Co-exploration potential for coalbed methane and tight sandstone gas in the middle section of the Kele syncline, Northwest Guizhou

Based on the characteristics of multilayer coals and deep main seam for the Late Permian coal-bearing strata in the middle Kele syncline, this paper comprehensively evaluated the co-exploration potential of the "two gases" (i.e., coalbed methane (CBM) and tight sandstone gas) in the terms of depositional environment, reservoir thickness, source-storage configuration and gas content, combining with an exploratory well (X1) of drilling in tight sandstone gas layer. The results showed that:the Kele syncline belongs to the sedimentary facies of meandering river and fluvial delta plain during the Early and Late Longtan periods, which are favorable to the formation of coal and tight sandstone reservoirs. Middle coal group of Longtan Formation is relatively stable, and has cumulative thicknesses more than 16 m and 20 m for coal and tight sandstone layers, respectively, providing a huge reservoir space for the accumulation of CBM and tight sandstone gas. Coal, mudstone and sandstone layers appear in the coal-bearing strata in superposed pattern, which forms several assemblages of "source-reservoir-cap" and has a good configuration relationship between source and storage. According to the well logging of X1, the value of total hydrocarbon is abnormally high up to 78.35%, and gas saturation is about 39.97% and 12.79% for the two tight sandstone layers, respectively. Overall, the study area exhibits a coexistence of "two gases" in the coal-bearing strata.