四川盆地开江古隆起形成演化及其对天然气成藏的控制作用

开江古隆起是四川盆地内的三大古隆起之一,也是川东地区天然气勘探的重要领域,前人的研究重点分析了印支期古隆起的形态,未系统阐述古隆起的形成演化过程及其对气藏形成的控制作用。为此,基于区域地质、野外露头与钻井等综合资料,分析了不同构造期该古隆起的平面展布特征,探讨了古隆起形成演化对烃源岩发育、储层发育以及天然气分布的控制作用。结果表明:该古隆起的形成演化经历了以下4个时期:①云南运动期,古隆起初具雏形,形成开江、梁平2个隆起高点,呈南北向展布;②东吴运动期,古隆起继承发育,隆起范围扩大并呈北西西向展布;③印支运动期,古隆起最终定型,隆起范围进一步扩大,并呈北东向展布;④燕山期—喜马拉雅期,古隆起发生解体形成现今构造面貌。结论认为:开江古隆起是因不同地质历史时期基底差异区域抬升、强烈拉张作用与板块俯冲远端效应的综合作用而形成,其形成演化对该区上二叠统龙潭组烃源岩展布和石炭系岩溶储层发育以及石炭系—三叠系天然气的分布具有明显的控制作用。

Formation and evolution process of Kaijiang paleohigh in the Sichuan Basin and its controlling effects on gas pool formation

As one of the three paleohighs in the Sichuan Basin, Kaijiang paleohigh is an important gas exploration area in the eastern basin. Previous analysis focused on its form during Indosinian, but no systematic illustration was ever performed on its formation and evolution and its controlling effects on the formation of gas reservoirs. Therefore, the areal extension characteristics of Kaijiang paleohigh in different tectonic periods were analyzed based on the data in regional geology, field outcrop and drilling, and the controlling effects of its formation and evolution on source rocks, reservoir development and gas distribution were discussed. It is shown that its formation and evolution is divided into four stages. The first is the Yunnan Movement stage, when the paleohigh was preliminarily in embryonic form and Kaijiang and Liangping uplift highs were formed and extended in north-south direction. The second is the Dongwu Movement stage, when the paleohigh was inheritedly developed, enlarged and extended in northwest-west direction. The third is the Indosinian Movement stage, when the paleohigh was finally fixed, enlarged and extended in northeast direction. And the fourth is the Yanshan-Himalayan stage, when the paleohigh was presented in current structure form after its dismembering. It is concluded that Kaijiang paleohigh was formed under the joint effect of regional uplifts (formed by basement difference at different geologic stages), strong tension force and plate subduction distal effect, and its formation and evolution exerts a controlling effect on the extension of Upper Permian Longtan Formation source rocks, the development of Carboniferous karst reservoirs and the distribution of Carboniferous-Triassic gas reservoirs.