The influence of nitrate on microbial processes in oil industry productionwaters

Sulfide accumulation due to bacterial sulfate reduction is responsible for a number of serious problems in the oil industry. Among the strategies to c ontrol the activity of sulfate-reducing bacteria (SRB) is the use of nitrat e, which can exhibit a variety of effects. We investigated the relevance of this approach to souring oil fields in Oklahoma and Alberta in which water flooding is used to enhance oil recovery. SRB and nitrate-reducing bacteri a (NRB) were enumerated in produced waters from both oil fields. In the Okl ahoma field, the rates of sulfate reduction ranged from 0.05 to 0.16 muM S day(-1) at the wellheads, and an order of magnitude higher at the oil-water separator. Sulfide production was greatest in the water storage tanks in t he Alberta field. Microbial counts alone did not accurately reflect the pot ential for microbial activities. The majority of the sulfide production app eared to occur after the oil was pumped aboveground, rather than in the res ervoir. Laboratory experiments showed that adding 5 and 10 mM nitrate to pr oduced waters from the Oklahoma and Alberta oil fields, respectively, decre ased the sulfide content to negligible levels and increased the numbers of NRB. This work suggests that sulfate reduction control measures can be conc entrated on aboveground facilities, which will decrease the amount of sulfi de reinjected into reservoirs during the disposal of oil field production w aters.