四川盆地东南缘下古生界页岩气差异强改造保存机理研究

The southeast area of Sichuan Basin is one of the most abundant area of marine shale gas resource in the Lower Paleozoic in China. This area has experienced cycles and stages of structural overlap and rework. The marine shale in the Lower Paleozoic has experienced the changes of physical parameters, temperature, pressure during the deeply buried and high matured early-middle stages. These significantly influence the gas bearing and degree of enrichment of shale gas. The changes of regional energy field by different rework of structural deformation, faults, uplift, erosion during the late stage during the Yangshanian and Himalayan period ,bring about the changes of shale gas accumulation conditions of adsorption and desorption, fluid flow and diffusion, cause the adjustment of the preservation and distribution of shale gas, and control differences of the shale gas accumulation in inner zone and the outer zone in the Southeast Area of Sichuan Basin, Fuling block in inner zone being a high production area and Pengshui block and so on in outer zone being a low production area or nothing areas. Studies on preservation mechanism of shale gas of differently high tectonic-rework in the southeast area of Sichuan basin not only answer the scientific issues about accumulation rule and preservation of shale gas of the marine shale in the Lower Paleozoic in the southeast area of Sichuan Basin, but also give the example and the basis of the shale gas effective exploration. This studies will make innovations of shale gas accumulation theories.

四川盆地东南缘是中国下古生界海相页岩气资源最丰富的地区之一。该地区经历了多期次多旋回构造叠加改造作用,区内下古生界海相页岩经历了早、中期深埋藏和高演化引起的物性参数、温度、压力等变化，对下古生界黑色页岩的含气率和富集度有重要影响，而在晚期的晚燕山-喜山运动中,受构造变形、断裂、隆升、剥蚀等强烈差异性改造引起的区域能量场变化，致使页岩气吸附/解吸、渗流/扩散等成藏条件发生变化，从而导致盆地东南缘由内而外下古生界页岩气的保存和分布产生重大调整，形成直接控制内带和外带页岩气差异性富集成藏的关键因素，其中内带涪陵区块龙马溪组页岩气勘探取得重大突破已成高产区，而外带彭水等区块仅获得低产气流。因此，开展页岩气差异强改造保存机理研究，不仅解答了四川盆地东南缘下古生界海相页岩气富集规律和保存条件等科学问题，为同类地区的页岩气高效勘探提供范例和依据，缓解中国能源供应紧缺形势，同时在页岩气成藏理论上有所创新。

项目通过四川盆地东南缘关键页岩气钻井下古生界富有机质页岩岩心（屑）及地表构造剖面系统，研究了四川盆山东南缘结构-构造、变形样式与变形强度、抬升剥蚀、流体地球化学特征等，研究了川东南地区下古生界页岩层系强隆升、强剥蚀和强变形作用的差异性，研究了页岩层系宏观-微观参数特性, 探讨了川东南地区(盆内和盆外)下古生界页岩气的富集机理和保存条件。具体四个方面的研究工作：（1）四川盆地东南缘盆-山结构-构造变形特征研究；（2）关键钻井地区下古生界页岩强隆升-强剥蚀构造（热）过程研究；（3）关键钻井和露头剖面下古生界页岩流体地球化学特征研究；（4）强隆升、强剥蚀、强变形构造背景中下古生界页岩气保存条件综合研究。项目取得如下结果：四川盆地东南缘二叠系-下三叠统的流体活动以内源流体为主，表明其具备封闭能力；隆升剥蚀过程中温压场的调整会对裂缝的生长和扩展起到积极作用，裂缝持续生长并彼此连通后，致中寒武统-奥陶系间跨层流体活动，下寒武统筇竹寺组页岩之的下古生界上覆盖层的封闭性较差；五峰组-龙马溪组泥页岩的顺层滑脱致使上下构造层发生解耦，顺层滑脱面是重要的应力释放区（或者应力释放面），滑脱冲断作用比滑脱作用具有更强的破坏性；滑脱作用主导的构造部位（简称滑脱区）比逆冲作用主导的构造部位（简称逆冲带）具有更好的勘探前景。盆外隔槽式褶皱区源于基底滑脱面和寒武系滑脱面的逆冲断层较盆内更加发育，促使下古生界跨层流体活动增强，外带页岩气保存条件较内带差。项目研究成果部分解答了四川盆地东南缘下古生界海相页岩气富集规律及保存条件，支持了四川盆地川东南部的页岩气勘探。