This paper presents a novel mechanism for reservoir souring which is based on the evolution of acid gas from sour aqueous phases present in the reservoir. Souring is a widespread phenomenon in seawater floods. The accepted mechanism in these cases is biogenic activity of sulfate reducing bacteria (SRB).
Field data from the Caroline reservoir indicate that it is souring. What is intriguing about this field is that it is being developed via conventional blowdown depletion, which suggests that SRB is not the cause. The mechanism presented is based on the physical principles of Henry's Law, which govern the solubility of hydrogen sulfide (H2S) in water.
Through material balance analysis and reservoir simulation, the Caroline field is presented as a case study where this mechanism is plausible. Reservoir simulation which account for this phenomenon was subsequently used to generate more realistic gas composition, thus optimizing the operations of the $1 billion Caroline facility.