Assessment of H2S Generated by TSR Reaction in the Devonian Petroleum System of Alberta (Canada) Using Basin Modeling

Improved exploration strategies for the oil and gas fields involve high temperatures and pressures. This may induce Thermochemical Sulfate Reduction (TSR) risks. TSR is a complex succession of redox reactions that occur in deeply buried anhydrite-rich carbonate reservoirs under high temperatures. Such reactions lead to the formation of a high amount of H2S (toxic and corrosive gas) and a decrease in the quality of the hydrocarbons due to their oxidation. A new basin-scale approach was developed to compute a TSR risk index and, to assess the spatial distribution of H2S. The produced H2S can then be either dissolved in the formation water or released as a free gas phase. These two possibilities have been integrated into the TemisFlow™ software and were successfully applied to the Western Canadian Sedimentary Basin (WCSB). The Devonian carbonate reservoirs of WSCB are known to have experienced TSR reactions, some of them containing up to 30% of H2S. The obtained numerical results show high TSRI values for the Devonian petroleum system. These values increase with the burial associated to the Laramide orogeny. Our results are in agreement with the petrography analyses. Given our simulation criteria, the order of magnitude of average simulated H2S masses is the same as the one reported by Machel (2005).