Quantitative assessment of source rock maturity with multiple aromatic parameters: a case study of Mesozoic source rocks in Yingen-Ejinaqi Basin

Abstract

Aromatic parameters have been widely applied to assess the maturity of organic matters. Some parameters may not only be affected by maturation, but also more affected by organic matter source, sedimentary environment, etc. Therefore, the application effect of some parameters in some study areas were not satisfying, and the previous relational expression to calculate the vitrinite reflectance (Rc) which only based on a single parameter is also not suitable for other areas. In this study, we proposed a method to improve the accuracy of using multiple aromatic parameters to quantitatively evaluate source rock maturity. This method was based on a certain number of GC-MS analysis data of aromatic fractions of source rocks in the study area, to find out a most sensitive parameter to maturity in three categories of aromatics (alkyl naphthalene series, alkyl phenanthrene series and alkyl dibenzothiophene series) respectively. Here the most sensitive parameter meant having the largest correlation coefficient to Ro in certain category. Then a multiple linear regression equation was established among these three parameters and Ro using a numerical analysis software, and with this equation Rc can then be calculated with multiple parameters. This method is applied to the study of Mesozoic lacustrine source rocks in the Hari Sag of Yingen-Ejinaqi Basin, the organic matter types of these source rock are mainly type Ⅱ1-Ⅱ2. The results indicated that the correlation coefficient (Rc) between Ro and Rc which was calculated by established formula was as high as 0.96, and compared with the single aromatics parameter, the correlation coefficient has been considerably improved.

Keywords

• maturity parameters of polycyclic aromatic
• multiple regression method
• quantitative evaluation
• maturity of source rock
• yingen-ejinaqi basin