Constraining the fluid history of a CO2-H2S reservoir: Insights from stable isotopes, REE and fluid inclusion microthermometry

Carmen Zwahlen, Cathy Hollis, Michael Lawson, Stephen P Becker, Adrian Boyce, Zheng Zhou, Greg Holland

    Research output: Contribution to journalArticlepeer-review

    53 Downloads (Pure)


    Reservoirs that host CO2-H2S bearing gases provide a key insight into crustal redox reactions such as thermochemical sulphate reduction (TSR). Despite this, there remains a poor understanding of the extent, duration and the factors limiting this process on a reservoir scale. Here we show how a combination of petrography, fluid inclusion, rare earth element (REE) and carbon (δ13C), oxygen (δ18O) and sulphur (δ3424 S) stable isotope data can disentangle the fluid history of the world's largest CO2 accumulation, the LaBarge Field in Wyoming, USA. The carbonate hosted LaBarge Field was charged with oil around 80 Ma ago, which together with nodular anhydrite, represent the reactants for TSR. The nodules exhibit two distinct trends of evolution in δ13C with both δ34S and δ1827 O that may be coupled to two different processes. The first trend, was interpreted to reflect the coupled dissolution of anhydrite and reduction to elemental sulphur and the oxidation of organic compounds and associated precipitation of calcite during TSR. In contrast, the second trend was interpreted to be the result of the hydrothermal CO2 influx after the cessation of TSR. In addition, mass balance calculations were performed to estimate an approximate TSR reaction duration of 80 ka and to identify the availability of organic compounds as the limiting factor of the TSR process. Such an approach provides a tool for the prediction of TSR occurrence elsewhere and advancing our understanding of crustal fluid interactions.
    Original languageEnglish
    JournalGeochemistry, Geophysics, Geosystems
    Early online date19 Dec 2018
    Publication statusPublished - 16 Jan 2019


    Dive into the research topics of 'Constraining the fluid history of a CO2-H2S reservoir: Insights from stable isotopes, REE and fluid inclusion microthermometry'. Together they form a unique fingerprint.

    Cite this