雪峰山西侧上奥陶统五峰组烃源岩特征及油气地质意义

雪峰山西侧处于四川盆地东南边缘与雪峰山构造带之间的过渡带， 目前对该区下古生界有效烃源岩的研究主要基于有限的地质及钻井资料，认识程度不高。为此，通过野外地质调查、样品采集及室内有机地球化学分析等方法，研究了该区上奥陶统五峰组烃源岩的分布规律及有机地球化学特征。结果表明：①五峰组沉积时黑色页岩具有向陆一侧迁移的特征，3个厚度较大的区域分别为石柱-南川-桐梓、鹤峰-咸丰-秀山、桃源-安化-靖州；②有机质含量较高的区域主要为石柱-南川-习水一线，与沉积厚度较大的地区基本一致；③有机显微组成、族组成、干酪根碳同位素、甾萜烷、芳烃标志物及Pr/Ph分析表明，五峰组黑色岩系沉积母质以菌藻类等低等浮游生物为主，沉积水体具有一定盐度，总体为较强的还原环境且各地水体深度有所差异；④等效镜质体反射率为1.37%～2.73%，H/C为0.52～0.65，大部分样品达到高成熟阶段。结论认为：该区奥陶系五峰组-志留系龙马溪组黑页岩有机质含量较高，大多未达过成熟阶段，页岩气资源潜力巨大，是目前中国南方页岩气勘探的有利区块之一。

Features and petroleum geologic significances of source rocks in the Upper Ordovician Wufeng Formation to the west of Xuefeng Mountain

The area to the west of the Xuefeng Mountain is a transitional zone between the southeastern margin of the Sichuan Basin and the Xuefeng structural zone. For lack of enough geologic and drilling data, we know little about the effective source rocks in this area. In view of this, based on field geologic survey, sampling and laboratory geochemical analysis, the distribution patterns and geochemical behaviors are first analyzed of the Upper Ordovician Wufeng Fm source rocks. The following conclusions are drawn. The black shales in the Wufeng Fm show features of landward migration, with greater thickness occurring in Shizhu Nanchuan Tongzi (A area), Hefeng Xianfeng Xiushan (B area), and Taoyuan Anhua Jingzhou (C area). High TOC mainly occurs along the Shizhu Nanchuan Xishui area, basically being consistent with the distribution of sediments with greater thickness. The analysis of microscopic organic composition, group composition, carbon isotope of kerogen, terpane, sterane, aromatic biomarkers and Pr/Ph indicate that the parent materials of the black shales in the Wufeng Fm are dominated by low planktons such as bacteria and algae and the sedimentary environment was a strong reducing one as a whole, with water bodies having certain salinity and variable depths. Equivalent vitrinite reflectance is 1.37% ~2.73% and H/C is 0.52 ~ 0.65. Most of the samples are highly mature. It is believed that the black shales in the Ordovician Wufeng Fm and Silurian Longmaxi Fm are high in TOC, mostly have not entered the over maturity stage, and have high shale gas potential, thus being one of the favorable exploration targets of shale gas in South China.