Characteristics of Permian Marine Shale and Its Sedimentary Environment in Xuanjing Area, South Anhui Province, Lower Yangtze Area

In order to evaluate the shale gas exploration potential of Permian marine shale in the Lower Yangtze region, the shale characteristics and sedimentary environment were analyzed by core photos, thin sections, X-ray diffraction and total organic carbon tests from three drilling cores in Xuanjing area of south Anhui Province. It shows that in Xuanjing area the middle-upper parts of Gufeng Formation are rich in organic matter, and Yinping Formation is a poor organic matter interval. The middle and lower parts of Dalong Formation in the southeast of Xuanjing are high-rich organic matter intervals, and the middle and upper parts of northwest are rich organic matter intervals. In the early stage of Gufeng Formation, with the tectonic subsidence and the seawater deepening, Xuanjing area formed a high biological productivity and anoxic environment formed in Xuanjing area, and a thick siliceous rock layer deposited. In the middle and late periods, the sea level decreased slowly, the living space of organisms decreased, and the sedimentation of high organic matter made the water sulfide, and the TS content increased, and the TOC content reached 10%. During the sedimentary period of Yinping Formation, the sea level dropped rapidly and changed into shallow sea oxidation environment with TOC content less than 1%. In the early stage of Dalong Formation, the position of southeast shallow water slope was affected by upwelling, forming a high biological productivity and anoxic environment, and deposited siliceous rock layer with TOC content greater than 4%. In the middle and late period, the sea level dropped, and the TOC content increased from southeast shallow water to northwest deep water.