地层抬升引发的天然气膨胀及其聚集效应——以鄂尔多斯盆地苏里格气田为例

Gas expansion caused by formation uplifting and its effects on tight gas accumulation:A case study of Sulige gas field in Ordos Basin,SW China

应用大量地球化学、流体包裹体和生产动态等资料,对鄂尔多斯盆地苏里格气田晚白垩世以来大幅度抬升引发的天然气膨胀及其聚集效应进行研究。结果表明,晚白垩世以来,盆地显著抬升引发的天然气膨胀作用是苏里格气田致密砂岩气后期调整和二次充注的重要动力。抬升引起烃源岩中滞留的天然气体积膨胀导致天然气再次排出并运移充注到储集层,从而形成二次聚集效应,致密储集层中天然气的膨胀则引起含气饱和度、含气面积及气柱高度增加,进一步提高了储集层含气性,形成规模天然气聚集调整事件。整体上,苏里格气田经历早白垩世末前埋藏和晚白垩世以来抬升两期天然气聚集过程,埋藏阶段天然气主要受生烃超压驱动运移并聚集,抬升阶段则为天然气体积膨胀产生的膨胀力驱动的储集层内部调整和二次充注聚集。总体上,气田东部抬升阶段的天然气调整及二次充注聚集效应大于西部,有利于形成富气区。

Gas expansion caused by significant formation uplifting in the Sulige gas field in the Ordos Basin since Late Cretaceous and its effects on hydrocarbon accumulation have been investigated systematically based on comprehensive analysis of geochemical,fluid inclusion and production data.The results indicate that gas volume expansion since the Late Cretaceous was the driving force for adjustment and secondary charging of tight sandstone gas reservoirs in the Sulige gas field of the Ordos Basin.The gas retained in the source rocks expanded in volume,resulting in gas re-expulsion,migration and secondary charging into reservoirs,while the gas volume expansion in the tight reservoirs caused the increase of gas saturation,gas-bearing area and gas column height,which worked together to increase the gas content of the reservoir and bring about large-scale gas accumulation events.The Sulige gas field had experienced a two-stage formation process,burial before the end of Early Cretaceous and uplifting since the Late Cretaceous.In the burial stage,natural gas was driven by hydrocarbon generation overpressure to migrate and accumulate,while in the uplifting stage,the gas volume expansion drove internal adjustment inside gas reservoirs and secondary charging to form new reservoirs.On the whole,the gas reservoir adjustment and secondary charging during uplifting stage is more significant in the eastern gas field than that in the west,which is favorable for forming gas-rich area.