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 u sually associated with deeply buried high-temperature carbonate reserv oirs 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 uncert ainties in the current understanding of TSR processes and their geolog ical significance. Reaction pathways, various reaction products, the a utocatalytic nature of TSR, and reaction kinetics are discussed. Furth ermore, various criteria for recognizing TSR effects, such as petrogra phic/diagenetic alterations and stable isotope geochemistry of the ino rganic as well as the organic reactants, are summarized and evaluated. There is overwhelming geological evidence of TSR taking place at a mi nimum temperature of 110-140 degrees C, but the temperature discrepanc y between experimental data and nature still exists. However, the exac t nature and mechanisms of catalysts which influence TSR are not known . Local H2S variations may reflect steady-state conditions dominated b y H2S buildups and flux out of the system. The latter is controlled by lithological and geological factors.