Impact of rock mineralogy on reservoir souring: A geochemical modeling study

The petroleum industry suffers from reservoir souring phenomena, which has negative impacts on production facilities, health, and environment. Injection of incompatible water into the reservoir (waterflooding), which is considered as an enhanced oil recovery (EOR) method, is one of the most common causes of reservoir souring. In general, injected brine, especially seawater, contains high amounts of sulfate ion (SO42-). A high concentration of sulfate in the presence of sulfate-reducing bacteria (SRB) leads to the microbial reservoir souring. During this phenomenon, sulfide, specifically hydrogen sulfide gas (H2S) appears in the producing fluid of the reservoir. In this paper, a coupled reactive transport approach is developed that contributes to studying the impact of the mineralogical composition of the rock on the souring process. The proposed model uses the geochemical software (PHREEQC) to model the interactions between the souring process and inorganic minerals including calcite, dolomite, anhydrite, pyrite, and goethite. The results of the modeling show that chalk containing anhydrite mineral produces more sulfide in comparison to limestone. The modeling also demonstrates that rock containing iron minerals (like goethite) can inhibit the sulfide generation in porous media.