Study on the characteristics of in-situ gas desorption from the Wufeng - Longmaxi shale in the Sichuan Basin

Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation shale in the Sichuan Basin and its periphery is an important horizon for shale gas exploration and development in my country. The rapid on-site desorption instrument independently developed by Sinopec Wuxi Institute of Petroleum Geology was used to test the desorption gas volume, lost gas volume, total gas content, natural gas components of desorbed gas and carbon isotope of methane in typical shale gas wells in this area. Data analysis shows that the carbon isotope value and characteristics of the first sample of methane can predict shale gas enrichment layers, and the total gas content and desorbed natural gas components can identify shale gas sweet spots; shale gas components and carbon isotope values can jointly identify shale gas Genesis type, kerogen carbon isotope characteristics and shale gas carbon isotope characteristics can be used as effective means for gas source comparison; shale gas composition characteristics can distinguish the preservation conditions of the area, which are indicative for the study of the degree of shale gas loss; The combined application of total gas content and initial dissipation index can better identify the sweet spots of shale gas, and avoid single-factor identification of sweet spots; the carbon isotope value of methane shows obvious fractionation effect with desorption time, which can predict shale gas production stage and residual gas content.