Analysis on geological conditions of shale gas accumulation in Lower-Middle Jurassic strata of Southern Altyn Tagh

There are some thick layers of dark muddy-shale in Jurassic strata of Southern Altyn Tagh, which have high hydrocarbon potential and formation conditions of continental shale gas. So this area is an advantageous succession area for exploration. Based on the field geological investigation and sample collection and test,the distribution of Lower-Middle Jurassic sedimentary facies, organic geochemical characteristics, reservoir properties and exploration potential of shale gas in this area have been discussed in this paper. Organic rich shales were mainly developed in the shallow-deep lake and swamp environment. The shales distribute as NE trending with large single-layer and cumulative thickness. The kerogen types of organic matter are mainly Ⅱ₁ and Ⅱ₂. The total organic carbon (TOC) content varies from 0.55% to 10%, with the average of 2.28%. R_O varies from 1% to 1.6%, with the average of 1.269%, from mature stage to high mature stage. These are the good hydrocarbon generating conditions for shale gas reservoir. The shales are characterized as high content of brittle minerals, more than 51%, which are conducive to hydraulic fracturing and shale gas exploitation. Shale reservoir developed micro pore and fracture that were shown under scanning electron microscope, which provided space and great migration channel for shale gas. For preliminary forecast, Yueyashan region with relatively weak rock deformation is favorable exploration area of shale gas.