四川盆地ZQ8井五峰组-龙一段有机质富集机制研究

四川盆地五峰组-龙一段黑色页岩为一套厚度稳定、有机质丰度高的优质海相烃源岩，是页岩气勘探开采的重要层系。为了解五峰组-龙一段有机质富集机制，对四川盆地川南低陡褶带南缘的ZQ8井进行了岩心、岩石薄片、X-衍射、扫描电镜、有机碳、有机碳同位素及微量元素分析。氧化还原指标（Ni/Co、V/Cr、U/Th）表明五峰组海水氧化还原条件由早期富氧氧化条件过渡到缺氧还原条件，龙一₁¹-龙一₁³小层为缺氧-贫氧还原环境，龙一₁⁴-龙一₂⁴小层为富氧氧化环境。氧化还原指标、生产力、笔石、矿物组分和TOC含量的相关性，证明缺氧或贫氧的还原性水体环境是有机质富集的主控因素，笔石、生物成因石英和黄铁矿促进有机质的富集，黏土矿物抑制有机质的富集。综合分析表明：五峰组富有机质页岩主要由火山作用带来大量的营养物质及温暖湿润气候条件下，笔石及浮游动植物繁殖，生产力高，在强滞留缺氧环境下形成；五峰组后期富有机质页岩主要由于冰川作用造成的大量生物灭绝，提供大量有机物质，在缺氧硫化环境下保存形成；龙马溪组富有机质页岩主要受极地冰川溶解，带来丰富的营养物质，生产力水平升高，在高水位海域形成的底部静海相缺氧环境下形成。

Organic matter enrichment mechanism in Wufeng Formations to Longyi member: A case study from ZQ8 well in Sichuan Basin

The black shale of Wufeng Formation to Longyi member in Sichuan Basin is a set of high-quality marine source rocks with stable thickness and high organic matter abundance. It is an important layer series for shale gas exploration and production. In order to understand the enrichment mechanism of organic matter in Wufeng Formation to Longyi member, the core, rock thin section, X-diffraction, scanning electron microscope, organic carbon, organic carbon isotopes and trace elements of ZQ8 well in the southern edge of low and steep fold belt in southern Sichuan Basin were analyzed. The redox indexes(Ni/Co, V/Cr, U/Th)show that the redox conditions of seawater in Wufeng Formation transition from early oxygen enriched oxidation conditions to anoxic reduction conditions. The anoxic oxygen environment deficient reduction of Longyi11-Longyi13 sublayer and the oxygen enriched oxidation environment of Longyi14-Longyi24 sublayer. The correlation between redox index, productivity, graptolite, mineral composition and TOC content proves that the reducing water environment with hypoxia or oxygen deficiency is the main controlling factor for the enrichment of organic matter. Graptolite, biogenic quartz and pyrite promote the enrichment of organic matter, and clay minerals inhibit the enrichment of organic matter. The comprehensive analysis shows that the organic rich shale of Wufeng Formation is mainly formed in the strong retention anoxic environment due to the large amount of nutrients brought by volcanism and the reproduction of graptolites and phytoplankton under warm and humid climate; in the later stage of Wufeng Formation, the organic rich shale was mainly caused by the extinction of a large number of organisms caused by glaciation, which provided a large amount of organic matter and was preserved in the anoxic sulfide environment; the organic rich shale of Longmaxi Formation is mainly dissolved by polar glaciers, bringing rich nutrients and increasing productivity. It is formed under the anoxic environment of static sea facies at the bottom of high water level sea area.