二甲基二苯并噻吩生成实验及地球化学意义

Experiments on the generation of dimethyldibenzothiophene and its geochemical implications

二苯并噻吩类化合物(DBTs)是当前油气地球化学研究中常用的一类分子标志化合物,但因其地质成因机理尚存争论,导致与之相关的地化参数大多源自经验,缺乏理论基础。在10 MPa和200～500℃下,对3,3′-二甲基联苯和单质硫混合物进行封闭体系热模拟实验。结果表明,在无催化条件下由联苯类化合物生成DBTs具有特定的空间选择性。在地质条件下该反应所需的温度可低于200℃,因为体系压力的增加可降低反应门限温度。与实际地质样品相似,随着温度的升高,产物中不同甲基取代位的DBTs相对含量会发生变化,进而导致热成熟度参数MDR(4-/1-MDBT)先升高后降低。因此,MDR作为成熟度参数时需要结合实际地质条件,在合适的成熟度范围内使用。

Dibenzothiophene(DBT) and its homologues are important molecular markers in petroleum geochemistry. However, DBT-related geochemical indicators were derived mainly based on empirical observations due to insufficient understanding of the mechanisms through which these organosulfur compounds were generated in sedimentary environments. Thermal simulation experiments with 3,3’-dimethylbiphenyl and sulfur in closed gold tubes at 200-500 ℃ and 10 MPa afforded three main dimethyldibenzothiophene isomers(DMDBTs). Importantly, DBTs could be generated at a temperature as moderate as 200 ℃ under geological conditions, because the temperature threshold of the reaction could be reduced by increasing the system pressure. Further investigations revealed that the regioselectivity of the thiophene formation reaction was strongly influenced by temperature. This is similar to the process that occurs in natural geological systems. It should also be noted that the maturity index 4-/1-MDBT(MDR) reaches a maximum around 1.5%(Easy%R_o). It indicates that MDR index should be used in a suitable maturity regions combined with the given geological setting.