Transformation of iron sulfide by oil field microorganisms and their inhibition by sulfur/polysulfide

Abstract

Iron sulfide (FeS) causes problems in oil reservoirs. Nitrate reducing-sulfide oxidizing bacteria (NR-SOB) cannot remove precipitated FeS, though they are able to utilize dissolved sulfide. However, nitrite, the product of NR-SOB can promote the transformation of FeS to greigite (Fe3S4) with the help of sulfate-reducing bacteria (SRB). The role of SRB in this transformation is to convert amorphous FeS to tetragonal FeS, mackinawite. Nitrite chemically reacts with sulfide, the product of SRB to form sulfur/polysulfide, which then works as a weak oxidant to transform mackinawite to greigite. In addition, sulfur/polysulfide, the reaction product of nitrite with sulfide is an inhibitor of SRB growth, but not all SRB are inhibited by sulfur/polysulfide. The hep] and hcp2 genes, which encode hybrid cluster proteins, are involved in the metabolism of sulfur/polysulfide. SRB with these genes are able to overcome the inhibition from sulfur/polysulfide, whereas mutant strains lacking these genes are more severely inhibited.