叠合盆地的热演化史与油气生成——以吐鲁番-哈密盆地南部构造带为例

叠合盆地演化的长期性和构造作用的多阶段性,造成盆地内多套烃源岩发育和多阶段的热演化作用,以及油气生成的复杂性。吐鲁番-哈密盆地南部构造带的研究表明,自晚古生代以来,该地区遭受多期次的构造作用与改造。构造热体制和热演化经历了5个不同的阶段,即石炭-早二叠世为伸展裂谷、快速埋藏与超高温阶段,中二叠世为裂谷后凹陷、较快速埋藏与高温阶段;晚二叠世至三叠纪为克拉通内凹陷、稳定沉降与较高温阶段;侏罗纪至白垩纪为广覆式坳陷、稳定沉降与较低温阶段;新生代为挤压造山、较快速沉降与低温阶段。不同地区不同层位的烃源岩具有不同的有机质成熟演化史。台南凹陷二叠系芦草沟组烃源岩和托克逊凹陷中上三叠统小泉沟组烃源岩均具有两次油气生成过程。由于埋藏史和油气生成史的不同,台南凹陷和托克逊凹陷油气藏类型和油气性质出现明显差异。

Thermal evolution history and hydrocarbon generation in superimposed basin:taking the southern structural zone in Turpan-Hami basin, Xinjiang, as an example

Several sets of source rocks have developed and experienced multistage thermal evolution in Turpan-Hami basin, a superimposed basin, as a result of long-term basin evolution and multiphase tectonic activity, thus hydrocarbon-generating history is very complicated. Study of the basin's southern structural belt indicates that this area has experienced multiphase tectonic movements and modifications since Late Paleozoic. Structural thermal system and thermal evolution can be divided into five stages, including an extensional rift stage with rapid burial and super-high temperature gradient from Carboniferous to Early Permian; a post-rift depression stage with relatively rapid burial and high temperature gradient during Middle Permian; an intracratonic depression stage with steady subsidence and relatively high temperature gradient from Late Permian to Triassic; a broad sedimentation stage with steady subsidence and relatively low temperature gradient from Jurassic to Cretaceous; and a compressional orogenic stage with relatively quick subsidence and low temperature gradient during Cenozoic. Source rocks in various horizons and regions have different organic maturation and evolutional history. Both source rocks in Permian Lucaogou Formation in Tainan depression and Middle-Upper Triassic Xiaoquangou Formation in Tuokexun depression have experienced two hydrocarbon-generating processes. The reservoir types and hydrocarbon properties in Tainan depression are obviously different from those in Tuokexun depression, due to differences in burial history and hydrocarbon-generating history.