川中地区深层震旦系-寒武系流体压力演化和油气多期成藏研究

After more than 50 years of oil and gas exploration, the deep formation of Sinian-Cambrian System in Central Sichuan Basin have achieved a great success. especially, Longwangmiao Formation of Cambrian System which has discovered the biggest marine carbonate gas field in China. This significant discovery confirms the petroleum potential of this basin. Sichuan Basin is a typical superimposed basin, because of multi-stage basin formation, with a variety of different source rock types, accompanied by different phases/stages of hydrocarbon migration and accumulation. Sinian-Cambrian System has experienced a series of maturation forming oil accumulations in the paleo-oil-reservoirs and underwent thermal cracking to form pale-gas-reservoirs that form the present day gas-reservoirs. This complexity in processes have caused evolution of fluid pressure system within the reservoir units. This research project entails a deep study of the Sinian-Cambrian system of Central Sichuan Basin based on the geological, seismic, wirelogs, core and geochemical date sets. The periods and time of hydrocarbon accumulation and migration has been determined in this study using basin-modelling, fluid inclusion analysis and asphalt Re-Os isotopic dating techniques. The measured datum of present pressure was integrated with inclusions, PVT simulation method and methane inclusions dynamics simulation method by which we can restore the fluid pressure characteristics of every accumulation at specific period. At last, we clarify the dynamic process of hydrocarbon accumulation, comparing the similarities and differences between Sinian and Cambrian system. This project will serve as a guide in the hydrocarbon exploration of the Lower Paleozoic Formation of Sichuan Basin. It will further improve on the theory of the Lower Paleozoic hydrocarbon accumulation.

川中地区深层震旦系-寒武系在经过了50余年的油气勘探后，磨溪区块寒武系龙王庙组中发现了目前我国单体规模最大的特大型海相碳酸盐岩整装气藏，再次证实了该层系可观的勘探潜力。四川盆地是一个典型的叠合盆地，在多期成盆、多源多灶、多期成藏和多期调整下，震旦系-寒武系油气先后经历了古油藏形成→古油藏裂解成古气藏→古气藏调整为现今气藏这一系列成藏过程，造成流体压力系统也经过了复杂的演化｡本项目以川中地区深层震旦系-寒武系为研究对象，基于地质、地震、钻井、测井及地化等资料，应用盆地数值模拟、流体包裹体分析测试和沥青Re-Os同位素定年技术，确定油气成藏期次和时间，以现今实测压力为基础，利用包裹体PVT模拟法和甲烷包裹体热动力学模拟法，恢复各成藏期的流体压力特征，在此基础上阐明油气成藏动态过程，并比较震旦系和寒武系油气成藏的异同性。本项目对于丰富我国下古生界油气成藏理论和指导勘探油气新区都具有一定的价值。

四川盆地是中国南方最大的含油气叠合盆地，深层碳酸盐岩蕴藏着大量的天然气资源。研究川中高石梯-磨溪构造震旦系-下寒武统的油气成藏过程，对于加深四川盆地深层油气成藏研究、丰富我国下古生界油气成藏理论和指导勘探油气新区都具有重要意义。基于研究区构造背景和油气成藏条件，应用流体包裹体分析测试方法，结合盆地数值模拟技术，确定油气成藏期次和时间，分析流体压力演化特征，进而恢复川中高石梯-磨溪构造震旦系灯影组-下寒武统龙王庙组油气成藏过程。.灯影组和龙王庙组储层中都分别存在至少三期流体充注，从孔洞边缘向中心依次可见晶粒状白云石-沥青-石英（白云石/方解石），分别充注于生油窗前，生油窗期和生气窗后。储层中则检测到一期发黄-黄绿色荧光的纯液烃包裹体、一期发蓝色荧光的气液烃包裹体和一期不发荧光的纯气烃包裹体。.基于流体包裹体分析测试的结果，高石梯-磨溪构造震旦系灯影组-寒武系龙王庙组共经历过三期油气成藏：第一期大量生油并形成古油藏的阶段，成藏时间为219～194Ma，即中三叠世-早侏罗世；第二期为原油部分裂解生成天然气的阶段，成藏时间为192～146Ma，即侏罗纪；第三期为原油大量裂解，古气藏形成并经过后期改造的过程，成藏时间为168～0Ma，即中-晚侏罗世至今。古油藏形成时，灯影组和龙王庙组为弱超压系统；古油藏裂解形成古气藏的过程中，二者均表现出弱超压-超压的特征；古气藏形成以后的早期改造过程中，超压幅度并未受到大的影响；后期受强烈隆升作用影响，灯影组气藏运移到威远构造并逸散，地层压力从强超压迅速下降至常压，而龙王庙组古气藏超压幅度略有下降并保存至今。.将高石梯-磨溪构造灯影组油气成藏模式归纳为新生古储、古生新储近源多期成藏-天然气长距离侧向强调整-微开放常压系统，龙王庙组油气成藏模式归纳为古生新储远源多期成藏-天然气近距离弱调整-封闭高压系统。