Shale-gas hydrocarbon generation and accumulation conditions of the Jurassic strata in southern Altun Mountains

Jurassic strata, which are well developed in southern Altun Mountains, have good oil and gas generation conditions; never-theless, no investigation and evaluation for shale gas have been carried out in this region. Based on field geological survey and sample test, the authors investigated the thickness and sedimentary environment of Jurassic shale and analyzed the geochemical and reservoir property conditions of shale gas. The results show that the total thickness of Jurassic mudstone is 158~250m with the largest single thickness up to 89 m. Sedimentary environment is deep lake and semi-deep lake depositional facies. Organic carbon content is 0.15%~7.96% with an average of 2.05%. Vitrinite reflectance is 1.02%~2.50% with an average of 1.41%. Kerogen types are mainly typeⅡ₁ and typeⅡ₂. The shale layers also contain high content of brittle minerals(>43%), with effective reservoir space well developed in the shales. The comprehensive analysis indicates that the Jurassic shale in southern Altun Mountains has basic geological conditions for shale-gas generation and accumulation.