内蒙古西部额济纳旗及邻区石炭系-二叠系沉积后的构造演化、盖层条件与油气信息——石炭系-二叠系油气地质条件研究之三

摘要

Based on an analysis of Mesozoic-Cenozoic sedimentary evolvement and a study of structural reformation after Carboniferous-Permian and Mesozoic magmatism, the authors hold that Cretaceous was a flourishing period of Yingen-Ejin Benner basin evolution: there existed the combination of lacustrine facies-swamp facies sandstone and mudstone characterized by large thickness and stable horizontal spread, and Cretaceous mudstone consitituted a good regional cap of the Carboniferous-Permian petroleum system.Although multistage tectonic reworking took place after Carboniferous-Permian, tectonic stress was dominated by extruding and uplifting.In general, the extrusion and uplift didn't affect the Carboniferous-Permian petroleum system except for local areas where structural dynamometamorphism occurred.There happened four stages of magmatism, in which the Early Cretaceous magmatism was strong.Affected by this magmatism, Carboniferous-Permian strata locally experienced thermal metamorphism, and hydrocarbon source rocks reached the mature stage, but the effect range was limited.There were four sedimentary cycles during Carboniferous-Permian;as a result, there existed mud shale of large thickness and stable horizontal spread especially in Amushan and Maihanhada Formations,and the mud shale was not only a good source rock but also a good cap rock.There was a long-term uplift-erosion from Late Variscan to Indo-Chinese epoch in Carboniferous-Permian, but there existed stable spread of Carboniferous-Permian strata in Ejin Banner-Wutaohai area based on geophysical data interpretation, with the residual thickness being generally from 1000 to 2000m and the thickness of local areas being over 3000m.Information of a series of Carboniferous-Permian hydrocarbon source rocks related hydrocarbon shows indicate that there existed processes of hydrocarbon generation, migration and accumulation in Carboniferous-Permian period, which suggests good hydrocarbon prospects.%通过对中-新生代沉积演化特征的分析和对石炭系-二叠系沉积之后构造改造作用、中生代岩浆作用的研究,认为白垩纪为银根-额济纳旗盆地演化的鼎盛时期,沉积了厚度大、横向分布稳定、以湖泊-沼泽相为主的砂泥岩组合,是石炭系-二叠系油气系统的良好的区域盖层.虽然石炭系-二叠系沉积之后经历了多期次的构造改造作用,但构造应力以挤压抬升为主,除局部地区发生构造动力变质作用外,总体对石炭系-二叠系油气系统保持条件的影响不大.中生代经历了4个期次的岩浆活动,早白垩世岩浆活动较强烈,受其影响石炭系-二叠系局部发生热接触变质或烃源岩演化达到过成熟,但影响范围有限.石炭系-二叠系内部发育4个沉积旋回,尤其是阿木山组、埋汗哈达组发育厚度大、横向分布稳定的泥页岩,既是良好的烃源岩,也是良好的盖层.石炭系-二叠系沉积之后虽然经历了华力西末期-印支期的长期抬升剥蚀,但地球物理资料显示石炭系-二叠系在额济纳旗-务桃亥一带分布较为稳定,残留厚度一般1000～2000m,局部厚度大于3000m.油气显示信息表明,石炭系-二叠系具有油气生成、运移与聚集的过程,油气资源前景良好.