Inhibiting The Activity Of Sulfate-reducing Bacteria Present In Produced Water By NO₃^-or NO₂^-

Sulfate-reducing bacteria (SRB) are varieties of prokaryotes that use sulfate asthe sole electron acceptor for growth and energy metabolism. SRB could utilizevarious organics as carbon sources, and are distributed widely in anoxic or anaerobicenvironments including oil reservoirs and produced waters. As water-floodingpractices for oil recovery go on, the sulfate present in the injection water stimulatesthe growth and activity of SRB, producing H2S, thereby leading to souring, microbialcorrosion, and eventually induces various environmental problems and productionconcerns. Effectively and efficiently controlling the activity of SRB remains one ofthe greatest challenges for oil industry.In recent years, a biological-inhibition-method based on stimulating the activitiesof nitrate-reducing bacteria (NRB) to inhibit SRB has attracted much attention.Addition of nitrate or nitrite could stimulate the heterotrophic NRB (hNRB) whichcompetitively inhibit the SRB for organic carbons. Additionally, the presence ofnitrate also triggers the growth of the nitrate-reducing, sulfide-oxidizing bacteria(NR-SOB) which will further eliminate the produced H2S. Nevertheless, theheterogeneities of oil reservoirs together with the diverisities of SRB determine thecomplexity and uncertainty of nitrate for the control of SRB. Hence, it is better to finetune the control strategy according to the real conditions of the specific oil reservoir.Considering the properties of the produced water in Daqing Oilfield, this studyfocused on the metabolic characteristics of SRB, and investigated the efficiency andmechanisms of inhibition of SRB based on nitrate or nitrite that stimulated the activityof NRB. The results showed that the SRB in the produced water from Daqing Oilfieldexihibited high activity of sulfate reduction. The SRB could also reduce nitrate toammonium; under abundant organic carbon conditions, the dominat NRB strainNRB-8could hardly inhibit the strain SRB-6. Addition of low concentration of nitratedid. By contrast, under organic carbon-limit conditions, the competitively inhibitionof NRB for organics over SRB was responsible for the control of SRB. In this case, the presence of nitrate, even in low concentration, could reduce the production of H2S;the introduction of NRB-8would further decrease the content of H2S.