Geological features of Mesozoic lacustrine shale gas in south of Ordos Basin, NW China

The geological characteristics of Mesozoic lacustrine shale gas are summarized from the following aspects: distribution of shale, geochemistry of shale gas, characteristics of shale reservoir, enrichment form of shale gas etc, based on the lacustrine shale gas exploration research and practices in southeast of the Ordos Basin. The geochemical characteristics and thermal evolution degree of shale gas source rocks are controlled by the evolution of lacustrine basin in the early and middle stages of late Triassic Period, and the main hydrocarbon-generation rocks are shale from the Chang 7 and Chang 9 members of the Triassic Yanchang Formation, with high abundance of organic matter and in the mature to wet gas stage. The most mineral compositions are quartz, feldspar and clay mineral in shale gas reservoir, and the primary intergranular pores and secondary dissolution pores are the main pore types. The shale gas in the study area is oil-type gas, dominantly wet gas. The shale gas occurs mostly in the adsorption state, the free state and the dissolved state. Estimated by the volumetric method, the total shale gas resources of Chang 7 is 5 318.27x10(8) m(3), and the total shale gas resources of Chang 9 is 3 067.29x10(8) m(3).