Characteristics of the shale gas reservoirs and evaluation of sweet spots in Wufeng Formation and Longmaxi Formation in Jingmen exploration area

In order to further clarify the resource potential of shale gas from Wufeng Formation to Longmaxi Formation in Jingmen exploration area, sweet spots were selected. The shale in Wufeng Formation and 1th Member of Longmaxi Formation of the well X was taken as the research object in this study. Using sliced kerogen, X-ray diffraction, nuclear magnetic resonance, micro nano CT scanning, geochemical analysis and other testing methods, combined with logging interpretation results, based on the petrology, organic geochemical and mineral composition, physical properties, pore types and structure characteristics and hydrocarbon content, the reservoir characteristics of Wufeng-1^th Member of the Longmaxi Formation were evaluated, and the longitudinal shale gas sweet spots were optimized. The results show that: (1) Wufeng-1^th Member of the Longmaxi Formation is mainly composed of siliceous shale mainly forming the reduction environments in the deep shelf facies. The natural gas in the high-quality shale section has high natural gas quality and excellent organic geochemical characteristics; (2) There is a positive correlation between porosity and permeability measured by various methods. The NMR T2 spectrum of water -saturated shale can be divided into 2 types and 5 types. The pore size distribution of shale reflected by different types of T2 spectrum is different. The isolated pores mainly exist in micropores smaller than 2 nm, which accounts for a very small proportion; (3) Based on the comprehensive evaluation of reservoir characteristics Long _1^1- Long _1^2 layer were selected as type I reservoir, the upper Wufeng Formation and Long _1^3 layers were classified as type Ⅱ reservoirs, and Long _1^4 layer as type Ⅲ reservoir. The upper Wufeng Formation-Long₁³ small layer (about 17.7 m thick) namely carbon-rich high silicon shale section is a shale gas sweet spot. The research results can provide a reference for determining the horizontal well target segments for shale gas exploration and development in Jingmen exploration area.