Influence of thermal maturity on carbazole distributions in coal source rocks during compaction pyrolysis experiments

Jian Bao; Yan Liu; Yunpeng Fan; Yaohui Xu; Kangle Ding; Zhigang Wen; Yang Li; Ye Gao; Cunyang Zhang; Lu Li

doi:10.1038/s41598-024-57520-1

Influence of thermal maturity on carbazole distributions in coal source rocks during compaction pyrolysis experiments

Sci Rep. 2024 Mar 21;14(1):6848. doi: 10.1038/s41598-024-57520-1.

Authors

Jian Bao^{1

2}, Yan Liu^{3

4}, Yunpeng Fan^{1

2}, Yaohui Xu^{1

2}, Kangle Ding⁵, Zhigang Wen^{1

2}, Yang Li^{1

2}, Ye Gao^{1

2}, Cunyang Zhang^{1

2}, Lu Li^{1

2}

Affiliations

¹ Hubei Key Laboratory of Petroleum Geochemistry and Environment (Yangtze University), Wuhan, 430100, Hubei, People's Republic of China.
² College of Resources and Environment, Yangtze University, Wuhan, 430100, Hubei, People's Republic of China.
³ Hubei Key Laboratory of Petroleum Geochemistry and Environment (Yangtze University), Wuhan, 430100, Hubei, People's Republic of China. liuyan@yangtzeu.edu.cn.
⁴ College of Resources and Environment, Yangtze University, Wuhan, 430100, Hubei, People's Republic of China. liuyan@yangtzeu.edu.cn.
⁵ College of Chemistry and Environmental Engineering, Yangtze University, Jingzhou, 434022, Hubei, People's Republic of China.

Abstract

Carbazole compounds are widely used in determining the direction of petroleum migration, but the effect of thermal maturity on carbazoles is still ambiguity. In this paper, using compaction pyrolysis simulation experiments, artificial mature samples with vitrinite reflectance (R_o) range from 0.38 to 3.0% were acquired. And the content and composition change characteristics of carbazole compounds were analyzed in coal source rocks. The experimental results showed that thermal maturity controls the generation of a large amount of carbazole compounds in coal rocks. Compared with the low mature stage, the content of carbazole compounds was about 10-100 times higher in the mature stage. With the increasing maturity, in the coal sample, the content of carbazole compounds showed a trend of first increasing and then decreasing. In derivatives of carbazole, the corresponding maturity for the maximum generation of ethylcarbazole (EC), dimethylcarbazole (DMCA), methylcarbazole (MCA), carbazole (CA) and benzocarbazole (BCA) performed the increasing sequence. With the increasing maturity, the relative abundance of 2-MCA, 1,7-DMCA and benzo[a]carbazole increased with the increasing maturity, while 4-MCA, 1,4-DMCA and benzo[c]carbazole gradually decreased. Benzocarbazole ratio [a]/[a] +[ c] varies only in a narrow range 0.36-0.61 in the entire maturity range, suggesting limited maturity dependence. The experimental conclusion provides more theoretical basis for future geochemical analysis using carbazole compounds.

Keywords: Carbazole compounds; Coal; Compaction pyrolysis experiment; Hydrocarbon migration; Thermal maturity.

Abstract

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