川中震旦系灯影组古水溶气藏的证据及成藏贡献

Natural gas accumulation of Sinian in Sichuan Basin has undergone multi-stages and multi-periods of evolution. Since the Late Cretaceous, the uplift process lead to re-adjusting and positioning the gas pools, and the process of hydrocarbon accumulation is complicated.Therefore, the large exploration breakthrough has not been obtained. The recent discovery of Well Gaoshi 1 in the Sinian confirmed that the Sinian still has a broad exploration prospects. The Sinian cores recorded six fluid charging events, which the fifth charging is the key events of natural gas accumulation of the Sinian reservoir -formation of water soluble methane inclusions, indicates that Sinian had existed ancient water-soluble gas reservoir. The paleo water-soluble gas reservoir of fifth fluid filling formed is the latest fluid phase evolution in the Sinian reservoir，but also the nearset geological event away from the present gas pools finally positioned, which is most closely related to the relationship of the present gas. The water-soluble gas released from formation water resulted from uplift process since the Late Cretaceous in Sichuan Basin. It may be the main accumulation mechanism of the Sinian gas reservoir which has not been found. The formation of Urengoy gas field, Kela 2 gas field, Hetianhe gas field related with water-soluble releasing from formation water as well. In this study, the key accumulation event of Sichuan Sinian - formation of the ancient water-soluble gas reservoir as a starting point to study the evidence of its formation, the formation period, the desolution process and its contribution to hydrocarbon accumulation, and provide a reference for the hydrocarbon exploration in the Sinian gas pools.

四川盆地震旦系天然气成藏经历了多期多阶段演化，晚白垩世以来的隆升作用又导致气藏重新调整和定位，成藏过程复杂，因而一直未能获得大的勘探突破。近期川中震旦系工业气井-高石1井的发现证实震旦系仍具有广阔的勘探前景。震旦系岩心中记录了6期流体充注事件，其中第五期流体充注为震旦系成藏的关键事件- - 水溶态甲烷包裹体的形成，指示震旦系曾经存在古水溶气藏。第五期流体充注所形成的古水溶气藏是震旦系油气藏流体相态演化的最后一幕，也是距现今气藏最终定位和定型最近的地史时期，和现今气藏的关系最为密切。而四川盆地晚白垩世以来的隆升过程导致的水溶气脱溶可能是威远气田和盆地内还未发现的震旦系气藏的主要成藏机制。乌连戈依气田、克拉2气田、和田河等气田的形成也和水溶气的脱溶有关。本研究以川中地区震旦系关键成藏事件-古水溶气藏的形成为出发点，研究其形成的证据、形成时间以及脱溶过程的成藏贡献，为震旦系油气勘探提供借鉴。

四川盆地川中安岳构造震旦系灯影组气藏为近年来盆地内重大的勘探发现。安岳构造震旦系经历了多期的构造演化和油气成藏过程，这一过程被白云岩储层及孔、洞、缝中充填的不同世代矿物中的流体包裹体所记录。我们对晚期充填的石英或方解石矿物中的烃类包裹体进行了激光拉曼分析，认为其是液态甲烷包裹体。并进一步对其进行了冷冻加热实验，通过冷冻加热实验过程中的相态变化确认其为液态甲烷包裹体，说明古气藏曾经为水溶气藏。包裹体的均一温度和所计算的捕获压力表明，液态甲烷包裹体是在高温高压的条件下捕获的，并以此估算了地层水对天然气的溶解能力。根据震旦系灯影组储层中所沉淀矿物的先后次序关系，我们在灯影组白云岩储层中共识别出了6期流体充注，所研究的液态甲烷包裹体赋存在最晚期沉淀的第五世代矿物中。该期矿物的沉淀和结晶发生在晚期的深埋—隆升之前的地质过程中，之后由于喜马拉雅期的构造运动导致川中地区普遍遭受隆升剥蚀，灯影组减压降温，古水溶气藏中的天然气从地层水中脱溶，形成现今的常规天然气藏。. 本项目的工作对经历过多期构造演化的复杂叠合盆地油气成藏过程的研究进行了探索，尝试从矿物的充填序列分析流体的充注过程，以地球化学的手段揭示各期流体充注的特征，分析流体的相态、温度压力条件等，揭示其石油地质含义。项目的研究方法和认识为四川盆地震旦系-下古生界的油气成藏研究提供了借鉴。