四川盆地富有机质页岩硅质生物成因及对页岩气开发的意义

通过岩石学、有机碳含量、主量元素和力学性质分析, 对四川盆地长宁双河剖面上奥陶统五峰组和下志留统龙马溪组页岩进行硅质成因研究。长宁双河剖面底部页岩过量硅含量为40%~62.7%, 具有高SiO₂, P₂O₅和Fe₂O₃, 低Al₂O₃, TiO₂, FeO和MgO的特征。Al/(Fe+Al+Mn)比值为0.67~0.71, Si/(Si+Al+Fe)比值为0.89~0.93, 在Al?Fe?Mn图解上落在生物成因区。五峰组有机碳含量(TOC)为2%~7.55%, 平均3.73%。龙马溪组页岩有机碳含量为0.23%~8.36%, 平均1.16%, TOC>2%段集中在剖面底部21 m, TOC与硅质含量具有正相关关系。页岩中发现大量放射虫、海绵骨针等微体化石, 证实硅质为生物成因, 指示页岩沉积环境为深水陆棚, 有利于形成自然裂缝和后期压裂改造, 对页岩气勘探开发具有重要意义。

Biogenic Silica of Organic-Rich Shale in Sichuan Basin and Its Significance for Shale Gas

Through analysis of shale petrology, TOC, major elements and physical mechanism, this paper studies on silicon genesis of upper Odorvision Wufeng Formation and lower Silurian Longmaxi Formation in Changning- Shuanghe profile of Sichuan Basin. The results indicate that up to 40%?62.7% SiO₂ in lower part of the profile is excess. They are characterized by high SiO₂, P₂O₅, Fe₂O₃ and low Al₂O₃, TiO₂, FeO, MgO content. Al/(Fe+Al+Mn) varies between 0.67?0.71, and Si/(Si+Al+Fe) between 0.89?0.93. In Al-Fe-Mn diagram, they are in biogenic area. TOC of Wufeng Formation is 2%?7.55%, average 3.73% and 0.23%?8.36%, average 1.16% for Longmaxi Formation. Segment of TOC > 2% mainly concentrated in the lower part, with thickness of 21 m. TOC and siliceous content have good positive correlation. Under the microscope, there are a lot of microfossils, such as radiolarians, sponge spicules, indicating the biogenic silica. Biogenic silica indicates sedimentary environment of deep shelf and is conducive to the formation of natural fractures and fracturing treatment, which is of great significance for shale gas exploration and development.