固体沥青反射率与镜质体反射率的等效关系评价

Evaluation of equivalent relationship between vitrinite reflectance and solid bitumen reflectance

为揭示海相烃源岩固体沥青反射率与镜质体反射率之间的等效关系,以四川盆地志留系龙马溪组页岩为例,综合应用无水热模拟实验、有机质光学特征和反射率测试等分析,在对比前人自然演化和热模拟条件下固体沥青反射率与镜质体反射率关系的基础上,分析了无水热模拟实验前后,城口庙坝剖面龙马溪组页岩中固体沥青反射率与等同成熟度煤样中镜质体反射率的变化,建立了固体沥青反射率与镜质体反射率之间的等效关系,认为龙马溪组页岩均质状固体沥青反射率和镜质体反射率在高-过成熟阶段(VRo>1.5%)近似一致。研究结果表明:随着模拟温度(350,400,450,500℃)的升高,均质状固体沥青(后油沥青)与等同成熟度的镜质体反射率分别从1.21%和1.07%升高至3.21%和3.36%,二者的值始终近似相等并且具有良好的线性相关关系(VRo=1.125BRo-0.2062)。龙马溪组页岩中固体沥青的形成与赋存特征及其与镜质体的反射率等效关系对我国南方高演化龙马溪组页岩的成熟度的确定提供重要依据。

In order to reveal the equivalent relationship between the reflectance of solid bitumen and vitrinite,taking the Silurian Longmaxi shale in Sichuan Basin is taken as an example,anhydrous thermal simulation experiment,optical characterization of organic matterand reflectance measurement were conducted in this paper.On the basis of comparing the previous research results on both solid bitumen reflectance and vitrinite reflectance from thermal simulation series and natural evolution series,it is noticed that solid bitumen reflectance of Longmaxi shale collected from Chengkou miaoba outcrop in the northeast of Sichuan basin and vitrinite in coal with similar maturity before and after anhydrous thermal simulated temperature varied.The equivalent relationship between the reflectance of solid bitumen and vitrinite is thus established.It indicates that the value of homogeneous solid bitumen reflectance of Longmaxi shale is consistent with that of the vitrinite reflectance for the Longmaxi shale at the stage of high-over maturation(VRo>1.5%).The results showed that with the increase of the simulated temperatures(350℃,400℃,450℃ and 500℃),the reflectance of homogenous solid bitumen(post-oil solid bitumen)and vitrinite reflectance with equivalent maturity increased from 1.21%and 1.07%to 3.21%and 3.36%,respectively.The values of the two are always approximately equal and show a good linear correlation(VRo=1.125BRo-0.2062).The characteristics of the formation and occurrence of solid bitumen for Longmaxi shale and the equivalent relationship between solid bitumen reflectance and vitrinite reflectance provide an important basis for determining the maturity of the over-matured Longmaxi shale in southern China.