Oil maturity assessment using maturity indicators based on methylated dibenzothiophenes

摘要: Aromatic fractions of 140 oils and condensates that originated from different types source rocks (marine shale, terrestrial shale marine carbonate) were analyzed using gas chromatographymass spectrometry (GC-MS) to investigate the relative distributions methylated dibenzothiophenes with respect thermal maturity. The positions methyl groups trimethyldibenzothiophene isomers (TMDBTs) including those used in definition maturity indicator TMDBT index previous studies firmly identified by co-elution internal standards GC-MS analysis comparing reported retention indices. A new ratio related dimethyldibenzothiophenes (DMDBTs) is proposed on basis differences thermodynamic stability among DMDBT isomers. Another (TMDBT-I2) based TMDBTs also suggested our empirical observations presumed These two newly (2,6 + 3,6)-/l,4-DMDBT TMDBT-I2 correlate well MDR (4-/l-methyldibenzothiophene) 2,4-/1,4-DMDBT ratios, suggesting their common chemical reaction mechanisms similar behavior increasing Therefore, they can be effectively applied for assessments. Furthermore, parameters are more reliable over-mature due relatively higher concentrations thermodynamically unstable isomers, i.e. 1,4,6-, 1,4,8- 3,4,6-TMDBT this study than 1-methyldibenzothiophene (1-MDBT) or 1,4-DMDBT. In contrast 4,6-/1,4-DMDBT, 3,6)-/1,4-DMDBT ratios have approximately same relationship oil (Rc %). This suggests lithology organic facies may less influence compared 4,6-/1,4-DMDBT. particularly useful assessments post- complement indicators steranes terpanes.