Gas bearing analysis of continental shale of Chang 7 member of Yanchang formation in Yanchang oil & gas region of Ordos basin

By means of gas logging, geochemical analysis and field desorption test, it is proved that it is feasible to qualitatively judge the gas-bearing properties of shale by gas logging data. For the continental shale of Chang 7 member in Yanchang oil & gas region, the qualitative analysis of gas-bearing properties is carried out in east-west and north-south directions. The lost time in field desorption experiment of shale is reanalysed and determined. The lost time in the process of lifting drill by USBM method is corrected, and an improved USBM method is proposed to recover the lost gas. Through field desorption experiments, the gas content of Chang 7 shale is quantitatively characterized. The total gas content is 1.87～5.23 m~3/t, and the average gas content is 3.51 m~3/t. The desorption gas content is 0.28～2.14 m~3/t, the loss gas content is 0.49～4.34 m~3/t, and the residual gas content is 0.17～0.61 m~3/t. The overall gas content of Yanchang formation shale is not high and its gas abundance is low. The total gas content has an obvious increasing trend with depth, which is consistent with the qualitative analysis results.