川中震旦系灯影组多期流体充注及油气成藏的关键时期

Recently, a considerable progress has been made in the exploration of gas in the Sinian in the central Sichuan basin. Few conventional ways are available for determining the history and the key period of hydrocarbon accumulation in Sinian in the study area due to the complexity of its geological conditions, the multistage tectonic evolution, the outstanding fluid multistage charging characteristics, and its multistage oil and gas accumulation in the Sinian. In this project, from the micro-perspective,the charging and filling process of minerals and bitumen in bores, holes and cracks of reservoir are to be explored. For the determining of the geochemical characteristics of each phase fluid, the following methodology will be adopted: strontium stable isotopic analysis, carbon stable isotopic analysis and oxygen stable isotopic analysis and fluid inclusion analysis, trace element geochemical analysis and testing. In this project, the chronological analysis of the representative mineral and asphalt radioisotopes will be conducted: The results of the geochemical characteristics and chronological analysis of installments fluid will be used as the evidence for or against each other, so that we can define the movement characteristics and the time of the fluid. The findings of the fluid inclusions analysis will help to determine the key period of it's hydrocarbon accumulation and the age in which it was accumulated.

川中地区震旦系天然气勘探最近获得重大突破；但其地质条件复杂，震旦系经历了多期构造演化，流体多期充注特征明显，油气多期成藏，常规的油气成藏研究思路和方法难以厘定区内震旦系油气成藏历史和关键时期；本立项从微观的角度出发，拟对储层孔、洞、缝中矿物和沥青的充填次序进行研究，对其进行配套Sr、C、O稳定同位素、包裹体、微量元素的地球化学分析和测试，确定每期流体的地球化学特征。对代表性的矿物和沥青进行放射性同位素的年代学分析；将每期流体的地球化学特征和年代学分析结果相互印证和约束，限定各期流体活动的特征和时间，借助流体包裹体的分析结果，确定震旦系油气成藏的关键时期和成藏年代。

本研究以川中高石梯-磨溪地区震旦系灯影组储层岩石学特征研究为基础，通过储层中流体包裹体激光拉曼和孔、洞、缝充填物锶、碳、氧同位素分析，并据地层埋藏史及热演化史，分别恢复了震旦系灯影组和寒武系龙王庙组地层流体压力、流体系统、油气充注及油气成藏过程，建立了研究区震旦系和寒武系的油气成藏模式。本研究取得的主要成果如下：.(1)研究区震旦系灯影组储层中不同矿物充填分别对应了第一期盐水充注、第一期石油充注、第二期盐水充注及第二期油气充注及第三期天然气充注的多期流体充注过程。该矿物充填序列完整记录了震旦系成藏流体的演化过程和充注序列。.(2)震旦系灯影组储层孔、洞、缝中充填白云石、方解石及石英的Sr、C、O同位素测试分析结果表明下寒武统筇竹寺组烃源岩生油窗期，震旦系灯影组储层与下寒武统处于同一个连通且开放的流体系统之中；但生气窗期以后，震旦系灯影组与寒武系龙王庙组分属两个独立的流体系统并各自演化至今。.(3)恢复了研究区震旦系灯影组从古到今流体压力演化过程，震旦系灯影组古流体压力系数变化为1.0→1.1～1.2→1.2→1.2～1.3→1.0～1.1，表明震旦系灯影组作为区域岩溶孔洞型储集层在地史过程中始终未出现过超高压现象；寒武系龙王庙组古流体压力系数演化为1.0→2.1～2.2→1.8～1.9→1.6～1.8→1.55～1.75，表明滩相寒武系龙王庙组地层压力在地史过程中具有超高压或超压特征。. (4)研究区震旦系油气成藏演化从古到今经历了震旦系沉积后的地层抬升剥蚀阶段；寒武系沉积期的绵阳-长宁拉张槽发育至消亡阶段；三叠系沉积后古油藏形成阶段；侏罗系沉积后的早期古气藏形成阶段；白垩系沉积后的古油藏全部转化为气藏阶段以及现今的气藏调整局部富集成藏的过程。最后两个阶段为研究区震旦系从古气藏到今气藏油气成藏的关键时期。. (5)根据现今地层实测压力数据及岩性组合分析，川中高石梯-磨溪地区震旦系灯影组和寒武系龙王庙组气藏存在有效的多级压力和岩性封盖系统，为此，形成了保留至今的震旦系灯影组和寒武系龙王庙组整装大气田。