| Summary: | The reservoir characteristics of marine-continental shale gas in the Upper Permian Longtan Formation in the western Guizhou province were studied using X-ray diffraction, organic geochemistry, scanning electron microscopy, nitrogen adsorption, gas content determination and isothermal adsorption analyses of shale samples from some characteristic wells. The shale in the Longtan Formation in the study area has a large overall thickness, but there are many layers and each layer is thin. The clay mineral content is the highest, followed by the quartz content. The vitrinite group is dominant in the kerogens, which are mainly of type Ⅲ. The TOC content is generally greater than 3.0%. The Ro value averages 1.01%, showing a relatively lower maturity, mainly at the gas generation peak. The reservoir has ultra-low porosity and ultra-low permeability. Intergranular, intragranular and organic pores as well as micro-fractures were observed. A large number of nano-scale pores and fractures were present. Meso-pores are dominant, shaped like narrow-necked and wide-body ink bottles or narrow pores. Large specific surface area, total pore volume, pore fractal dimension and correlation coefficient indicate that the shale has a rough surface, poor connectivity, and strong heterogeneity. The on-site analysis of shale finds high total gas content and strong adsorption, and the interbedded coal seams show high gas content, indicating a large resource potential. The geological conditions and enrichment space are favorable for shale gas in the study area, and effective reservoir reconstruction technology can be selected for coalbed mining.
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