Geological conditions of the Jurassic shale gas on the northern margin of Qaidam Basin

Jurassic shale is one of the main hydrocarbon source rocks in Qaidam Basin and possesses the geological conditions for the formation of shale oil and gas. Eleven samples collected from the surface outcrops of Jurassic shale near some coal mines on the northern margin of Qaidam Basin such as Yuqia, Dameigou, Xiaomeigou, Kaiyuan, Lvcaogou and Datouyang. The authors carried out single multi-parameter experimental analysis of these samples and investigated the relationship between the organic geochemstry, petrophysical properties and gas content of lacustrine shale. On such a basis, the shale gas resource evaluation parameter system was established. The results show that the northern margin of Qaidam Basin was characterized by shallow lake-semi-deep lake lacustrine sediments in Jurassic, with well-developed fractures. During that time, shale was rich in organic matter, and had such characteristics as low porosity, low permeability, low maturity, low brittleness, and high gas content, thus having geological conditions for the formation of shale oil and gas. Further exploration and development of Jurassic shale should choose shale gas areas with high formation pres-sure coefficient, relatively favorable storage conditions and high content of brittle minerals.