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

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.