High H2S contents and other effects of thermochemical sulfate reduction in deeply buried carbonate reservoirs: a review

The accumulation of high H₂S concentrations in oil and gas fields is usually associated with deeply buried high-temperature carbonate reservoirs and is attributed to the abiological oxidation of hydrocarbons by sulfate – thermochemical sulfate reduction (TSR). This review aims at providing an overview of the literature and assessing existing uncertainties in the current understanding of TSR processes and their geological significance. Reaction pathways, various reaction products, the autocatalytic nature of TSR, and reaction kinetics are discussed. Furthermore, various criteria for recognizing TSR effects, such as petrographic/diagenetic alterations and stable isotope geochemistry of the inorganic as well as the organic reactants, are summarized and evaluated. There is overwhelming geological evidence of TSR taking place at a minimum temperature of 110–140?°C, but the temperature discrepancy between experimental data and nature still exists. However, the exact nature and mechanisms of catalysts which influence TSR are not known. Local H₂S variations may reflect steady-state conditions dominated by H₂S buildups and flux out of the system. The latter is controlled by lithological and geological factors.