An analysis of the genesis and geochemical characteristics of shale gas in Lower Jurassic Beipiao Formation in Jinyang Basin

The Jinlingsi-Yangshan Basin (Jinyang Basin) is one of the basins with the most completely Jurassic strata in northern China. The Lower Jurassic Beipiao Formation in the basin is composed of a set of lacustrine mudstones, and has beneficial potential of oil and gas. There are four wells in the west of the Zhangjiyingzi depression of Jinyang Basin, of which oil and gas shows were found in three wells. Field desorption of drill core from the SZK2 and SZK3 wells shows that the shale gas content collected from the shallower strata of mud shale of Beipiao Formation is considerable with the increasing depth, the total gas content and methane content increase. In addition, the total gas content and organic carbon content show a good positive correlation, which is a key factor affecting the gas content of the shale. A comparison with characteristics of adsorbed gas carbon isotope of the shale shows that the gas mainly came from biogenic gas and coal gas, and the shale gas has the characteristics of hybrid origin. The X diffraction analysis of mud shale from Beipiao Formation indicates that the favorable conditions of fracturing and strong gas adsorption capacity result in the good prospect of shale gas exploration. Beipiao Formation is favorable for shale gas exploration.