Constraining the fluid history of a CO2 -H2 S reservoir: insights from stable isotopes, REE and fluid inclusion microthermometry

Zwahlen, C., Hollis, C., Lawson, M., Becker, S. P., Boyce, A. , Zhou, Z. and Holland, G. (2019) Constraining the fluid history of a CO2 -H2 S reservoir: insights from stable isotopes, REE and fluid inclusion microthermometry. Geochemistry, Geophysics, Geosystems, 20(1), pp. 359-382. (doi: 10.1029/2018GC007900)

Abstract

Reservoirs that host CO2‐H2S‐bearing gases provide a key insight into crustal redox reactions such as thermochemical sulfate 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 sulfur (δ34S) 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 δ18O that may be coupled to two different processes. The first trend was interpreted to reflect the coupled dissolution of anhydrite and reduction to elemental sulfur 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.

• Item Type: Articles
• Keywords: Geochemistry and petrology, geophysics.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Boyce, Professor Adrian
• Authors: Zwahlen, C., Hollis, C., Lawson, M., Becker, S. P., Boyce, A., Zhou, Z., and Holland, G.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Geochemistry, Geophysics, Geosystems
• Publisher: American Geophysical Union
• ISSN: 1525-2027
• ISSN (Online): 1525-2027
• Published Online: 19 December 2018
• Copyright Holders: Copyright © 2018 American Geophysical Union
• First Published: First published in Geochemistry, Geophysics, Geosystems 20(1):359-382
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher