四川盆地页岩气地球化学特征及资源潜力

页岩气是绿色低碳清洁的非常规天然气资源。我国页岩气资源丰富，加快页岩气勘探开发，对于改善中国能源结构、实现中国“2030年碳达峰、2060年碳中和”目标具有重要现实意义。四川盆地奥陶系五峰组—志留系龙马溪组是当前中国页岩气勘探开发的重点层系。通过对四川盆地威远、长宁、昭通、涪陵及威荣等地区五峰组—龙马溪组页岩气实验分析，系统分析了五峰组—龙马溪组页岩气地球化学特征，探讨了页岩气成因、碳氢同位素倒转原因及页岩气来源，展望了盆地页岩气资源勘探前景。结果表明：①五峰组—龙马溪组页岩气为典型干气，碳氢同位素均呈负序列分布，长宁、昭通与涪陵地区烷烃气碳同位素组成相对威远、威荣地区更重、具有更高热演化程度，稀有气体为典型壳源成因。②五峰组—龙马溪组页岩气为高—过成熟阶段热成因油型气，主要为原油裂解气和干酪根裂解气的混合气，烷烃气碳氢同位素倒转主要由高—过成熟阶段原油裂解气与干酪根裂解气的混合、高演化阶段地层水与甲烷交换作用等原因造成。③五峰组—龙马溪组页岩气的甲烷碳同位素值与下志留统龙马溪组泥岩干酪根碳同位素值较为匹配，符合碳同位素分馏规律δ¹³C_干酪根>δ¹³C_油>δ¹³C_烷烃气。④四川盆地海相、海陆过渡相和陆相页岩气资源总量约为41. 5×10¹² m³，资源前景广阔。

Geochemical characteristics and resource potential of shale gas in Sichuan Basin

Shale gas is a green， low-carbon and clean unconventional natural gas energy. China is rich in shale gas resources. Accelerating shale gas exploration and development is of great practical significance to improve China's energy structure and achieve the goal of “2030 carbon peak neutralization and 2060 carbon neutralization”. The Ordovician Wufeng Formation to Silurian Longmaxi Formation in Sichuan Basin is the key strata for shale gas exploration and development in China. Based on the experimental analysis of shale gas in Wufeng Formation to Longmaxi Formation in Weiyuan， Changning， Zhaotong， Fuling and Weirong areas of Sichuan Basin， this paper systematically analyzes the geochemical characteristics of shale gas in Wufeng Formation to Longmaxi Formation， discusses the genesis of shale gas， the causes of hydrocarbon isotope inversion and the source of shale gas， and looks forward to the exploration prospects of shale gas resources in the basin. It has important guiding significances for shale gas exploration and development in Sichuan Basin and even in China. The results show that： （1） The shale gas from Wufeng Formation to Longmaxi Formation is a typical dry gas， and the hydrocarbon isotopes are distributed in negative sequence. The carbon isotopes of alkane gas in Changning， Zhaotong and Fuling areas are heavier and have a higher degree of thermal evolution than those in Weiyuan and Weirong areas， and the rare gas is of crustal origin. （2） Shale gas from Wufeng Formation to Longmaxi Formation is a thermogenic oil type gas at high-over mature stage， which is mainly the mixture of crude oil cracking gas and kerogen cracking gas. The hydrocarbon isotope inversion of alkane gas is mainly caused by the mixing of crude oil cracking gas and kerogen cracking gas at high-over mature stage， the exchange between formation water and methane at high evolution stage and so on. （3） The carbon isotopic values of methane in shale gas from Wufeng Formation to Longmaxi Formation match the carbon isotopic values of kerogen in mudstone of Longmaxi Formation of Lower Silurian， which conforms to the law of carbon isotopic fractionation δ¹³C_kerogen>δ¹³C_oil>δ¹³C_{alkane gas}. （4） The total amount of marine， marine continental transitional and continental facies shale gas resources in Sichuan Basin is about 41.5×10¹² m³， with broad exploration prospects in resource potential.