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。

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.