Composition Characteristics and Geochemical Significance of Thiophene-type Compounds for Crude Oils in Tarim Basin

Key words: 
• dibenzothiophene /
• marine oil /
• lacustrine oil /
• coal-forming oil /
• Tarim Basin

Abstract: The relative abundance and composition characteristics of thiophene-type compounds for typical crude oils in Tarin Basin were analysed and studied systematically using GC-MS-MS technique. The results suggest the relative abundance between benzonaphiothiophene and dibenzothiophene series of % toatal polycyclic aromatic hydrocarbons for different types of crude oils are obvious differences,the contents of marine oils are the higest,contents of lacustrine oils are lower and that of coal-forming oils are the lowest.In this paper,we propose some new organic geochemical parameters for distinguishing marine oil and lacustrine oil using the ratio values of 4-dimethyldibenzothiophene(MDBT)/dibenzothiophene(DBT) as well as (2+3)-MDBT/DBT,for distinguishing marine marl-sourced oil and marine carbonate-sourced oil using the ratio value of 1-MDBT/DBT.Marine oils and coal-forming oils show a predominance of alkylated DBT homologues over the unsubstituted parent,but laustrine oils differ from marine oils and coal-forming oils.However,the maximum degree of alkylation(the most abundance alkylation homologues within any given DBT series) varies,marine oils show a high degree of alkylation,which non-marine oils generally exhibit a lower degree of alkylation.So there is increasing decrease trends from marine marl-sourced oils and marine carbonat-sourced oils to laustrine oils and coal-forming oils.We propose that alkylation trends reflect differences of crosslinking or branching on aliphatic and cyclic moieties in sulfur-rich vs.sulfur-poor kcrogens.