库车前陆盆地构造挤压作用下的天然气运聚效应探讨

以克拉2气田为例,探讨了喜马拉雅晚期强烈构造挤压作用下天然气的运聚效应。构造挤压引起流体压力的快速增加,打破前期相对稳定的流体势场;断裂带为相对低应力区,不增压或与周围岩层相比增压相对小,成为相对低势区,岩层中的天然气向断裂处汇聚,使断裂带势能增大;构造挤压使地层发生破裂和已有断裂开启,同时垂向上气势梯度也大幅度增大,深部天然气沿断裂的垂向运移动力得以增强,断裂带处汇聚天然气沿开启断裂向上部地层快速运移,并侧向充注区域性盖层下的砂体,最终在构造挤压作用下的相对低气势区聚集。喜马拉雅晚期以来库车前陆逆冲带盐下断背斜、背斜构造挤压作用下为相对低气势区,油源断裂发育,构造强烈活动使断裂开启,垂向上气势梯度大幅度增大,保存条件较好,为喜马拉雅晚期以来天然气有利聚集区。中西部前陆盆地构造挤压强烈,对天然气成藏具有重要影响。因此,开展前陆盆地构造挤压对天然气成藏的影响研究,对指导前陆盆地油气勘探具有重要的理论意义和应用。

Study on Impact of Tectonic Compression on Natural Gas Migration and Accumulation in Kuqa Foreland Basin

The paper analyzes the impacts of intensive tectonic compression on natural gas migration and accumulation in the later Himalayan period, taking the Kela 2 gas field in the Kuqa foreland basin as an example. Tectonic compression makes the fluid pressure rapidly increase and changes the previous relatively stable fluid potential field. The fault zone is a lower stress zone and becomes a lower potential area because of not producing the fluid pressurization or producing the fluid pressurization less than that of the surrounding rock, becomes the collecting zone of natural gas migration, which makes potential of the fault zone higher. Tectonic compression lets to the strata producing fractures and faults opening, makes the vertical gas potential gratient be greatly bigger at the same time and enhances the vertical migration force of natural gas from the lower source rock along the opening faults. The accumulation gas near the fault zones rapidly migrates towards upper strata along the opening faults and charges laterally the sand bodys located under the regional cap rock, accumulates in the lower gas potential area. The faulted anticline and the anticline located under the gypsum—salt strata in Kuqa foreland thrust belt is the lower gas potential area in the later Himalayan period, is also the place that has the opening oil source fault and where the vertical gas potential gratient has be greatly bigger and has good preservation conditions, becomes the favorable gas accumulation area. The strong tectonic compression in the foreland basin of the central and western China has significant impact on the natural gas accumulation. So the study for impact of tectonic compression on natural gas accumulation has important theory and application for guiding oil and gas exploration in foreland basin.