Abstract
Seawater injection into oil reservoirs for secondary oil recovery is frequently accompanied by souring (increased sulfide concentrations). Production of hydrogen sulfide causes various problems, such as microbiologically influenced corrosion (MIC), deterioration of crude oil. Sulfate-reducing bacteria (SRB) are considered to be major players in souring. Volatile fatty acids (VFAs) in oil field water are assumed to be produced by microbial degradation of crude oil. The objective of this research is to investigate mechanisms of souring from the view of VFA production by the crude oil biodegradation. A microbial consortium collected from oil-water separator was suspended to seawater. Crude oil or liquid n-alkane mixture was added to the culture medium as sole carbon source. Anaerobic incubation was conducted for 190 days. Physicochemical analysis showed that preferable toluene degradation and sulfate reduction occurred concomitantly in crude oil amended condition. Sulfide concentration was much lower in alkane mixture amended condition than that of crude oil amended condition. These observations suggest that SRB are related to toluene activation and VFA consumption steps in crude oil degradation. Therefore, the electron donors for SRB were not only VFA, but a lot of crude oil components, especially toluene. Alkanes were also degraded by microorganisms, but did not so contribute to reservoir souring.
