Formation of volatile organic sulfur compounds by low thermal maturation of source rocks: A geochemical proxy for natural gas

Ilya Kutuzov; Qilin Xiao; Chunfang Cai; Alon Amrani

doi:10.1016/j.marpetgeo.2023.106531

Formation of volatile organic sulfur compounds by low thermal maturation of source rocks: A geochemical proxy for natural gas

Ilya Kutuzov, Qilin Xiao, Chunfang Cai, Alon Amrani^*

^*Corresponding author for this work

Fredy & Nadine Herrmann Institute of Earth Sciences

Research output: Contribution to journal › Article › peer-review

Abstract

Volatile organic sulfur compounds (VOSC) are trace components of natural gas that can provide substantial information regarding gas origins, migration, and key processes such as H₂S generation and its occurrence in natural gas reservoirs. In the current study we demonstrate the applicability of VOSC as a proxy for gas-source rock correlations and identification of interactions between H₂S and other natural gas components. We studied the molecular and isotopic compositions of VOSC formed during low-level thermal maturation (%Ro equivalent = 0.60–0.71) of six different immature source rocks covering a variety of kerogens (types I, II, II-S and III). Anhydrous pyrolysis experiments (300 °C, 72h) were performed on all the source rocks studied, and the produced gases were analyzed for their molecular compositions and compound specific sulfur isotopes of the various VOSC formed. The formed gases were either dominated by CH₄ (32.2–49.9%) or CO₂ (31.9–46.2%) and contained a variety of alkanes in the C₂–C₅ range. H₂S formed in 6 out of 8 experiments at concentrations ranging from 0.6 to 4.3%. The results demonstrated formation of VOSC in all experiments, regardless of kerogen types or source rock lithologies. The formation of thiols (16–121.2 ppm) in the produced gas was restricted to those experiments that contained H₂S. This indicates that thiols formation is limited to gas-phase interactions between H₂S and hydrocarbons. In contrast, thiophenes formed in all experiments (14.9–1778.8 ppm) regardless of H₂S presence. Thiols preserved the δ³⁴S signal of their associated H₂S due to gas-phase interactions between the two, while thiophenes showed no interaction with the associated H₂S and instead preserved the δ³⁴S signature of the bulk kerogen (within 3.5‰ on average) of each source rock. This work demonstrates the applicability of thiophenes to act as a gas-source rock proxy for natural gas and thiols as a proxy for identification of present or paleo-interactions between natural gas and H₂S.

Original language	American English
Article number	106531
Journal	Marine and Petroleum Geology
Volume	158
DOIs	https://doi.org/10.1016/j.marpetgeo.2023.106531
State	Published - Dec 2023

Bibliographical note

Funding Information:
The authors thank Geoffrey Ellis (USGS) and Simon Emmanuel (HUJI) for providing the rock samples that were used in the present study. We thank Hadar Cohen-Sadon (HUJI) and Yoav Rosenberg (GSI) for assistance with RockEval/MC-ICPMS operation and the results interpretation. We thank Alexander Meshoulam (CALTECH) and Lubna Shawar (MIT) for useful comments and discussions that helped shaping this manuscript. A.A. is gratefully acknowledge the Israeli Science Foundation grant No. 3195/19 and the BIRD Foundation Energy Center for partial support of this study. C.C and Q.X. appreciate the grants from National Natural Science Foundation of China (grants 41961144023 and 42073066).

Funding Information:
The authors thank Geoffrey Ellis (USGS) and Simon Emmanuel (HUJI) for providing the rock samples that were used in the present study. We thank Hadar Cohen-Sadon (HUJI) and Yoav Rosenberg (GSI) for assistance with RockEval/MC-ICPMS operation and the results interpretation. We thank Alexander Meshoulam (CALTECH) and Lubna Shawar ( MIT ) for useful comments and discussions that helped shaping this manuscript. A.A. is gratefully acknowledge the Israeli Science Foundation grant No. 3195/19 and the BIRD Foundation Energy Center for partial support of this study. C.C and Q.X. appreciate the grants from National Natural Science Foundation of China (grants 41961144023 and 42073066 ).

Publisher Copyright:
© 2023 Elsevier Ltd

Keywords

Compound specific sulfur isotope analysis
Hydrogen sulfide
Natural gas
Pyrolysis
Thiols
Thiophenes
Volatile organic sulfur compounds

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10.1016/j.marpetgeo.2023.106531

Cite this

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title = "Formation of volatile organic sulfur compounds by low thermal maturation of source rocks: A geochemical proxy for natural gas",

abstract = "Volatile organic sulfur compounds (VOSC) are trace components of natural gas that can provide substantial information regarding gas origins, migration, and key processes such as H2S generation and its occurrence in natural gas reservoirs. In the current study we demonstrate the applicability of VOSC as a proxy for gas-source rock correlations and identification of interactions between H2S and other natural gas components. We studied the molecular and isotopic compositions of VOSC formed during low-level thermal maturation (%Ro equivalent = 0.60–0.71) of six different immature source rocks covering a variety of kerogens (types I, II, II-S and III). Anhydrous pyrolysis experiments (300 °C, 72h) were performed on all the source rocks studied, and the produced gases were analyzed for their molecular compositions and compound specific sulfur isotopes of the various VOSC formed. The formed gases were either dominated by CH4 (32.2–49.9%) or CO2 (31.9–46.2%) and contained a variety of alkanes in the C2–C5 range. H2S formed in 6 out of 8 experiments at concentrations ranging from 0.6 to 4.3%. The results demonstrated formation of VOSC in all experiments, regardless of kerogen types or source rock lithologies. The formation of thiols (16–121.2 ppm) in the produced gas was restricted to those experiments that contained H2S. This indicates that thiols formation is limited to gas-phase interactions between H2S and hydrocarbons. In contrast, thiophenes formed in all experiments (14.9–1778.8 ppm) regardless of H2S presence. Thiols preserved the δ34S signal of their associated H2S due to gas-phase interactions between the two, while thiophenes showed no interaction with the associated H2S and instead preserved the δ34S signature of the bulk kerogen (within 3.5‰ on average) of each source rock. This work demonstrates the applicability of thiophenes to act as a gas-source rock proxy for natural gas and thiols as a proxy for identification of present or paleo-interactions between natural gas and H2S.",

keywords = "Compound specific sulfur isotope analysis, Hydrogen sulfide, Natural gas, Pyrolysis, Thiols, Thiophenes, Volatile organic sulfur compounds",

author = "Ilya Kutuzov and Qilin Xiao and Chunfang Cai and Alon Amrani",

note = "Funding Information: The authors thank Geoffrey Ellis (USGS) and Simon Emmanuel (HUJI) for providing the rock samples that were used in the present study. We thank Hadar Cohen-Sadon (HUJI) and Yoav Rosenberg (GSI) for assistance with RockEval/MC-ICPMS operation and the results interpretation. We thank Alexander Meshoulam (CALTECH) and Lubna Shawar (MIT) for useful comments and discussions that helped shaping this manuscript. A.A. is gratefully acknowledge the Israeli Science Foundation grant No. 3195/19 and the BIRD Foundation Energy Center for partial support of this study. C.C and Q.X. appreciate the grants from National Natural Science Foundation of China (grants 41961144023 and 42073066). Funding Information: The authors thank Geoffrey Ellis (USGS) and Simon Emmanuel (HUJI) for providing the rock samples that were used in the present study. We thank Hadar Cohen-Sadon (HUJI) and Yoav Rosenberg (GSI) for assistance with RockEval/MC-ICPMS operation and the results interpretation. We thank Alexander Meshoulam (CALTECH) and Lubna Shawar ( MIT ) for useful comments and discussions that helped shaping this manuscript. A.A. is gratefully acknowledge the Israeli Science Foundation grant No. 3195/19 and the BIRD Foundation Energy Center for partial support of this study. C.C and Q.X. appreciate the grants from National Natural Science Foundation of China (grants 41961144023 and 42073066 ). Publisher Copyright: {\textcopyright} 2023 Elsevier Ltd",

year = "2023",

month = dec,

doi = "10.1016/j.marpetgeo.2023.106531",

language = "American English",

volume = "158",

journal = "Marine and Petroleum Geology",

issn = "0264-8172",

publisher = "Elsevier BV",

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TY - JOUR

T1 - Formation of volatile organic sulfur compounds by low thermal maturation of source rocks

T2 - A geochemical proxy for natural gas

AU - Kutuzov, Ilya

AU - Xiao, Qilin

AU - Cai, Chunfang

AU - Amrani, Alon

N1 - Funding Information: The authors thank Geoffrey Ellis (USGS) and Simon Emmanuel (HUJI) for providing the rock samples that were used in the present study. We thank Hadar Cohen-Sadon (HUJI) and Yoav Rosenberg (GSI) for assistance with RockEval/MC-ICPMS operation and the results interpretation. We thank Alexander Meshoulam (CALTECH) and Lubna Shawar (MIT) for useful comments and discussions that helped shaping this manuscript. A.A. is gratefully acknowledge the Israeli Science Foundation grant No. 3195/19 and the BIRD Foundation Energy Center for partial support of this study. C.C and Q.X. appreciate the grants from National Natural Science Foundation of China (grants 41961144023 and 42073066). Funding Information: The authors thank Geoffrey Ellis (USGS) and Simon Emmanuel (HUJI) for providing the rock samples that were used in the present study. We thank Hadar Cohen-Sadon (HUJI) and Yoav Rosenberg (GSI) for assistance with RockEval/MC-ICPMS operation and the results interpretation. We thank Alexander Meshoulam (CALTECH) and Lubna Shawar ( MIT ) for useful comments and discussions that helped shaping this manuscript. A.A. is gratefully acknowledge the Israeli Science Foundation grant No. 3195/19 and the BIRD Foundation Energy Center for partial support of this study. C.C and Q.X. appreciate the grants from National Natural Science Foundation of China (grants 41961144023 and 42073066 ). Publisher Copyright: © 2023 Elsevier Ltd

PY - 2023/12

Y1 - 2023/12

N2 - Volatile organic sulfur compounds (VOSC) are trace components of natural gas that can provide substantial information regarding gas origins, migration, and key processes such as H2S generation and its occurrence in natural gas reservoirs. In the current study we demonstrate the applicability of VOSC as a proxy for gas-source rock correlations and identification of interactions between H2S and other natural gas components. We studied the molecular and isotopic compositions of VOSC formed during low-level thermal maturation (%Ro equivalent = 0.60–0.71) of six different immature source rocks covering a variety of kerogens (types I, II, II-S and III). Anhydrous pyrolysis experiments (300 °C, 72h) were performed on all the source rocks studied, and the produced gases were analyzed for their molecular compositions and compound specific sulfur isotopes of the various VOSC formed. The formed gases were either dominated by CH4 (32.2–49.9%) or CO2 (31.9–46.2%) and contained a variety of alkanes in the C2–C5 range. H2S formed in 6 out of 8 experiments at concentrations ranging from 0.6 to 4.3%. The results demonstrated formation of VOSC in all experiments, regardless of kerogen types or source rock lithologies. The formation of thiols (16–121.2 ppm) in the produced gas was restricted to those experiments that contained H2S. This indicates that thiols formation is limited to gas-phase interactions between H2S and hydrocarbons. In contrast, thiophenes formed in all experiments (14.9–1778.8 ppm) regardless of H2S presence. Thiols preserved the δ34S signal of their associated H2S due to gas-phase interactions between the two, while thiophenes showed no interaction with the associated H2S and instead preserved the δ34S signature of the bulk kerogen (within 3.5‰ on average) of each source rock. This work demonstrates the applicability of thiophenes to act as a gas-source rock proxy for natural gas and thiols as a proxy for identification of present or paleo-interactions between natural gas and H2S.

AB - Volatile organic sulfur compounds (VOSC) are trace components of natural gas that can provide substantial information regarding gas origins, migration, and key processes such as H2S generation and its occurrence in natural gas reservoirs. In the current study we demonstrate the applicability of VOSC as a proxy for gas-source rock correlations and identification of interactions between H2S and other natural gas components. We studied the molecular and isotopic compositions of VOSC formed during low-level thermal maturation (%Ro equivalent = 0.60–0.71) of six different immature source rocks covering a variety of kerogens (types I, II, II-S and III). Anhydrous pyrolysis experiments (300 °C, 72h) were performed on all the source rocks studied, and the produced gases were analyzed for their molecular compositions and compound specific sulfur isotopes of the various VOSC formed. The formed gases were either dominated by CH4 (32.2–49.9%) or CO2 (31.9–46.2%) and contained a variety of alkanes in the C2–C5 range. H2S formed in 6 out of 8 experiments at concentrations ranging from 0.6 to 4.3%. The results demonstrated formation of VOSC in all experiments, regardless of kerogen types or source rock lithologies. The formation of thiols (16–121.2 ppm) in the produced gas was restricted to those experiments that contained H2S. This indicates that thiols formation is limited to gas-phase interactions between H2S and hydrocarbons. In contrast, thiophenes formed in all experiments (14.9–1778.8 ppm) regardless of H2S presence. Thiols preserved the δ34S signal of their associated H2S due to gas-phase interactions between the two, while thiophenes showed no interaction with the associated H2S and instead preserved the δ34S signature of the bulk kerogen (within 3.5‰ on average) of each source rock. This work demonstrates the applicability of thiophenes to act as a gas-source rock proxy for natural gas and thiols as a proxy for identification of present or paleo-interactions between natural gas and H2S.

KW - Compound specific sulfur isotope analysis

KW - Hydrogen sulfide

KW - Natural gas

KW - Pyrolysis

KW - Thiols

KW - Thiophenes

KW - Volatile organic sulfur compounds

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U2 - 10.1016/j.marpetgeo.2023.106531

DO - 10.1016/j.marpetgeo.2023.106531

M3 - Article

AN - SCOPUS:85173221197

SN - 0264-8172

VL - 158

JO - Marine and Petroleum Geology

JF - Marine and Petroleum Geology

M1 - 106531

ER -

Formation of volatile organic sulfur compounds by low thermal maturation of source rocks: A geochemical proxy for natural gas

Abstract

Bibliographical note

Keywords

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