Abstract
Microbial activities in oil and gas operations cause souring, the production of sulfide by sulfate-reducing bacteria (SRB), and microbiologically-influenced corrosion (MIC). MIC may be especially severe in systems were several different types of fluids are mixed together, as this may provide a variety of nutrients for microbial growth. We have studied samples from an offshore production site and an onshore terminal for separation, crude oil storage, effluent treatment and disposal. We have investigated the samples using chemical analyses, culture-based microbial counts and molecular DNA-based techniques (pyrosequencing) to obtain whole microbial community composition. We found that (i) sulfate reduction by SRB (Desulfovibrio, Desulfobacterium, Desulfobacter) leads to the formation of sulfide, that (ii) sulfide is reoxidized to form elemental sulfur both abiotically and through the metabolism of sulfide-oxidizing bacteria (Sulfurimonas, Arcobacter) and that (iii) sulfur is converted back to sulfide by sulfur-reducing bacteria (S0RB, Desulfuromonas, Desulfuromusa), completing the sulfur cycle. Samples from these systems have significant sulfate, sulfide and sulfur (S8) concentrations and reactions (i) to (iii) can be demonstrated to occur. We find that the presence of elemental sulfur, which is increased by reactions (i) and (ii) and decreased by reaction (iii) gives rise to considerably increased corrosion risk towards steel infrastructure.
