深层高-过成熟天然气藏来源、原位裂解成因判别及其古油藏充注途径示踪研究：以乐山-龙女寺古隆起为例

The objective of this study is to draw lessons from the domestic and foreign practical experience and relevant research results in the exploration and development of deep ancient uplift that have been discovered (such as central, northern ancient uplift of Tarim oilfield), and aimed at the facing problems in the deep oil and gas exploration of Leshan-Longnvsi palaeohigh in deep Sinian-Cambrian system of sichuan basin. This project will adopt new geological-geochemical technology, and study the genetic relationships between gas, asphalt and source rocks, identify oil cracking in situ of natural gas pool or oil cracking outside gas pool after oil migration in distance, trace ancient oil reservoir filling way and gas migration direction and make clear the ancient oil-gas reservoir accumulation periods and time, thus to explore the paleo oil and gas accumulation history and mechanisms for Leshan-Longnvsi ancient uplift, the ancient uplift hydrocarbon accumulation and evolution, and reveal the hydrocarbon source focal position and advantageous direction of future oil and gas exploration. Based on analysis of reservoir bitumen and light hydrocarbon, this research can explore new methods to trace filling way of ancient oil reservoir and technology to detect adsorbed light hydrocarbon using molecular sieve, determine some effective light hydrocarbon (adsorbed “heavy” hydrocarbon in natural gas) parameters for high-over mature gas and hydrocarbon source rocks, indicate the geochemical evolution of high-over mature marine oil and gas during the process of their accumulation, provide a reference for oil and gas exploration in deep marine basin, and also an important reference for resource potential assessment of high-over mature oil and gas under the background of complex tectonic activity with a long history.

本项目的研究旨在借鉴国内外已发现深层古隆起(如塔里木油田塔中、塔北古隆起）油气藏勘探、开发实践经验及相关研究成果基础上，针对四川盆地乐山-龙女寺古隆起深层震旦-寒武系深层油气勘探中面临的问题，采用地质-地球化学新技术，研究油-气-沥青-烃源岩的成因联系，判别天然气藏原位裂解-异位裂解成因，示踪古油藏充注与天然气调整运移的方向和途径，厘定古油藏-气藏成藏期次与时间，从而探索乐山-龙女寺古隆起油气成藏机理与演化历史，揭示该区烃源灶方位与有利的油气勘探方向。通过本项目研究，可以探索基于储层沥青的古油藏充注途径示踪技术和分子筛吸附轻烃检测技术，确定一些可进行高-过成熟天然气与烃源对比的轻烃（天然气中的吸附重烃）参数，指明高-过成熟海相油气在成藏过程中的地球化学演变，为深层海相盆地油气勘探提供参考或依据，也为复杂构造背景下高-过成熟油气资源潜力的评价提供重要借鉴。

深层一些古老地层由于现今演化程度很高，古油藏中的原油几乎都已裂解为储层固体沥青和天然气，天然气干燥系数大，组份单一，所包含的可用于气-源对比的信息极少，使得常规的气源对比以及油运移示踪及成藏机理研究带来很大困难。因此，对于高-过成熟的深层油气藏而言，迫切需要探索出新的技术方法来进行油气源对比和油气充注示踪研究。. 本文综合利用储层固体沥青的分子生物标志物、碳同位素和微量-稀有元素等先进检测方法和油藏地球化学原理等地质-地球化学理论，开展了高石梯和磨溪地区储层沥青的地球化学特征分析、储层沥青-烃源岩地球化学对比和古油藏充注方向示踪研究。.本文的主要结论是：.1、预测了储层沥青成熟度（1.75%-2.82%）、沥青对应储层的“视成熟度”（2.08%-4.0%）和天然气“成熟度”（1.34%-1.95%）分布，确定出该区灯影组和龙王庙组储层沥青为古油藏原位裂解成因。.2、确定出高石梯-磨溪地区的储层沥青属于同一族群，这些沥青的母质来源于还原性的海相页岩，其油源可确定为高石梯-磨溪地区的筇竹寺组和灯影组两套烃源层的共同贡献。.3、揭示出了震旦系灯二段、灯四段和下寒武统龙王庙组古油藏充注途径和特征：1）灯四段和灯二段高石梯地区古油藏充注更为强烈，而龙王庙组在磨溪地区古油藏充注更为强烈；2）龙王庙组除了从西向东充注方向外，从北向南的充注能力也比较强。.4、明确了烃源灶方位主要位于高石梯-磨溪地区以西的克拉通凹陷，在高石梯-磨溪地区以北也存在烃源灶。. 四川盆地乐山-龙女寺古隆起震旦系-下寒武统是国内外典型的高-过成熟原油裂解型天然气田。相关的成藏规律研究对探索和揭示大型古隆起海相油气田形成与富集规律具有重要理论价值。