页岩沉积环境对其油气潜力的影响:以中国和北美对比研究为例

The Influence of Shale Sedimentary Environments on Oil and Gas Potential:Examples from China and North America

页岩油气是当前全球油气勘探和研究的热点,但其潜力评价一直是难点。该文以中国和北美的四套典型页岩为例,包括北美湖相Green River组、内陆海相Niobrara组、中国环境来评价相龙马溪组和济阳坳陷湖相页岩,发现页岩沉积环境与其油气潜力具有密切关系,因此可通过分析发现这四套页岩的沉积环境都具有页岩沉积环境评价其页岩油气潜力。通过微量元素、生物标志化合物、扫描电镜、X-CT和X射线衍射等方法,发现这四套页岩都具有一定的还原性和较高的生产力,且具有差异性。内陆海相Niobrara组页岩具有弱还原的沉积环境,在四套页岩中有机碳含量较低,呈块状沉积构造,裂缝与微裂缝较少,储集空间相对有限。焦石坝海相龙马溪组页岩为还原的沉积环境,岩石以富含有机质的硅质岩为主,可观察到大量的大孔隙与少量的微裂缝。Green River页岩和济阳坳陷页岩形成于陆相咸化的强还原沉积环境,有机碳含量高,页岩以纹层状结构为主,岩石组成脆性矿物含量高,含有大量的裂缝。可见,具有强还原沉积环境的页岩通常具有较好的勘探前景。

Shale oil and gas are currently attracting global oil and gas exploration and research interest, however, their potentialevaluation is considered as the main difficulty. The article examines four shale formation in China and North America including GreenRiver Formation lacustrine shale and Niobrara Formation inland marine shale in North America, Longmaxi Formation marine shale andJiyang 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 NorthAmerica were characterized trace elemental analysis, biomarker compounds, X-ray computed tomography(X-CT) and X-raydiffraction(XRD). Results show that the four formation shales have certain reducing sedimentary environment and highpaleoproductivity in Green River formation and Niobrara formation in North America, as well as Longmaxi Formation and shale inJiyang Depression. As the Niobrara formation shale has dysoxic-suboxic conditions, it has massive layers, lower fracture structure, thelowest organic content and reservoir volume in the four formation shales. The Longmaxi Formation shale is mainly composed ofsiliceous with high organic content, and the reservoir has more large pore and certain fracture structure, which can be attributed toanoxic 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.