Overpressure is the motive power of hydrocarbon migration and controls the hydrocarbon accumulation. If the formation of overpressure in the trap is earlier than the charge of hydrocarbon, it is not good for the hydrocarbon accumulation; otherwise, it is very benefit for hydrocarbon accumulation if the formation of overpressure is the result of the hydrocarbon charge. Commonly, the hydrocarbon accumulated mainly in the transition zone of overpressure body.