准噶尔盆地南缘中下侏罗统煤系烃源岩生气史

Gas-Generating History from Middle-Lower Jurassic Coal Measures in Southern Margin of Junggar Basin

利用化学动力学方法,以西山窑组煤成气为例,模拟计算了准噶尔盆地南缘地区中下侏罗统煤系烃源岩的生气过程。结果表明,该区中下侏罗统煤系地层主要生气期为燕山运动期,约占最终生气量的80%,并以白垩纪为主。因此,对应绝大部分天然气的生成,燕山运动形成第一排背斜圈闭对该中下侏罗统煤成气成藏意义重大。而喜马拉雅运动则最终决定该区天然气的成藏条件:一方面对第一排背斜圈闭的构造调整(包括油气在原生油气藏中的继续保存和向次生油气藏的转移)在很大程度上决定了该区天然气的资源前景;另一方面所形成的第二、第三排背斜圈闭可聚集烃源岩晚期热解及原油二次裂解所生天然气。

The process of natural gas generation from the Middle-Lower Jurassic coal measures in the southern margin of Junggar basin is simulated with chemical kinetic method by taking the coal-derived gas of Xishanyao formation as an example. The results indicate that the gas generation occurred mainly in Yanshan movement period, accounting for about 80% of the final gas amount, dominated by the period of Cretaceous. Corresponding to the most natural gas generation, the formation of the first-line anticlinal traps in Yanshan period is very significant. Moreover, the Himalayan movement decides the reservoir-forming condition of natural gas in this area. On the one hand, the tectonic adjustment on the first line anticlinal traps （including the continuous conservation of oil and gas in primary reservoirs and the migration toward secondary reservoirs） decides the resource perspective of natural gas in this area to a great extent. On the other hand, the second and third line anticlinal traps formed during the movement can accumulate the natural gas from the late pyrolysis of kerogen and the second cracking of crude oil.