桂中坳陷早石炭世泥页岩地球化学特征及近源气成藏模式
Geochemical Characteristics of the Early Carboniferous Shale in Guizhong Depression and Their Contribution to Adjacent Gas Reservoirs

目前针对桂中坳陷早石炭世富有机质泥页岩的生烃潜力方面研究很少，严重制约了该区以页岩气为主的非常规油气勘探.本研究对鹿寨县城西石炭系鹿寨组泥页岩系统取样分析，从有机碳含量、岩石热解、有机碳同位素组成、抽提物正构烷烃组成特征及泥岩镜质体反射率多个方面讨论了该套泥页岩的生烃潜力；结合区域构造演化史总结了与下石炭统岩关阶泥页岩密切相关的3种近源气藏赋存模式.研究结果表明：泥页岩的TOC值分布于0.25%～15.67%，其中强制海退前沉积的泥页岩富含有机质，TOC值均大于2%，TOC值与氯仿沥青“A”、生烃潜量及总烃呈弱正相关关系.泥页岩的有机质类型主体为Ⅱ型；泥页岩的Ro值分布于1.72%～2.78%，处于过成熟阶段.泥页岩上下岩性组合特征及桂中坳陷现今所处的构造位置表明，坳陷中部对冲构造区为有利的近源气藏形成区，背冲构造区为较差区；坳陷边缘逆冲推覆构造区为存在岩性圈闭的近源气藏形成区.
To date there are only a few studies on genetic potential of the Early Carboniferous shale in Guizhong depression, which severely restricts the unconventional oil and gas exploration (mainly shale gas) in this area. In this study, typical profile measurements and sampling analysis of the shale from the Early Carboniferous slope facies in Guizhong depression were conducted, and then the hydrocarbon generating potential of the shale was discussed from multiple perspectives, including the TOC content, rock pyrolysis, organic carbon isotope composition,n-alkane composition and the vitrinite reflectance of the shale. Combined with regional tectonic evolution history, three models of near source gas reservoirs, which are closely related to the shale from the Lower Carboniferous Yanguanian Stage, are summarized. The results show that, TOC values are ranging from 0.25% to 15.67%. The shales deposited before forced regressive are rich in organic matter, with TOC values greater than 2%. There are weak positive correlations between TOC value and chloroform bitumen “A”, the hydrocarbon generating potential and the total hydrocarbon respectively. The type of the organic metter in the shales is mainly classified as kerogen type Ⅱ. The values of Ro are ranging from 1.72% to 2.78%, in the overmature stage. According to the lithologic characteristics and the present tectonic position of Guizhong depression, we suggest that the ramp structure zone in the middle of the depression is favorable for the formation of near source gas reservoirs, while the back thrust zone is poor. The thrust nappe structure zone in the edge of the depression is the near source gas accumulation zone with lithologic traps