四川盆地岳池–丰都地区下志留统龙马溪组生烃史研究

Research on the Hydrocarbon Generation History of the Lower Silurian Longmaxi Formation in Yuechi-Fengdu Area, Sichuan Basin

摘要: 下志留统龙马溪组烃源岩是四川盆地岳池–丰都地区志留系–石炭系含气系统的主力烃源岩，但其成熟度演化及生烃过程的研究十分薄弱，制约着该区域石炭系天然气成藏过程的研究。本文以构造–热历史为约束，结合烃源岩地球化学参数，利用盆地模拟技术对龙马溪组烃源岩进行成熟度史及生烃史模拟。结果表明，四川盆地岳池–丰都地区龙马溪组烃源岩总体上经历了三期成熟度增加阶段，分别为早志留世早期–晚志留世末期、早二叠世早期–早二叠世末期和早三叠世末期–早侏罗世末期；两期快速生烃阶段：早二叠世早期–早二叠世末期、早三叠世末期–早侏罗世末期。岳池–丰都地区龙马溪组烃源岩的生烃中心位于东南部，最大生烃强度达到100 × 10⁸ m³/km²，生烃中心生成的大量油气可以有效地向石炭系的古构造高部位运移，并在圈闭中聚集，形成古油藏。本研究成果可以为岳池–丰都地区志留系–石炭系天然气的勘探提供重要依据，下一步勘探应着眼于在东南部生烃中心及其周缘的优质储层中寻找大中型规模的天然气气藏。

Abstract: The Lower Silurian Longmaxi Formation is the main source rock of the Silurian-Carboniferous gas bearing system in the Yuechi-Fengdu area of the Sichuan Basin. However, the research on its maturity evolution and hydrocarbon generation history is very weak, which restricts the study of the natural gas accumulation process of the Carboniferous in this area. This article takes the tectono-thermal history as a constraint, combines it with the geochemical parameters of the source rock, and uses basin modeling technology to simulate the maturity evolution and hydrocarbon generation history of the Longmaxi Formation. The results show that the source rock of the Longmaxi Formation in the Yuechi-Fengdu area of the Sichuan Basin experienced three stages of increasing maturity, which are the Early stage of the Early Silurian-the end of the Late Silurian, the Early stage of the Early Permian-the end of the Early Permian, and the end of the Early Triassic-the end of the Early Jurassic. Two stages of rapid hydrocarbon generation are the early stage of the Early Permian-the end of the Early Permian and the end of the Early Triassic-the end of the Early Jurassic. The hydrocarbon generation center of the Longmaxi Formation in the Yuechi-Fengdu area is located in the southeast, with a maximum hydrocarbon generation intensity of 100 × 10⁸ m³/km². A large amount of oil and gas generated by the hydrocarbon generation center can effectively migrate to the high parts of the Carboniferous paleo-structures and accumulate in traps, forming paleo-oil reservoirs. The results of this study can provide essential basis for the exploration of Silurian-Carboniferous natural gas in the Yuechi-Fengdu area. The next exploration should focus on finding large and medium-sized natural gas reservoirs in the high-quality reservoirs around the southeastern hydrocarbon generation center and its surroundings.