Role Of Pseudomonas Fluorescens Digesting Oil On Corrosion Inhibition Behavior Of Q235b Carbon Steel In Oilfield Produced Water

Nowadays,corrosion has become an important issue in oilfield production.Corrosion represents a considerable economic stake projected between 1 and 4%of the gross national product?GNP?of developed countries.Carbon steel is one of the most widely used pipeline materials in the oil and gas industry.Solving the problem of carbon steel corrosion will greatly reduce the economic loss of the oil industry.Traditional anticorrosion methods are costly or may cause secondary pollution.Microbiologically influenced corrosion inhibition?MICI?is a new green anti-corrosion technology.Researchers have discovered a number of microorganisms that can inhibit metal corrosion and explore their mechanism of inhibiting metal corrosion.In this paper,a strain of Pseudomonas fluorescens was screened,which could not only inhibite the corrosion of carbon steel,but also digest crude oil and avoid pipeline blockage.The main conclusions are as follows:?1?The p H value of oilfield produced water in the No.5 Oil Production Plant?Dingbian?Oilfield of Changqing Oilfield is 5.23 weakly acidic,and the organic matter concentration is2408 mg/L.In addition,the salt content of oilfield produced water is very high,which may be an important cause of pipeline corrosion.?2?The oil field produced water and crude oil mud were mixed uniformly,and the strains were separated by coating plate method and plate streaking method after gradient dilution,and 23 strains were isolated after microscopic examination.Four strains that can inhibit the corrosion of Q235B carbon steel were screened by corrosion weight loss method and Tafel curve method,which were Bacillus cereus,Pseudomonas fluorescens,Rhodococcus erythropolis,and Arthrobacter humicola.Many studies have shown that Pseudomonas fluorescens can slow down metal corrosion,and Pseudomonas is an oil-degrading bacterium.Pseudomonas has played a prominent role in oil and alkane biodegradation studies as all lineages of the Pseudomonas contain alkane-degrading species.Therefore,Pseudomonas fluorescens was selected for subsequent experiments.The strain is now cultured at China Center for Type Culture Collection?CCTCC?and named Pseudomonas fluorescens FSYZ01.It was determined that the crude oil degradation rate of this strain was 61.07%.?3?Carbon steel coupons were immersed in water,LB medium,and oilfield produced water for 13 days,and the thickness of the corrosion products on the surface of the carbon steel coupons was measured with an optical microscope.The results showed that the thickness of the corrosion products with bacteria was thinner than that without bacteria,and the thicknesses were decreased from 198?m,59?m,106?m to 122?m,34?m,87?m,respectively.The macro and micro morphology of the carbon steel coupons showed that the degree of corrosion of the carbon steel coupons with bacteria was lighter than that without bacteria.Besids,the LB medium also showed a good ability to inhibit corrosion.The result of weight loss method showed that the weight loss of carbon steel coupon with bacteria immersed in different working conditions for 13 days was reduced by 32.23%,54.07%,78.34%,respectively.The results of the corrosion potential measurement showed that the potentials in the three corrosive environments all moved forward after inoculation.Among them,the corrosion potential of the carbon steel in the oilfield produced water was moving most,meaning the inhibition effect was the most obvious.The result of XRD showed that the addition of Pseudomonas fluorescens FSYZ01 consumed O₂ through respiration and prevented further oxidation of iron oxides.The result of FT-IR showed that the bacteria inhibited corrosion by combining—C=O—,—COO—,—C-OH functional groups with Fe?II/III?ions to form a"chelate-oxide barriers".The result of XPS showed that the addition of the bacteria not only reduced the concentration of organic matter in the oilfield produced water,but also acted as a physical barrier with corrosion products blocking oxygen from approaching the metal surface.The result of Py-GCMS showed that the bacteria had a good ability to degrade C₁₂ to C₂₀ alkanes in the oil.?4?Mechanism of Pseudomonas fluorescens FSYZ01 inhibiting carbon steel corrosion:Pseudomonas fluorescens FSYZ01 consumed oxygen through respiration,reducing the concentration of oxygen on the metal surface;The biofilm of Pseudomonas fluorescens FSYZ01 adsorbed on the metal surface to form a biofilm barrier,which blocked the contact of oxygen with the metal surface;Pseudomonas fluorescens FSYZ01 binded with Fe ions through—C=O—,—COO—,—C-OH functional groups,and formed self-assembled monolayers through chemisorption to protect metals.