Shale gas composition and gas bearing characteristics of Wufeng-Longmaxi For-mation in Zheng'an area,Guizhou Province
Seven shale gas core wells in Wufeng-Longmaxi Formation in Anchang syncline in Zheng'an area of Guizhou Province are selected as the research objects.Through field analysis and composition analysis of shale gas samples,the composition characteristics and gas-bearing characteristics of shale gas in Zheng'an area are expected to be understood.The results show that methane is the main component of shale gas in Wufeng-Longmaxi Forma-tion,with an average content of 98.33%.The helium content is between 0.06%and 0.07%,reaching the stand-ard of helium fields.The total gas content is 1.64 m3/t to 5.88 m3/t,with an average of 3.02 m3/t.The gas content decreases gradually from the central part of the syncline to the north and south ends,and decreases gradually from the core of the syncline to the two wings.The total gas content increases with depth and reaches its maximum at the bottom of Longmaxi Formation.The desorption gas accounts for 31.3%to 66.7%of the total gas content,and the loss gas accounts for 32.5%to 66.0%.Wells Ay1 and Ay4 located in the syncline core have the highest swing-to-suction ratio,which is 1.39 to 5.49,with an average of 2.20.They have better preservation conditions and re-coverable ability.The overall gas saturation is high,which is 58.85%to 86.18%,with an average of 75.60%.The resource prospect is good.