海相高-过成熟烃源岩成熟度判识新指标的研究

Now, the issue of deep - marine original oil and gas exploration has become the hot issue in the world. The classification scheme of thermal- evolutionary stages for the hydrocarbon source rocks is an important parameters to assess the resource in sedimentary basins, and it is also vital to guide the exploration of oil and gas. But the lack of vitrinite in marine strata, the vitrinite reflectance (Ro) has lost effectiveness to determine the maturity of marie source rocks. Furthermore, the marine strata in China is of old age and in high evolution period, and the application of maturity parameters based on biomarkers is limited. The diadamantane index is also invalid. The reason is that either biomarkers are at their equilibrium values or the compounds employed in the parameters are thermally destroyed at the high mature and overmature stage. The normal biomarkers can no longer be used to assess the maturity of those high mature and overmature samples. Thus, looking for new maturity indices is getting more desperate. In the early work, we has gotten some satisfactory results. It showed that linear relationship was fitted well between the pristane isomerization ratio (PIR) and the Ro value in those high mature and overmature coal rocks, with a high coefficient of 0.9951. As a result, our results suggest that the diastereoisomer of acyclic isoprenoids may be an appropriate indicator of maturity for the high mature and overmature source rocks. Therefore, this project will analyse comprehensively the different types of rock profiles and the thermal simulation samples. In addition, the relationship between the isomerization index and the Ro value will be created by studying the parameters of pyrolysis dynamics. Finally, optimizing a new comprehensive maturity evaluation system for highly mature and overmature marine source rocks, and use it to evaluate these marine source rocks in China. Therefore, it has broader and brighter application prospects in guiding future oil and gas exploration of marine strata in China.

深层海相油气是当前国内外勘探的热点。烃源岩热演化阶段的划分对于评价盆地资源并指导勘探至关重要。海相地层镜质体缺乏，很难获得可靠的成熟度指标-镜质体反射率（Ro值）；沥青等代用指标准确性很低；加之我国海相地层成熟度普遍偏高，其他常用成熟度指标（包括金刚烷指标）也相继失效，因此寻找新的成熟度指标迫在眉睫。我们前期工作观察到，当Ro值接近3%时，姥鲛烷非对映异构体比值与Ro值之间仍保持良好的线性关系，因此推测，无环类异戊二烯烷烃非对映异构体含量变化有可能成为较高演化阶段成熟度指标。本项目拟对不同类型剖面进行系统研究，并通过系统热模拟实验，摸清无环类异戊二烯烷烃非对映异构体异构化指数与Ro值之间的对应关系，并辅以热解动力学研究，建立非对映异构体异构化指数与Ro值之间的对应关系式，优选出一套新的高-过成熟烃源岩成熟度综合评价体系，并应用于我国海相高过成熟烃源岩评价。

在石油科学的研究中，油源对比及烃源岩演化程度的划分均是指导盆地油气勘探、进行油气资源量评价的关键因素，如能确定深层油气的油源，对于寻找新的油气田、增加石油、天然气产量、缓解我国石油进口压力具有重要的意义。而海相高-过成熟原油及烃源岩由于缺乏镜质体，国际上信誉度比较高的成熟度指标镜质体反射率已无能为力。由于成熟度过高，常规的可作为成熟度指标的生物标志化合物指数如甾烷和藿烷指标等达到平衡而失效，因此海相高-过成熟原油及烃源岩成熟度的判识也是多年来世界油气勘探领域急需解决的难题。针对海相高-过成熟原油和烃源岩常规生物标志化合物指标失效的问题，本项目采用GC-MS和分子筛络合技术，对不同干酪根类型的热模拟演化系列样品和天然样品中类异戊二烯烷烃的非对映异构体进行分析，并对其异构化指数与镜质体反射率的相关性进行精确、系统地研究。获取了异构化指数与成熟度之间的对应关系式及变化曲线，以镜质体反射率为纽带，建立了类异戊二烯烷烃异构体异构化指数与成熟度之间的对应关系，确立了新的海相高-过成熟度指标，并将这一成果应用于四川盆地东部震旦系-下古生界烃源岩成熟度的确定，为实现更精细、更准确、更科学的油气资源评价提供重要信息和科学依据。