Geochemical characterization of natural gases in the pre-salt section of the Santos Basin (Brazil) focused on hydrocarbons and volatile organic sulfur compounds

Igor V.A.F. Souza; Geoffrey S. Ellis; Alexandre A. Ferreira; Jarbas V.P. Guzzo; Rut A. Díaz; Ana Luiza S. Albuquerque; Alon Amrani

doi:10.1016/j.marpetgeo.2022.105763

Geochemical characterization of natural gases in the pre-salt section of the Santos Basin (Brazil) focused on hydrocarbons and volatile organic sulfur compounds

Igor V.A.F. Souza^*, Geoffrey S. Ellis, Alexandre A. Ferreira, Jarbas V.P. Guzzo, Rut A. Díaz, Ana Luiza S. Albuquerque, Alon Amrani

^*Corresponding author for this work

Fredy & Nadine Herrmann Institute of Earth Sciences

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

5 Scopus citations

Abstract

The objective of this work is to characterize the geochemistry of a suite of natural gas samples from five fields in order to improve the understanding of the lacustrine petroleum system of the pre-salt section from the Santos Basin (Brazil). Additionally, the distribution of volatile organic sulfur compounds (VOSC) in petroleum reservoirs was examined to investigate possible applications to petroleum systems assessments. The hydrocarbon gases were generated by thermogenic processes associated with the oil window. The ¹³C-enriched values for C₁ (>−40‰) were interpreted as an organic source signature rather than an indication of thermal maturity, except for the oil occurrence (Field B), where a different fluid charge mainly composed of methane and CO₂ from a minor external kitchen area in the Santos Basin was identified. The molecular composition and the carbon and hydrogen isotopic data of the hydrocarbon gases, when combined with the VOSC molecular compositional data, allow the identification of four gas families associated with different kitchens and/or migrations pathways. The total VOSC concentrations range from 0.7 to 23.9 ppm by volume (ppmV). The organic sulfides are mainly composed of carbonyl sulfide (COS) and diethyl sulfide. The main thiol compound is ethanethiol. The cyclic VOSC are primarily composed of thiophene, with a negligible amount of branched thiophenes (<0.1 ppmV). H₂S showed a strong positive Pearson's correlation with COS and methanethiol (MeSH) concentrations (r = 0.943 and 0.807, respectively). This suggests that COS and MeSH formation was linked to H₂S generation and/or post-catagenetic interactions between hydrocarbons and H₂S, mainly related to thermochemical sulfate reduction (TSR). In contrast, the distribution of higher molecular weight VOSC seems to be controlled by source rock facies, rather than H₂S concentration. Principal component analysis of the VOSC compositional data identified some subgroups within the gas families mainly associated with TSR. The results presented in this work reveal that VOSC can be an important auxiliary tool in petroleum system studies.

Original language	American English
Article number	105763
Journal	Marine and Petroleum Geology
Volume	144
DOIs	https://doi.org/10.1016/j.marpetgeo.2022.105763
State	Published - Oct 2022

Bibliographical note

Funding Information:
We are thankful to Petrobras Research Center for supporting this project and for providing the infrastructure and laboratory facilities for the natural gas analyses. We thank the USGS for stimulating this type of scientific project and Petrobras for the permission to publish this paper. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001 . We thank the U.S.-Israel Energy Center ( BIRD Foundation ) for partial support of this study. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Funding Information:
We are thankful to Petrobras Research Center for supporting this project and for providing the infrastructure and laboratory facilities for the natural gas analyses. We thank the USGS for stimulating this type of scientific project and Petrobras for the permission to publish this paper. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001. We thank the U.S.-Israel Energy Center (BIRD Foundation) for partial support of this study. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Publisher Copyright:
© 2022 The Authors

Keywords

Gas geochemistry
HS
Petroleum systems
Pre-salt
Santos basin
Sulfides
Thermochemical sulfate reduction (TSR)
Thiols
Thiophenes
Volatile organic sulfur compounds (VOSC)

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10.1016/j.marpetgeo.2022.105763

Cite this

Souza, I. V. A. F., Ellis, G. S., Ferreira, A. A., Guzzo, J. V. P., Díaz, R. A., Albuquerque, A. L. S., & Amrani, A. (2022). Geochemical characterization of natural gases in the pre-salt section of the Santos Basin (Brazil) focused on hydrocarbons and volatile organic sulfur compounds. Marine and Petroleum Geology, 144, Article 105763. https://doi.org/10.1016/j.marpetgeo.2022.105763

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title = "Geochemical characterization of natural gases in the pre-salt section of the Santos Basin (Brazil) focused on hydrocarbons and volatile organic sulfur compounds",

abstract = "The objective of this work is to characterize the geochemistry of a suite of natural gas samples from five fields in order to improve the understanding of the lacustrine petroleum system of the pre-salt section from the Santos Basin (Brazil). Additionally, the distribution of volatile organic sulfur compounds (VOSC) in petroleum reservoirs was examined to investigate possible applications to petroleum systems assessments. The hydrocarbon gases were generated by thermogenic processes associated with the oil window. The 13C-enriched values for C1 (>−40‰) were interpreted as an organic source signature rather than an indication of thermal maturity, except for the oil occurrence (Field B), where a different fluid charge mainly composed of methane and CO2 from a minor external kitchen area in the Santos Basin was identified. The molecular composition and the carbon and hydrogen isotopic data of the hydrocarbon gases, when combined with the VOSC molecular compositional data, allow the identification of four gas families associated with different kitchens and/or migrations pathways. The total VOSC concentrations range from 0.7 to 23.9 ppm by volume (ppmV). The organic sulfides are mainly composed of carbonyl sulfide (COS) and diethyl sulfide. The main thiol compound is ethanethiol. The cyclic VOSC are primarily composed of thiophene, with a negligible amount of branched thiophenes (<0.1 ppmV). H2S showed a strong positive Pearson's correlation with COS and methanethiol (MeSH) concentrations (r = 0.943 and 0.807, respectively). This suggests that COS and MeSH formation was linked to H2S generation and/or post-catagenetic interactions between hydrocarbons and H2S, mainly related to thermochemical sulfate reduction (TSR). In contrast, the distribution of higher molecular weight VOSC seems to be controlled by source rock facies, rather than H2S concentration. Principal component analysis of the VOSC compositional data identified some subgroups within the gas families mainly associated with TSR. The results presented in this work reveal that VOSC can be an important auxiliary tool in petroleum system studies.",

keywords = "Gas geochemistry, HS, Petroleum systems, Pre-salt, Santos basin, Sulfides, Thermochemical sulfate reduction (TSR), Thiols, Thiophenes, Volatile organic sulfur compounds (VOSC)",

author = "Souza, {Igor V.A.F.} and Ellis, {Geoffrey S.} and Ferreira, {Alexandre A.} and Guzzo, {Jarbas V.P.} and D{\'i}az, {Rut A.} and Albuquerque, {Ana Luiza S.} and Alon Amrani",

note = "Funding Information: We are thankful to Petrobras Research Center for supporting this project and for providing the infrastructure and laboratory facilities for the natural gas analyses. We thank the USGS for stimulating this type of scientific project and Petrobras for the permission to publish this paper. This study was financed in part by the Coordena{\c c}{\~a}o de Aperfei{\c c}oamento de Pessoal de N{\'i}vel Superior – Brasil (CAPES) – Finance Code 001 . We thank the U.S.-Israel Energy Center ( BIRD Foundation ) for partial support of this study. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Funding Information: We are thankful to Petrobras Research Center for supporting this project and for providing the infrastructure and laboratory facilities for the natural gas analyses. We thank the USGS for stimulating this type of scientific project and Petrobras for the permission to publish this paper. This study was financed in part by the Coordena{\c c}{\~a}o de Aperfei{\c c}oamento de Pessoal de N{\'i}vel Superior – Brasil (CAPES) – Finance Code 001. We thank the U.S.-Israel Energy Center (BIRD Foundation) for partial support of this study. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Publisher Copyright: {\textcopyright} 2022 The Authors",

year = "2022",

month = oct,

doi = "10.1016/j.marpetgeo.2022.105763",

language = "American English",

volume = "144",

journal = "Marine and Petroleum Geology",

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T1 - Geochemical characterization of natural gases in the pre-salt section of the Santos Basin (Brazil) focused on hydrocarbons and volatile organic sulfur compounds

AU - Souza, Igor V.A.F.

AU - Ellis, Geoffrey S.

AU - Ferreira, Alexandre A.

AU - Guzzo, Jarbas V.P.

AU - Díaz, Rut A.

AU - Albuquerque, Ana Luiza S.

AU - Amrani, Alon

N1 - Funding Information: We are thankful to Petrobras Research Center for supporting this project and for providing the infrastructure and laboratory facilities for the natural gas analyses. We thank the USGS for stimulating this type of scientific project and Petrobras for the permission to publish this paper. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001 . We thank the U.S.-Israel Energy Center ( BIRD Foundation ) for partial support of this study. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Funding Information: We are thankful to Petrobras Research Center for supporting this project and for providing the infrastructure and laboratory facilities for the natural gas analyses. We thank the USGS for stimulating this type of scientific project and Petrobras for the permission to publish this paper. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001. We thank the U.S.-Israel Energy Center (BIRD Foundation) for partial support of this study. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Publisher Copyright: © 2022 The Authors

PY - 2022/10

Y1 - 2022/10

N2 - The objective of this work is to characterize the geochemistry of a suite of natural gas samples from five fields in order to improve the understanding of the lacustrine petroleum system of the pre-salt section from the Santos Basin (Brazil). Additionally, the distribution of volatile organic sulfur compounds (VOSC) in petroleum reservoirs was examined to investigate possible applications to petroleum systems assessments. The hydrocarbon gases were generated by thermogenic processes associated with the oil window. The 13C-enriched values for C1 (>−40‰) were interpreted as an organic source signature rather than an indication of thermal maturity, except for the oil occurrence (Field B), where a different fluid charge mainly composed of methane and CO2 from a minor external kitchen area in the Santos Basin was identified. The molecular composition and the carbon and hydrogen isotopic data of the hydrocarbon gases, when combined with the VOSC molecular compositional data, allow the identification of four gas families associated with different kitchens and/or migrations pathways. The total VOSC concentrations range from 0.7 to 23.9 ppm by volume (ppmV). The organic sulfides are mainly composed of carbonyl sulfide (COS) and diethyl sulfide. The main thiol compound is ethanethiol. The cyclic VOSC are primarily composed of thiophene, with a negligible amount of branched thiophenes (<0.1 ppmV). H2S showed a strong positive Pearson's correlation with COS and methanethiol (MeSH) concentrations (r = 0.943 and 0.807, respectively). This suggests that COS and MeSH formation was linked to H2S generation and/or post-catagenetic interactions between hydrocarbons and H2S, mainly related to thermochemical sulfate reduction (TSR). In contrast, the distribution of higher molecular weight VOSC seems to be controlled by source rock facies, rather than H2S concentration. Principal component analysis of the VOSC compositional data identified some subgroups within the gas families mainly associated with TSR. The results presented in this work reveal that VOSC can be an important auxiliary tool in petroleum system studies.

AB - The objective of this work is to characterize the geochemistry of a suite of natural gas samples from five fields in order to improve the understanding of the lacustrine petroleum system of the pre-salt section from the Santos Basin (Brazil). Additionally, the distribution of volatile organic sulfur compounds (VOSC) in petroleum reservoirs was examined to investigate possible applications to petroleum systems assessments. The hydrocarbon gases were generated by thermogenic processes associated with the oil window. The 13C-enriched values for C1 (>−40‰) were interpreted as an organic source signature rather than an indication of thermal maturity, except for the oil occurrence (Field B), where a different fluid charge mainly composed of methane and CO2 from a minor external kitchen area in the Santos Basin was identified. The molecular composition and the carbon and hydrogen isotopic data of the hydrocarbon gases, when combined with the VOSC molecular compositional data, allow the identification of four gas families associated with different kitchens and/or migrations pathways. The total VOSC concentrations range from 0.7 to 23.9 ppm by volume (ppmV). The organic sulfides are mainly composed of carbonyl sulfide (COS) and diethyl sulfide. The main thiol compound is ethanethiol. The cyclic VOSC are primarily composed of thiophene, with a negligible amount of branched thiophenes (<0.1 ppmV). H2S showed a strong positive Pearson's correlation with COS and methanethiol (MeSH) concentrations (r = 0.943 and 0.807, respectively). This suggests that COS and MeSH formation was linked to H2S generation and/or post-catagenetic interactions between hydrocarbons and H2S, mainly related to thermochemical sulfate reduction (TSR). In contrast, the distribution of higher molecular weight VOSC seems to be controlled by source rock facies, rather than H2S concentration. Principal component analysis of the VOSC compositional data identified some subgroups within the gas families mainly associated with TSR. The results presented in this work reveal that VOSC can be an important auxiliary tool in petroleum system studies.

KW - Gas geochemistry

KW - HS

KW - Petroleum systems

KW - Pre-salt

KW - Santos basin

KW - Sulfides

KW - Thermochemical sulfate reduction (TSR)

KW - Thiols

KW - Thiophenes

KW - Volatile organic sulfur compounds (VOSC)

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DO - 10.1016/j.marpetgeo.2022.105763

M3 - Article

AN - SCOPUS:85134308575

SN - 0264-8172

VL - 144

JO - Marine and Petroleum Geology

JF - Marine and Petroleum Geology

M1 - 105763

ER -

Geochemical characterization of natural gases in the pre-salt section of the Santos Basin (Brazil) focused on hydrocarbons and volatile organic sulfur compounds

Abstract

Bibliographical note

Keywords

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