SULFUR-REDUCING BACTERIA MAY LOWER CORROSION RISK IN OIL FIELDS BY COUPLING OXIDATION OF OIL ORGANICS TO REDUCTION OF SULFUR-POLYSULFIDE TO SULFIDE

摘要

Sulfate-reducing bacteria are generally considered to have a profound impact on the petroleum industry as their sulfide production activity contributes to reservoir souring and pipeline corrosion. SRB can be controlled by injecting biocides into pipelines and above-ground facilities. A recent "green" alternative for controlling reservoir souring is to inject nitrate, as nitrate is relatively harmless and is ultimately reduced to nitrogen gas. Resident nitrate-reducing bacteria (NRB) reduce nitrate to nitrite, which is a strong inhibitor of SRB, thereby inhibiting sulfide production. However, NRB-mediated oxidation of sulfide with nitrate and/or chemical reaction between nitrite and sulfide can generate sulfur-polysulfide (S-PS), which can expedite corrosion. S-PS is also rapidly formed by chemical reactions, when sour produced waters, containing substantial sulfide concentrations, are exposed to air. Once formed, S-PS can be removed by either of two alternative routes, which may thus reduce corrosion risk. In the presence of (ⅰ) excess electron acceptor (e.g. nitrate), NRB may further oxidize the S-PS to sulfate, whereas in the presence of (ⅱ) excess electron donor (oil organics, e.g. acetate) the S-PS may be reduced back to sulfide. A specialized group of sulfur-reducing bacteria catalyzes this reaction. A representative of this group, Desulfuromonas acetoxidans, derives energy for growth from the reaction: 4 sulfur + acetate = 4 sulfide + 2 CO_2. Because oil field waters tend to be electron donor rich and electron acceptor poor, one would expect S-PS to be removed by the second route. A survey of the microbial community in produced waters from an oil field with low bottomhole temperatures indicated Desulfuromonas species to be common. Hence, once S-PS is formed by reaction of excess sulfide with a limiting concentration of nitrate or oxygen, it may subsequently be effectively removed through the activity of sulfur-reducing bacteria such as Desulfuromonas.