Abstract: The Sinian-Cambrian ancient shale gas reservoirs represent a key field for current hydrocarbon exploration and development. However, owing to their prolonged burial history, high thermal maturity, and the superimposition of multiple tectono-thermal events, the research on shale hydrocarbon generation and evolution as well as gas accumulation processes faces significant challenges. This study targets at the Sinian-Cambrian shales in western Hubei area. The combination of multiple paleothermometers, including low-temperature thermochronology and bitumen reflectance, enables the restoration of the thermal evolution history in western Hubei area since the Paleozoic, and reconstructed the burial and hydrocarbon generation processes of Sinian-Cambrian shale in typical wells. Based on this, in combination with fluid inclusion analyses, the time, temperature, and maturity conditions for shale oil-gas generation are determined, providing key evidence for reconstructing the shale gas accumulation process. The results indicate that during the Early Paleozoic burial stage, the Huangling paleo-uplift experienced a relatively shallow burial depth (approximately 2 500 m)where the shale had a low degree of thermal evolution, thereby preserving its hydrocarbon generation potential. In contrast, the western Hunan-Hubei depression reached greater burial depths (approximately 5 000 m)during the same period, where the shale underwent a high level of thermal evolution and rapid peaks of oil-gas generation during the Late Ordovician to Early Silurian, resulting in an early loss of hydrocarbon generation capacity and a subsequent transition into the preservation stage. Fluid inclusion analyses reveal that the Sinian Doushantuo Formation shale in Huangling paleo-uplift experienced three evolutionary stages, i.e., an oil-generation peak with substantial oil production during Early Permian, a gas-generation peak accompanied by large-scale cracking of liquid hydrocarbons into gaseous hydrocarbons in Triassic, and shale gas dissipation during Early Cretaceous. In contrast, the Cambrian Niutitang Formation shale recorded two stages, including a gas-generation peak in Triassic and shale gas dissipation in Early Cretaceous.

Key words: hydrocarbon generation and evolution, low-temperature thermochronology, fluid inclusion, Sinian-Cambrian shales, western Hubei area

摘要： 震旦系—寒武系古老页岩气藏是当前页岩气勘探开发的重要领域,但由于其埋藏历史漫长、成熟度高且经历多期构造-热事件叠加,页岩的生烃演化与成藏过程研究面临着显著挑战。以鄂西地区震旦系—寒武系页岩为研究对象,综合运用低温热年代学和沥青反射率等多种古温标,恢复了鄂西地区古生代以来的热演化史,重建了典型钻井内震旦系—寒武系页岩的埋藏—生烃演化过程。在此基础上,结合流体包裹体分析,明确了页岩生油与成气过程的时间、温度和成熟度条件,为页岩气成藏过程的重建提供了关键依据。研究结果表明,黄陵隆起区在早古生代埋藏阶段的埋深较小(约为2 500 m),其页岩的热演化程度较低,生烃潜力得以有效保存,而湘鄂西坳陷区在同期的埋深较大(约为5 000 m),其页岩的热演化程度高,并在晚奥陶世—早志留世快速经历了生油与生气高峰,过早丧失了生烃能力并转入保存状态。流体包裹体揭示黄陵隆起区的震旦系陡山沱组页岩经历了3个生烃演化阶段:早二叠世达到生油高峰并大量生油,三叠纪进入生气高峰并伴随液态烃大量裂解为气态烃,以及早白垩世发生页岩气散失;寒武系牛蹄塘组页岩记录了2个生烃演化阶段:三叠纪进入生气高峰和早白垩世发生页岩气散失。

关键词: 生烃演化, 低温热年代学, 流体包裹体, 震旦系—寒武系页岩, 鄂西地区