Study On The Bio-Control Technology Of Sulfate-Reducing Bacteria In Oilfield

Corrosion and sulfide pollution derived from the colonization of sulfate reducing bacteria (SRB) in the water injecting system, it can cause significant production problems and safety hazards in the oil industry.Hydrogen sulfide gas in even relatively small concentrations can be deadly when encountered unexpectedly in the field. It can also cause rapid corrosion of down hole and surface equipment. Iron sulfide scale often causes.Currently, chemical antiseptics have being widely used to control SRB. However, such actions cost much and bring serious environmental problems. The harm caused by SRB is much more serious in Daqing Oilfield. So, it is very important to study the dominant SRB population and bio-control technique for elimination of SRB.In this study, the microbial diversity, especially the SRB population dynamics in the water injecting system from Sa Nan, Daqing Oilfield, was evaluated by using classic microbial culturing methods combining with modern molecular techniques. Dominant SRB and denitrifying bacteria (DNB) were isolated and identified. Moreover, bio-control of SRB by using nitrate/nitrite and DNB were studied primarily with constructed competitive inhibition system. Main results are as follow:(1) The growth of SRB mainly occurred in the surface producing water treatment system. Bacteria community structure as well as SRB populations changed during the surface treatment processes. (2) A gram-positive, spore-forming SRB strain SRB-2 was isolated from producing water, which was dominant culturable SRB. The closest phylogenetic relative of strain SRB-2 was Garciella nitratireducens gen. nov., with 99% of 16S rDNA sequence similarity.But SRB-2 has the ablility to reduce sulfate which is physiologically different from its closest relatives.(3) A heterotrophic denitrifying bacteria DNB-1 was isolated and identified as Pseudomonas putida by 16S rRNA gene sequence analysis. Co-culture of autotrophic denitrifying bacteria was also obtained. (4) H₂S production was decreased effectively with nitrate/nitrite amendment (0.5 g/l¹.0 g/l and 0.1 g/L ¹.0 g/L), indicating that DNB-1 can competitively inhibit SRB-2 activity. The inhibition effect was retained for more than 10 days,and 85% H₂S production was decreased; DNB-1 can inhibit SRB-2 activity and H₂S production within 10 days with 0.1 g/L⁰.25 g/L nitrate amendment and 65% H₂S production was decreased. The inhibition effects of nitrite were better than that of nitrate. Molybdate concentration of 0.5 g/L can also inhibit the growth of SRB-2. (5) The addition of 0.1 g/L of nitrate or nitrite together with DNB-1 into the produced water could decrease H₂S production effectively; It can also inhibit SRB activity in shorter time without adding DNB-1 to the system.All the results showed that the supplementation of nitrate or nitrite combining with denitrifying bacteria addition could effectively inhibit the number and activity of SRB present in the injecting water system.