Study On The Preservation Conditions Of Shale Gas In Lower Paleozoic In Northeast

This thesis takes shale of the Lower Paleozoic Cambrian Shuijingtuo formation and Upper Ordovician Wufeng formation-the Lower Silurian Longmaxi formation in the northeast area of Chongqing as an object to analyse the preservation conditions of structure of shale gas. It gives reference value to the exploration prospect of shale gas of the northeast of Chongqing.According to the reference, I can divide the evolution of tectonic and sedimentary of Chongqing into Yangtze paraplatform fold basement formation stage, Geosyncline-Geoanticline stage and Intracontinental transform stage. The sedimentary rock in the northeast of Chongqing, with exception of Devonian, Carboniferous, Paleogene and Neogene, the stratum which are developed from Mingyue formation of Neoproterozoic to Quaternary are exposed.Takes Chengkou fault as the boundary, I can divide arc structural zone of daba mountain into some tectonic units, including north daba thrust nappe tectonic zone and south daba composite foreland fold-thrust zones. According to the kinematic characteristics and deformation characteristics, the combination of fault and fold types and its development degree, it can be divided into some secondary tectonic units.The main tectonic style features of the north area of Chengkou fault in the northeast of Chongqing is significant development of fault and fold, forming the half flower shape tectonic, developing a series of longitudinal fault and extension towards the northwest and be cut-off by the fault of Chengkou. Basing on the surface geological investigation, and taking Lowell" and "Harding" as a classification of structural styles, I conclude that the main tectonic styles of the south area of Chengkou fault in the northeast of Chongqing is "thrust-fold assemblage" of "capping-sliding type".It has developed three kinds of structural assemblages, they are thrust fault system, thrust fold system and detachment fold system. On the transverse, taking Pingba fault and Jimingshi fault as the boundary, there are some typical structural combinations of imbricate thrust zone, thrust fold zone and decollement fold zone. On the longitudinal, taking gypsum-salt rock strata in Triassic and mudstone in Silurian as the boundary, there are some typical structural combination of lower, medium and upper structural layers. The imbricate thrust zone is dominated by the fracture, rather than the fold. Imbricate thrust fault, recoil fault, pop up structure, triangle zone and duplex structure are common. The development of fault and fold are roughly equivalent, fault related fold is common. The detachment folds are mainly developed in the detachment fold zone, thrust fault is rare, one principal characteristics of this region is the typical domal structure. According to the observation of the field outcrop, cores and the thin sections under microscope, fracture development can been seen, it does dual effect on the preservation of shale gas.According to the field geological survey and measurement, mud shale strata in Shuijingtuo formation has a high effective thickness, generally between62m-253m; Mud shale strata in the Wufeng formation-Longmaxi formation of Lower Silurian has a generally high thickness, between25m-73m in.According to the analysis of tectonic feature and the cap rock of shale gas of lower Palaeozoic, we can find out the good preserved structural areas of shale gas of lower Palaeozoic Shuijingtuo and Longmaxi formation in the northeast of Chongqing. We can select four areas of the good preserved structural areas of Shuijingtuo formation, they are near the Manyuexiang-Liaozixiang and Fenhe-Miaotangxiang-Yuanyangxiang. The good preserved structural areas of shale gas of Wufeng formation-Longmaxi formation are near the Wuxixianshuixiang-Longtaixiang and Fengjie, which could be served as outstanding exploratory areas in the future.