EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

The origins of volatile organic sulfur compounds in natural gas reservoirs

Ilya Kutuzov1, Chunfang Cai2, and Alon Amrani1
Ilya Kutuzov et al.
  • 1Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
  • 2Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China

Volatile organic sulfur compounds (VOSC) are known to occur in natural gas and petroleum reservoirs. These compounds are typically accompanied by H2S which together, degrade the quality of the petroleum, complicate production due to corrosion of piping, and pose a health risk to workers and local communities. The origins of both H2S and VOSC in natural gas are only partially understood with the latter being analyzed in only a few cases and its formation processes virtually unknown. Nevertheless, several studies have linked VOSC to H2S in processes such as thermochemical sulfate reduction (TSR) and kerogen cracking. Hence, VOSC have the potential to act as a proxy for the natural gas and H2S origins, in-situ TSR and fluid migration pathways.

To better understand the pathways of VOSC formation in natural gas reservoirs, we analyzed natural gas samples (Permian reservoirs, Sichuan Basin, China) and performed a series of pyrolysis experiments. The results of the experiments between methane (CH4) and H2S at 360°C for 4-96 hours revealed the only VOSC formed is methanethiol (MeSH) which was identified at ppm concentrations in all experiments. The δ34S values of the MeSH were 2 to 3‰ heavier than the initial H2S. For comparison, Meshoulam et al., (2021) reported that the reaction between H2S and pentane (i.e. “wet gas”) that yielded a variety of VOSCs from thiols to methyl-thiophenes in the gas phase and up to methyl-benzothiophenes in the liquid phase. The analysis of natural gases showed that the samples contain a large variety of thiols and sulfides. The diversity of VOSC identified carries some resemblance to that observed by Meshoulam et al., (2021) and may suggest these VOSC are the result of in-reservoir reaction of C2+ hydrocarbons with H2S. The analysis of δ34S values of the VOSCs showed they cover a range between +10 to +30‰ while most samples had their VOSC in a narrower range of approximately 8‰. Generally, samples show a positive correlation between H2S content and VOSCs concentration- thereby implying VOSCs formation in the gas-phase. The δ34S of thiols in five of the samples covered a narrower isotopic range of about 2‰ while the sulfides in the samples spread over a large isotopic range of up to 10‰. This observation suggests the thiols are in isotopic equilibrium with their associated H2S while the sulfides are not. The reason for this difference is unclear. Further analysis will shed more light on isotopic fractionations between VOSC and H2S and will thus allow identification of H2S origins in the studied area.

[1] Meshoulam, A., Said-Ahmad, W., Turich, C., Luu, N., Jacksier, T., Shurki, A., Amrani, A., 2021. Experimental and theoretical study on the formation of volatile sulfur compounds under gas reservoir conditions. Organic Geochemistry, 152, 104175

How to cite: Kutuzov, I., Cai, C., and Amrani, A.: The origins of volatile organic sulfur compounds in natural gas reservoirs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9146,, 2022.