The Penglai area is an emerging giant gas field in the Sichuan Basin supporting the carbon neutrality goal. To accelerate the exploration, this study combines petrographic observations using optical and cold cathodoluminescence microscopy, fluid inclusion microthermometry, Raman spectroscopy, 1D basin modeling and fluid inclusion PVTX modeling techniques to reveal the paleo-fluid P-T evolution in the second member of the Dengying Formation (Ediacaran age). The results firstly showed a diagenetic sequence which includes three phases of dolomite (1–3), bitumen, quartz (core and overgrowth) and fluorite. Then, ten paleo-fluid episodes were identified based on microthermometric histograms of different mineral phases. Finally, by integrating the Raman results, the hydrostatic and lithostatic gradients calculated by the constructed 1D basin model, and the existing equation of states, the homogenization pressure of fluid inclusions from each fluid episode was determined. By assuming the system was saturated by CH as suggested by Raman results, the homogenization pressure equals to the trapping pressure. The P-T trajectory indicates that the second member of the Dengying Formation experienced two sever pressure accumulation stages. One is between fluid episode #3 and #4 recorded by dolomite 3, due to oil generation, and the other is from fluid episode #5 in dolomite 3 to episode #7 in quartz overgrowth to episode #8 in fluorite due to oil cracking to gas. Also, two pressure releasing periods were recorded by fluid episode #5 in dolomite 3 and #9 and #10 in fluorite, caused by both basin uplifting and fluid pressure reaching the lithostatic pressure. This study provides insights into fluid pressure evolution in deeply buried carbonate reservoirs. The understandings can support further geoenergy utilization and reduce exploration risks.

中文翻译：

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川中北坡（蓬莱地区）埃迪卡拉系碳酸盐岩成岩作用及压力演化

蓬莱地区是四川盆地新兴的巨型气田，支撑着碳中和目标。为了加速勘探，本研究结合光学和冷阴极发光显微镜、流体包裹体显微测温、拉曼光谱、一维盆地建模和流体包裹体PVTX建模技术的岩相观测，揭示了灯影组古流体PT演化。埃迪卡拉纪）。结果首先显示了一个成岩序列，包括白云石（1-3）、沥青、石英（核心和增生）和萤石三个阶段。然后，根据不同矿物相的显微测温直方图确定了十个古流体事件。最后，通过综合拉曼结果、构建的一维盆地模型计算的静水力和岩性梯度以及现有的状态方程，确定了每个流体期的流体包裹体的均一压力。假设系统如拉曼结果所示被 CH 饱和，则均质压力等于捕集压力。 PT轨迹表明灯二段经历了两个严重的压力聚集阶段。一个是由于石油生成，白云石 3 记录的流体阶段 #3 和 #4 之间，另一个是由于石油裂解，从白云石 3 中的流体阶段 #5 到石英过度生长的阶段 #7 到萤石中的阶段 #8气体。此外，白云岩 3 中的#5 流体事件以及萤石中的 #9 和 #10 流体事件记录了两个压力释放期，这是由盆地抬升和流体压力达到岩石静压引起的。这项研究提供了对深埋碳酸盐岩储层流体压力演化的见解。这些谅解可以支持进一步利用地能并降低勘探风险。