Abstract:

Shale oil and gas are currently attracting global oil and gas exploration and research interest, however, their potential
evaluation is considered as the main difficulty. The article examines four shale formation in China and North America including Green River Formation lacustrine shale and Niobrara Formation inland marine shale in North America, Longmaxi Formation marine shale and Jiyang lacustrine shale in China. It is found that sedimentary environments are closely related to shale oil and gas potential. Therefore, the shale oil and gas potential can be evaluated by shale sedimentary environment. The four formations shales from China and North America were characterized trace elemental analysis, biomarker compounds, X-ray computed tomography (X-CT) and X-ray diffraction (XRD). Results show that the four formation shales have certain reducing sedimentary environment and high paleoproductivity in Green River formation and Niobrara formation in North America, as well as Longmaxi Formation and shale in Jiyang Depression. As the Niobrara formation shale has dysoxic-suboxic conditions, it has massive layers, lower fracture structure, the lowest organic content and reservoir volume in the four formation shales. The Longmaxi Formation shale is mainly composed of siliceous with high organic content, and the reservoir has more large pore and certain fracture structure, which can be attributed to anoxic marine sedimentary environment. Shales of Green River formations and Jiyang depression have saline source rocks with anoxicsedimentary environment. Shales of the two formations have relatively high organic abundance. Meanwhile, continuous laminae can be clearly seen and the rock is dominated by brittle mineral with abundant fractures. Thus, it can be speculated that shale with an anoxic environment has excellent exploration prospect.

Key words: Shale, sedimentary environment, organic matter enrichment, pore structure, shale oil and gas