Prospecting Potential and Accumulation Conditions of Shale Gas in the North of Ordos Basin, North China:Taking the Taiyuan and Shanxi Formations as Examples

The Taiyuan and Shanxi formations have great shale gas exploration potential in the northern Ordos Basin. With the geological and geochemical analysis, the shale of Shanxi and Taiyuan formations were studied with the sedimentary facies characteristics, TOC, organic carbon type and maturity. With the NMR logging and field desorption experiment, the reservoir characteristics and shale gas concentration were analyzed in the two formations. The results showed that the shale is well developed thickly and distributed in the two sections of Taiyuan formation and the upper two sections of Shanxi formation. The siltstone or sandstone sandwiched with the mudstone has favorite reservoir space for shale gas. The shale has high content of humic organic matter, which now benefits for generating gas at the maturity stage and over-mature stage. The Taiyuan mudstone is brittle with more quartz, while the Shanxi mudstone has more clay content with micro pores. The clay mineral of two formations primarily consists of the kaolinite and illite. The reservoir space includes the matrix pores and fractures decided by the development degree of pores and fractures. The Taiyuan formation has higher gas content than Shanxi formation including the shale and the sandstone, especially higher gas content in the coal.