库车山前逆冲带超压流体主排放通道对油气成藏的控制

前陆逆冲带通常具有异常高压、构造圈闭发育和成藏条件复杂的特点,是油气勘探的高风险地区。对库车坳陷克拉苏逆冲带钻井、地质、地球化学资料的研究证实,克拉2特大型气藏形成于超压流体主排放通道上。该区构造挤压强烈,逆冲断裂活动伴随着下第三系膏泥岩/盐岩塑性流动,那些与膏泥岩/盐岩封闭层变薄、形成局部薄弱带相关的断层成为超压流体排放的主要通道。超压流体主排放通道是该区天然气垂向运移的主要途径,使得下部烃源岩层系中的天然气不断地向上部白垩系它源储层运移。超压流体排放有助于形成溶蚀孔隙,改善储层物性。综合研究表明,超压流体主排放通道对该区天然气成藏具有控制作用。

Control of main expelling pathway for overpressure fluid on gas migration and accumulation in Kelasu Thrust Belt of Kuche Depression

Huge natural gas resources have been proved in the Kelasu Thrust Belt of Kuche Depression. In spite of many structural traps developed，this belt had encountered high risk of hydrocarbon exploration for tens of years. The investigation of geology，drilling and geochemistry shows that a huge gas reservoir was formed in the main expelling pathway for overpressure fluid system under the seal of Eogene gypcrete/salt due to compression stress. The overpressure fluid expulsion occurred preferentially along those thrust faults which cut across the sealed gypcrete/salt bed of the least thickness in the vicinity of belt. The overpressure fluid expelling leads to pressure reduced and then causes gas up-migration along the faults down through underlying Triassic-Jurassic source rocks. In general，the main expelling pathway of overpressure fluid controls gas accumulation in this area.