The main controlling factors of the gas content in the Permian Dalong Formation of the Xuanjing area, the lower Yangtze region: a case study of Gangdi 1 Well

There are three favorable shale reservoirs developed in Cambrian, Silurian and Permian in the lower Yangtze region. Even though with great gas potential, the main controlling factors of shale gas content are not yet clear. Therefore, based on the Gangdi 1 Well in the Xuanjing area of the Lower Yangtze region, we took the drilled 70 m shale of the Late Permian Dalong Formation as the target layer for core sampling, and made continuous and dynamic studies on mineral composition, pore structure, Total Organic Carbon, vitrinite reflectance(Ro) and organic matter types in vertical direction by comparative analysis. The corresponding relationship between gas content and geochemical indicators, namely TOC, Ro and organic matter type were further researched and accordingly the key geochemical parameters affecting the gas content were determined. Analysis results show a strong positive correlation between TOC and shale gas content, and a relatively weak correlation between Ro and gas content in the middle process of organic matter maturation, which less affected the gas content change. At the same time, organic matter type has an important impact on shale gas content, but the correlation is weaker than that with TOC. Through systematic analysis on Dalong Formation shale from top to bottom,we figure out a new method to analyze the factors that affect gas content in the vertical direction.