四川盆地叠合演化与油气聚集

Superposed evolution of Sichuan Basin and its petroleum accumulation

根据前人成果和石油勘探资料,对赋存在扬子板块上的四川盆地进行了解剖,认为盆地经历了震旦纪、寒武纪—志留纪、石炭纪—二叠纪—中三叠世、晚三叠世—侏罗纪—早白垩世和晚白垩世—新生代盆地沉降、隆升剥蚀五大构造演化阶段。震旦纪、寒武纪—志留纪盆地演化阶段受周缘断陷的控制,以碎屑岩、膏盐岩和碳酸盐岩建造为特征,盆地基底整体表现为西高、东低的构造格局。中奥陶世末的构造事件形成了川中古隆起,志留纪末的构造事件导致了盆地的整体隆升与剥蚀。在经历了志留纪末期的构造变形、隆升改造后,石炭纪—中三叠世进入陆表海盆地演化阶段,以碳酸盐岩和膏盐岩建造为主要特征,整体表现为西南隆、东北降的构造格局。茅口组沉积末的构造事件导致了盆地隆升和剥蚀,中三叠世末的构造事件形成了泸州—开江古隆起,盆地消亡,地层遭受剥蚀。晚三叠世前陆盆地叠合在前期海相盆地之上,导致了盆地西低、东高的构造格局,侏罗纪—早白垩世表现为大型陆内坳陷盆地。侏罗纪末的构造事件使川东高陡构造带形成,早白垩世末构造事件导致了盆地的消亡与整体隆升,晚白垩世—新生代盆地沉积在西南部局限分布。盆地叠合演化形成了震旦系、下寒武统、上奥陶统五峰组—下志留统龙马溪组、二叠系梁山组、龙潭组、上三叠统、下侏罗统等多套富含有机质的烃源岩,与盆地内叠合连片发育的中—上寒武统、下—中三叠统、上三叠统、侏罗系和中新统等多套膏盐岩或泥岩、煤系构成了盆地内良好的源-盖组合,成为盆地油气富集的基础。每套优质的盖层之下都发育了一套优质的储层,并与构造作用形成的圈闭形成了盆地良好的储-圈组合,成为油气富集的必要条件,形成了盆地下组合、中组合和上组合三大勘探层系。勘探成果显示,古隆起、古斜坡和烃源岩分布的配置控制盆地的油气分布。

According to previous research and petroleum exploration data, the Sichuan Basin existing in the Yangtze Plate has been researched. The basin has undergone five evolution stages： Sinian faulted basin evolution, Cambrian-Silurian faulted basin evolution and inversion, Carboniferous-Permian-Middle Triassic basin evolution, Late Triassic foreland basin and Jurassic- Early Cretaceous large intra-continental basin evolution and the Late Cretaceous - Cenozoic uplift evolution. Sinian, Cambrian - Silurian basin evolution was controlled by the peripheral NE-trending faults; basin strata are clastic, evaporite and carbonate rocks; the basement has a structural pattern of west uplifting and east depressing. The late Middle Ordovician tectonic events formed the Chuanzhong Uplift, and the late Silurian tectonic events led to the uplift and erosion of the basin as a whole. After a late Silurian tectonic deformation and uplift, the Carboniferous - Middle Triassic basin was characterized by epicontinental sedimentary evolution of carbonates and gypsum-salt rock; the basement has a structural pattern of southwest uplifting and northeast depressing in this stage. In the end of Maokou sedimentary stage, tectonic events led to the uplift and erosion of the basin; in the end of Middle Triassic, tectonic events formed the Luzhou-Kaijiang palaeohigh. The Late Triassic foreland basin was superimposed on the early marine basins; the basement has a structural pattern of east uplifting and west depressing in this stage. The Jurassic- Early Cretaceous basin is a large intracontinental faulted basin; in the end of the Jurassic, tectonic events formed eastern Sichuan structural zone; in the end of early Cretaceous, tectonic events led to the demise of the basin and the overall uplift. The Late Cretaceous - Cenozoic sediment was confined in the southwest of the Sichuan Basin. The evolution of superposed basins formed several sets of organic-rich source rocks, such as Sinian, Lower Cambrian, Wufeng Formation of Upper Ordovician, Longmaxi Formation of Lower Silurian, Liangshan Formation and Longtan Formation of Permian, coal-bearing formation of upper Triassic and lower Jurassic. The gypsum, salt, mud and coal-bearing rocks developed in the Cambrian, Silurian, Permian, Lower-Middle Triassic, Upper Triassic and Jurassic were distributed with vertical superimposition and horizontal composite joint. These seal and source rocks formed high-quality combinations within the basin, which is the basis of hydrocarbon enrichment. A high-quality reservoir was developed under each set of high-quality cap. The good reservoir-traps combination has become a necessary condition of oil and gas accumulation. There formed lower, middle and upper assemblages of exploration formations in the basin. Exploration results show that the palaeohigh, paleoslopes and ancient source rocks controlled the oil and gas distribution of the basin.