Isolation Of Pseudomonas Stutzeri And Its Corrosion Behavior And Pattern On 20~# Carbon Steel In Simulated Oil Field Water

Waterflooding oil-recovery technique is the preferred recovery technique for recovering oil from reservoirs,which can maintain pressure and to push oil towards producing wells.Reinjection of production water is generally a necessity,either ecologically or economically.However,the composition of produced water is complex,which contains a small amount of crude oil,inorganic ions,metal,and microorganisms,causing potential corrosion to the pipeline and facility.Oil reservoir breed abundant microorganisms and microbiologically influenced corrosion（MIC）has been a significant part of corrosion that cannot be neglected.Sulfate-reducing bacteria（SRB）,iron bacteria（IB）,nitrate reducing bacteria（NRB）,and acid producing bacteria（APC）are the main microorganisms causing corrosion.The current knowledge focus on studies of the corrosion behavior and mechanism of SRB and static corrosion,but limited studies have been reported on corrosive iron bacteria.It is difficult to verify the dominant types of ion corrosion,biofilm corrosion and acidogenic corrosion in the corrosion process due to the complex corrosion mechanism.The produced water was collected from Changqing oilfield in this study,and incubated into Winogradsky culture medium for enrichment.Nine different strains were isolated from produced water in Changqing,including Pseudomonas,Aeromonas,Shewanella,Ochrobactrum,Sphingomonas,Bacillus,Enterobacter,Dietzia and Agrobacterium,distributed in Proteobacteria,Firmicutes and Actinobacteria,in which Pseudomonas,Aeromonas,Shewanella and Bacillus were IB.Facultative anaerobic bacteria Pseudomonas stutzeri（P.stutzeri）was selected,which has both Fe（Ⅱ）oxidation and Fe（Ⅲ）reduction functions.The effects of temperature,pH,salinity,inoculation volume and rotate speed on its growth characteristics were depicted.The results showed that the optimum growth temperature was 30 ^oC and adaptation to the high alkaline environment pH 10.0 was observed.P.stutzeri CQ-Z5 had the ability to resist the harsh environment with high salinity and alkaline environment.The ability of Fe（Ⅱ）oxidation and Fe（Ⅲ）reduction were determined.The results showed that 96.2%Fe（Ⅱ）was oxidized in the Fe（Ⅱ）oxidation experiment with NO3^-as the electron acceptor of P.stutzeri CQ-Z5.The reduction accounted for 28.7%of the total iron content when P.stutzeri CQ-Z5 were inoculated into a single Fe（Ⅲ）medium,suggesting P.stutzeri CQ-Z5 was an IB which can drive Fe（Ⅱ）oxidation and Fe（Ⅲ）reduction simultaneously.P.stutzeri CQ-Z5 had strong biofilm formation ability and could produce corrosive organic acids including formic acid,acetic acid,and propionic acid.In addition,we carried out bioinformatics analysis of the whole genome sequence of P.stutzeri ATCC 14405.The results showed that there were many genes involved in iron metabolism,biofilm formation,and key enzyme of organic acid synthesis in the genome.The most common type of steel in oil field transportation pipeline was 20^#carbon steel which contained a large amount of iron to support the growth of IB directly and promoted the occurrence of MIC in the pipeline.P.stutzeri CQ-Z5 was inoculated into the simulated dynamic corrosion system of oilfield produced water.The corrosion behavior of P.stutzeri CQ-Z5 to 20^#carbon steel was accomplished by the corrosion rate,the corrosion morphology,the biofilm distribution,the composition of corrosion products and the contribution rates of different corrosion types.P.stutzeri CQ-Z5 could accelerate the corrosion process.It appeared that corrosion rate increased first and then decreased with the extension of corrosion time.Many microorganisms gather on the surface of spherical corrosion products to form a dense biofilm.Severe uniform corrosion was observed on the surface and local area developed into pitting corrosion.CLSM results showed that a large number of living bacteria were colonized on the sample surface at the initial stage of corrosion,and the thickness of biofilm decreased with extending the exposure time.XRD analysis showed that the products were mainly composed of iron oxides such as Fe₂O₃,Fe₃O₄ and FeOOH,and the contribution of biofilm corrosion was greater than that of ion corrosion and organic acid corrosion.According to the corrosion behavior of P.stutzeri to 20^#carbon steel,we speculated that the corrosive ions in the initial corrosion solution eroded the carbon steel,resulting in the dissolution of a small amount of Fe（Ⅱ）.P.stutzeri CQ-Z5 grew rapidly when O₂ was sufficient,and then Fe（Ⅱ）combined with OH^-produced by cathode formed Fe（OH）₂.Fe（OH）₂ was further oxidized to Fe OOH,which dehydrated to Fe₂O₃.Biofilm was formed by P.stutzeri CQ-Z5,extracellular polymers and corrosion products.The oxygen consumption of P.stutzeri CQ-Z5 lead to the formation of oxygen-poor zone under the biofilm.P.stutzeri drive Fe（Ⅱ）under the anoxic environment of the biofilm,which accelerates the corrosion of carbon steel.The metabolites increased gradually on the cell surface,hindering the transfer of charge and nutrients,and resulting in a decrease in corrosion rate.