Isotopomer approaches to the detection of anaerobic oxidation of natural gas hydrocarbons
- 1Tokyo Institute of Technology, Department of Earth and Planetary Sciences, Japan (gilbert.a.aa@m.titech.ac.jp)
- 2Tokyo Institute of Technology, Earth-Life Science Institute, Japan
- 3Tokyo Institute of Technology, Department of Environmental Chemistry and Engineering, Japan
Hydrocarbons are the main constituents of natural gas. Their chemical and isotope abundance is a window to biogeochemical processes occurring in the subsurface. Stable isotopes of natural gas hydrocarbons are traditionally measured through compound-specific isotope analysis (CSIA) where each hydrocarbon is separated before its isotope ratio is determined.
Recently a variety of methods have been developed to determine position-specific isotope composition of propane, the first hydrocarbon with two distinct isotopomers: central and terminal [1][2][3][4]. The relative abundance of propane isotopomers (e.g. Δ13Ccentral = δ13Ccentral - δ13Cterminal) is a promising tool for tracing sources and sinks of hydrocarbons in natural gas reservoirs. In particular, anaerobic oxidation of propane starts with a fumarate addition at the central position, which is expected to lead to a specific enrichment of the central 13C-isotopomer of the remaining propane.
We measured Δ13Ccentral values of propane throughout the course of its oxidation by bacteria BuS5 [5] and showed that the isotope fractionation is located mainly on the central position, which differs from the signature expected for thermogenic evolution [6]. The approach has been used to detect anaerobic oxidation of propane in several natural gas reservoirs: Southwest Ontario (Canada), Carnarvon Basin (Australia), Michigan (USA) [6], and more recently Tokamachi mud volcano in Japan [7]. In addition, isotopomers of n-butane and i-butane analysed using the same technique allows gaining insights into the mechanism of their microbial oxidation.
The isotopomer approach presented here can thus shed light on the fate of natural gas hydrocarbons. In combination with clumped isotope measurements of methane and ethane, the approach can provide unprecedented information regarding carbon cycling in the subsurface.
[1] Gilbert et al., 2016 GCA v177, p205
[2] Piasecki et al., 2016 GCA v188 p58
[3] Gao et al., 2016 Chem Geol. v435, p1
[4] Liu et al., 2018 Chem Geol. v491, p14
[5] Kniemeyer et al., 2007 Nature v449, p898
[6] Gilbert et al., 2019 PNAS v116, p6653
[7] Etiope et al., 2011 Appl. Geochem. v26, p348
How to cite: Gilbert, A., Julien, M., Yoshida, N., and Ueno, Y.: Isotopomer approaches to the detection of anaerobic oxidation of natural gas hydrocarbons, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13618, https://doi.org/10.5194/egusphere-egu2020-13618, 2020
