海相油气成藏定年技术及其对元坝气田长兴组天然气成藏年代的反演
Key Dating Methods of Reservoir Accumulation in Marine Strata and Their Applications to Natural Gas of the Changxing Formation in Yuanba Gas Field

我国海相叠合盆地的油气特征及成藏过程表现出很强的复杂性，确定油气成藏年代极其困难，建立有效的确定成藏定年技术显得尤为迫切.为此基于稀有气体He年代积累效应和油气藏保存机制，建立了油气藏4He成藏定年地质模型及年龄估算公式，明确其为油气成藏定型时间；基于天然气40Ar/36Ar比值与源岩钾丰度及地质时代的关系，建立了追溯油气源岩时代的Ar同位素估算模型.磷灰石、锆石(U-Th)/He定年体系的封闭温度与含油气盆地生油气窗的温度范围较为一致，磷灰石、锆石(U-Th)/He年龄可以揭示含油气盆地抬升剥蚀时间、由构造抬升导致的油气藏调整时间，建立了固体沥青、原油中沥青质提取、溶样、Re-Os纯化富集及分离等Re-Os同位素测年前处理技术，可以直接确定固体沥青、原油等形成时间.按照含油气系统成藏地质要素形成时间或发生时间先后顺序，提出了从确定源岩形成－油气生成－运移充注－调整改造－成藏定型等成藏过程的定年技术序列.开展四川盆地元坝气田源岩时代、生排烃、运移充注、调整改造及成藏定型等关键过程的时间节点综合研究，明确了元坝气田的主力气源为上二叠统龙潭组烃源岩，两期原油充注时间分别为220～175 Ma、168～140 Ma；油裂解气发生在140～118 Ma，元坝地区约97 Ma以来发生构造抬升，尤其15 Ma以来气－水界面发生调整，约在12～8 Ma气藏最终定型并形成现今的气藏格局.
Petroleum characteristics and accumulation of the marine superimposed basins show strong complexity, which makes it difficult to determine key time of reservoir accumulation. It is urgent to establish effective dating methods for hydrocarbon source age, hydrocarbon generation and expulsion time, reservoir adjustment and stabilization time. On the basis of helium age accumulation effect and reservoir preservation mechanism, the helium dating model and age estimating formulas are put forward to determine the time of reservoir formation and stabilization retention after large scale of petroleum charging in this paper. According to the relationships between the 40Ar/36Ar ratio of natural gas, potassium abundance of source rock and the geological time, argon isotopic estimation model on the source rock age is fitting by many parameters. Based on the closure temperature on U-Th/He dating system of apatite and zircon being consistent with the temperature scope of hydrocarbon generation in sedimentary basin, uplift time and reservoir transformation time induced by tectonic uplift are revealed by means of time and closure temperature difference of close system in apatite and zircon, and geothermal gradient of sedimentary basin. By means of a series of condition test, pretreatment techniques including asphaltene extraction, acid dissolving, rhenium-osmium purity, enrichment and separation are established. Re-Os isotopic dating can be used to directly date hydrocarbon source rock, solid bitumen, oil and oil sand and offers hydrocarbon generation and migration time. According to priority of the formation time or occurrence time of geological part of reservoir, the key dating technologies to determine source rocks age, hydrocarbon generating time, charging time, reservoir adjustment and stabilization time are established. By means of dating technologies, the key time including source rocks age, hydrocarbon charging time, gas reservoir adjustment and stabilization time are