Responses of various nitrate-reducing bacteria to nitrate amendment used to control microbially-produced sulfide in oil field waters

Waterflooding, used in oil fields to enhance oil recovery, may cause "souring" because sulfate-reducing bacteria (SRB) become stimulated, reduce sulfate and produce H2S. The addition of NO3 - to produced waters can stimulate the activities of nitrate-reducing bacteria (NRB) and control sulfide production.; No study has previously described the different types of NRB in oil field waters. Three different most probable number probable number (MPN) procedures were used to enumerate planktonic NRB in oil field waters from five oil fields in western Canada. Planktonic SRB and aerobic bacteria were also enumerated. A second derivative UV absorbance method was developed and used to measure NO3- depletion in MPN media with organic compounds.; The microbial numbers in produced waters were very low in samples taken near or at wellheads and increased in aboveground facilities. Various types of NRB were detected in 16 of the 18 produced water samples. The numbers of heterotrophic NRB (HNRB) were equal to or greater than the number of nitrate-reducing, sulfide-oxidizing bacteria (NR-SOB) in 12 of 15 samples.; Nitrate-amended produced waters from three sulfide-containing western Canadian oil fields were monitored for chemical and microbiological changes. Sulfide was removed quickly from two of the oil field waters and slowly from the third. As well, NO3- addition stimulated large increases in the numbers of the HNRB and NR-SOB in two waters but only the NR-SOB were stimulated in the third water.; A MPN procedure to enumerate dissimilatory ammonium-producing, nitrate-reducing bacteria (DAP-NRB) in oil field waters was evaluated. Twelve of 18 oil field water samples contained DAP-NRB, but they were seldom detected in wellhead samples. For the nitrate-amended waters, the numbers of DAP-NRB remained a minor portion of the community.; Overall, the results from this work showed that moderate-temperature oil fields contain different types of NRB that can be cultured. Each souring oil field contained nitrate-reducing bacteria that oxidize sulfide and produce NO2- and N2O, so that nitrate amendment could be used to control H2S production by SRB.