| The Lower Paleozoic marine shale in the southern China has undergone CaledonianHimalayan multi-stage tectonic deformation,with strong uplift and denudation,welldeveloped faults,and shale gas cannot be continuously accumulated in a large area.The production of different blocks and different structrual belts in the same block varies greatly.Exploration and development practice shows that preservation conditions are the key to shale gas enrichment and high yield.In this paper,the Changning and Luzhou Blocks in the southern Sichuan Basin are taken as the research objects to carry out comprehensive research on detailed ground geological survey,fine structural interpretation of seismic data,observation of natural fractures in shale,and U-Pb dating of calcite in fault zones.The deformation characteristics and deformation stages of structures in different directions are clarified,and the development characteristics and distribution rules of multi-scale fault systems are clarified.On this basis,the evaluation parameters are optimized,and the comprehensive quantitative evaluation system of preservation conditions is established,which provides theoretical and technical support for increasing production and efficiency of shale gas in the southern Sichuan Basin.The structural features of the Changning Block are both NW to near E-W and NE,and the structural style is mainly fault-related fold.The fault development grade span is large,which can be divided into grade I,II,III and IV fault;in the block,the fracture development degree of Tiangongtang anticline and Shuanglong syncline is the highest,mainly through the layer shear fracture,followed by Jianwu syncline and Luochang syncline.The main tectonic deformation stages are early Yanshanian and late Yanshanian.The structural features of the Luzhou Block are NE-trending to nearly S-N-trending,and the structural style is a typical barrier fold;there are few large fault,mainly developing grade II,III and IV fault.The fracture development degree of Fuji syncline in the block is the highest,and the main fracture type is intra-layer tensile fracture.The fracture density of Desheng-Baozang syncline and Laisu-Yunjin syncline is low.The late Yanshanian and Himalayan periods are the main tectonic deformation periods.The preservation conditions of the Longmaxi Formation shale gas in the Changning and Luzhou Blocks were comprehensively evaluated and partitioned by optimizing structural transformation time,structural style,uplift and erosion,stratigraphic dip angle,multi-scale fault-fracture and current in-situ stress.The results show that the preservation conditions of Jianwu syncline and Luochang syncline in Changning block are better,and the preservation conditions of Tiangongtang anticline and Shuanglong syncline are medium.Fuji syncline and Desheng-Baozang syncline in Luzhou block have good preservation conditions,while Laisu-Yunjin syncline has medium preservation conditions. |
