四川盆地五峰-龙马溪组页岩成熟度研究

上奥陶统五峰组-下志留统龙马溪组海相页岩是四川盆地下古生界主要的烃源岩和页岩气勘探目标，有机质成熟度不仅是油气生成评价的关键，也是页岩品质评价的重要指标之一.下古生界页岩有机质成熟度一直以来是有机岩石学研究的难点与热点问题.由于下古生界缺乏镜质体，先前的研究多是采用沥青反射率转换为等效镜质体反射率的方法，并且由于沥青的局限性和不确定性，使得五峰-龙马溪组页岩的成熟度缺乏统一的认识和系统研究.通过采集四川盆地及其周缘的岩心和露头样品，系统分析了页岩有机显微组分光学反射率特征.结果表明笔石和固体沥青是最主要的两类有机显微组分.根据固体沥青的显微结构形态和光性特征，将固体沥青大体上分为两类:（1）颗粒状-棱角状的充填在孔隙和微裂缝中高反射率焦沥青；（2）以细小不规则表面的有机质颗粒大量分散于粘土矿物基质中的低反射率基质固体沥青.焦沥青与笔石随机反射率均可以表征下古生界页岩有机质成熟度.但焦沥青反射率略低于笔石反射率，并且随着成熟度的增高，笔石反射率的增速大于焦沥青，各向异性也显著增强.相对于固体沥青反射率，笔石随机反射率分布更为集中，更适合作为含笔石页岩有机质成熟度指标.但是笔石反射率与等效镜质体反射率在过成熟阶段的换算关系需要进一步研究. 

Thermal Maturity of Wufeng-Longmaxi Shale in Sichuan Basin

The marine shale of Upper Ordovician Wufeng Formation (O₃w)-Lower Silurian Longmaxi Formation (S₁l) is the main source rock and the target of shale gas exploration in Sichuan Basin.Organic matter maturity is not only the key to evaluate hydrocarbon generation, but also a vital indicator of shale quality evaluation.The maturity of organic matter in Lower Paleozoic shale has always been a difficult and hot issue in organic petrology.However, the previous studies were focused on the conversion of solid bitumen reflectance to equivalent vitrinite reflectance on account of the lack of vitrinite in Lower Paleozoic stratum.And the limitation and uncertainty of bitumen give rise to a lack of uniform understanding and systematic research of Wufeng-Longmaxi shale on thermal maturity.The core and outcrop samples of Wufeng-Longmaxi shale were collected in Sichuan Basin and its periphery areas for optical analysis of organic matter.The macerals and optical characteristics of various organic matter in Wufeng-Longmaxi shale were analyzed.The main macerals organic components are composed of the graptolite fragments and solid bitumen.Two types of solid bitumen have been distinguished in shales, based on optical properties and microstructure characteristics in reflected light:(1) pyrobitumen—a highly reflecting granular and sharp angular bitumen accumulates in intergranular pore spaces and microfractures; (2) matrix solid bitumen—an irregular granular surface and finely organic matter particle widely disseminated in the clay mineral matrix with low reflectance.The random reflectance of pyrobitumen is slightly lower than that of graptolite in the same sample.The increase of graptolite reflectance is faster than that of solid bitumen with the increase of maturity, and anisotropy increases significantly.Both pyrobitumen and graptolite can be used for maturity analysis in Lower Paleozoic shale.Compared to the reflectance of solid bitumen, the random reflectance of graptolite is more suitable as maturity index due to reflectance value show a narrower range.However, its relationship with vitrinite reflectance at overmature stage still needs further study.