甲基二苯并噻吩分布指数（MDBI）作为烃源岩成熟度标尺的探讨

选择库车坳陷和雅布赖盆地两个烃源岩热演化系列,在GC/MS分析的基础上探讨了二苯并噻吩类成熟度参数,如MDR4、MDR23、MDR、MDR’等的热演化特征,首次提出利用甲基二苯并噻吩分布指数(MDBI)作为研究区有效的新型成熟度标尺。结果表明,在成熟至高成熟阶段MDR4和MDR23主要受热力作用控制,在研究区应用效果良好;MDR在较高热演化阶段变化速率显著增加,而且适合于Ⅱ2和Ⅲ型有机质。甲基二苯并噻吩分布指数与其他有效参数,如Ro、tmax和MPI等之间的相关系数矩阵进一步证实,在Ro=0.67%～1.22%范围内,MDBI能够准确提供烃源岩热演化历史方面的信息。该指数的提出还有望为原油热成熟度的判识提供一个新的途径。

Methyldibenzothiophenes distribution index as a tool for maturity assessments of source rocks

The characteristics for the thermal evolution of dibenzothiophenes maturity parameters, such as 4 MDBT/DBT, 2,3 MDBT/DBT, 4 MDBT/1 MDBT and 4 MDBT/(4 MDBT＋ 1 MDBT), have been discussed on the basis of GC/MS analysis for the two selected suites of source rocks in Kuqa depression, Tarim basin and Yabrai basin, Hexi Zoulang area. It is the first report that methyldibenzothiophene distribution index (MDBI), namely, 4 MDBT/(DBT＋ 4 MDBT＋ 2,3 MDBT＋ 1 MDBT) increasing with the maturation, which primarily follows the principle of chemical thermodynamics, has been proposed as a new effective parameter of maturity in the investigated basin or depression. The results indicate that MDR 4 and MDR 2,3, which are thermodynamically controlled, are better maturity parameters to evaluate the thermal maturation of source rocks in the areas. It is found that the rate of MDR ratio appears a remarkable increase in a little high maturation, and MDR is very reliable for maturity determination of type Ⅱ 2 and Ⅲ of organic matters. The correlation matrix for MDBI and other effective maturity indicators, such as Ro, tmax and MPI, further demonstrates that MDBI may accurately provide the information about the history of thermal evolution for source rocks within the vitrinite reflectance (Ro) values varying from 0.67％ to 1.22％ . Moreover, the new index presented in this paper implies a new access to identify the thermal maturation of oils.