川西前陆盆地天然气成藏过程

The gas accumulation process in Western Sichuan Foreland Basin

川西前陆盆地具有丰富的天然气资源,发育上三叠统巨厚的煤系烃源岩,以生气为主,并发育多套储盖组合。天然气成因类型主要是煤成气,目前的气田分布主要受古隆起、沟通下部烃源岩和上部储集层的隐伏断层以及储集条件的控制。川西前陆盆地具有多期成藏、燕山期或喜山期聚集、喜山期调整等特点。来自上三叠统煤系源岩的天然气聚集主要在燕山期,形成原生气藏或下生上储型气藏;后经过喜山期的逆冲作用,对浅层储集层进行改造,产生的断裂沟通深部气藏与浅层圈闭,在对深层(主要在上三叠统)原生气藏进行改造的同时形成浅层(侏罗系)次生气藏。

The Western Sichuan Foreland Basin developed Upper Triassic coal measure source rock, which mainly generated gases. There exist several reservoir-cap combinations for natural gas preservation. So the Western Sichuan has abundant natural gas resource. The gases belong to coal-typed and the occurrence conrolled by paleo-uplift, the buried gas source faults that connect the source rock and reservoir and the beneficial reservoirs. The Southern Sichuan Foreland Basin had endured several times of gas accumulation. The gases mainly accumulated during Laramide and Himalaya orogenies, gas pool adjusting during Himalaya. Gases from Triassic coaly source rock accumulated during Laramide and original gas pool formed. During Himalaya, thrusting movement promoted the shallow reservoir storage ability. The faults produced acted as pathway in connecting shallow traps and some deep gas pools. In this way, the deep original gas pool, mainly Upper Triassic gas reservoirs, had been adjusted and shallow gas pools had been formed in the Jurassic at the same time.