Oilfield Glossary
Oilfield Glossary
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sulfate-reducing bacteria

1. n. [Drilling Fluids]
A common anaerobic bacterium, commonly abbreviated SRB, that can convert sulfate ions, SO4-2, into S-2 and HS-, with the concomitant oxidation of a carbon source. The lignite, lignin, tannins, cellulose, starches and fatty acids found in many mud systems are carbon food sources for SRB. Where mud is stored, precautions should always be taken when handling or reconditioning water muds containing lignosulfonates, gypsum (sulfate sources) and starches, cellulose, xanthan gum and lignite (food sources). These muds can harbor SRB and can have high sulfide accumulations. Mud filtrate should be tested with the Garrett Gas Train to determine sulfide concentration in a stored mud, followed by treatments with caustic soda to raise pH and zinc-based scavengers to remove sulfides as ZnS. Before storage of mud, treatment with a bactericide can inhibit SRB growth. Also, circulating mud from time to time, with air entrainment, can retard development of anaerobic conditions. Anaerobic bacteria can convert the sulfate or sulfite present in water handling facilities to hydrogen sulfide [H2S]. This by-product, combined with iron, can form iron sulfide, a scale that is very difficult to remove. SRB occur naturally in surface waters, including seawater. Bacteria accumulation can lead to pitting of steel, and the buildup of H2S increases the corrosiveness of the water, thus increasing the possibility of hydrogen blistering or sulfide stress cracking.
Alternate Form: SRB