Characteristics and distribution pattern of shale gas reservoir in Longmaxi Formation in Guizhou Province

The work of geology survey and investigation on shale gas has been done to reasonably evaluate the gas resource potential of Lower Silurian Longmaxi Formation. It has been shown by the research that Longmaxi Formation in Guizhou Province mainly distributes in areas north of Zunyi-Yuqing where Ⅰ-type kerogen and Ⅱ₁-type kerogen in the shale predominate and the content of organic carbon in the shale is usually under 2%, with the R_o between 1.5% to 3.39% and the lower part of the formation has higher organic matter maturity. As it formed majorly by detrital minerals and clay minerals, shale shows strong brittleness. Porosity in shale develops comparatively well and the major fracture, micro fracture together with pore and fracture between clay mineral layers form good desorption-seepage channels. Compressive strength is significantly different from tensile strength, while water medium has no obvious effect on the intensity of shale. Shale gas contents are in the range of 0.63~2.81 m³/t, which show increasing trend with the increase of depth. Yangtze platform suffered multi-stage tectonic transform, which caused strong effect on the reserve of shale gas in Longmaxi Formation and the excellent shale gas reservoirs in Guizhou Province mainly distribute in areas north of Zhengan-Wuchuan-Yanhe.