Analysis Of The Genesis Of Sulfur And Control Of Microbial Corrosion In Oilfield Water System

Sulfate reducing bacteria （SRB） is one of the main reason have caused differentcorrosion in oilfield which constantly caused pitting corrosion in the sewage system. Thereason is that Chemoautotrophic SRB can revert sulfuric acid to elemental sulfur andsulfide to accelerate the corrosion. At present, the sulfide content in most oilfield wastewater has reached between45⁵5mg/L which delays the safe drilling process and coststoo much. This paper will systematic study the reason of the oil well sulfide during water-flooding the jiangsu oilfield, the main factors caused corrosion in SRB and sulfidecoexistent system, the abilities of antibacterial performance tests and electrochemicalevaluation technologies of the fungicide on biological membrane, and by wire beamelectrode on-line monitoring potential current changes when it exists fungicide underbiofilm. The research results have great significance to safe and efficient production.Some analytical methods （isotope tracer technique、XRF、SEM and fluorescencemicroscopic imaging）were applied to analysis the water quality of oilfield sewage、thereason of formation of hydrogen sulfide、the relationship between SRB and sulfide and itscorresponding relation and the growth of83SRB. The results showed that the corrosion arecaused by high content of SRB and sulfide, high formation water salinity in oil Wells, andthe water was the typical NaHCO₃type. In addition, the sulfide was mainly caused bysulfuric acid of reduction through SRB and positively related with SRB content as theextension of detection time. The83SRB was classified as desulfotomaculum, the optimalgrowth temperature was37℃, the optimum pH was6, and it could grow up in widetemperature and big PH value scope.Besides, the corrosion of20#steel materials in the produced water system wassurveyed under different sulfide concentration conditions by using orthogonal designprinciple to understand the damage and synergetic action of sulfide and the microbialcorrosion. The results showed that the20#steel corrosion rate increased with the rise oftemperature and was more serious than without SRB. When it was70℃, the major effectof the corrosion depended on the water quality factors. What ‘s more, when the solution ofsalinity was low, the corrosion rate of steel20#as the solution was inversely proportional to the salinity; when the solution of salinity increased to a certain value, the corrosion ratereached the maximum and then dropped rapidly. The effect of various ions on20#carbonsteel corrosion was Cl> S²> SO₄^2-.Some analytical methods were applied to study the antibacterial properties ofbactericides and the toxicity of bactericide by diluting extinction method、corrosionpotential method、EIS and polarization curve method. The results showed that the LC-3andBardac had strong antibacterial properties to the suspension of83SRB, the minimuminhibitary concentration were100mg/L and40mg/L respectively. For83SRB underbiofilm,the minimum inhibitary concentration were140mg/L and70mg/L respectively,and the bacterial inhibition under the film more thorough with the fungicide concentration.The bactericidal effect of Bardac was better than LC-3. when in high SRB content, thefungicide of SRB in the biofilm inhibition was very limited, which LC-3dosing400mg/Land bardac dosing240mg/L the inhibition of bacteria in the biofilm were2days and5days respectively. The Biofilm growth law study had shown that83SRB had certain cycleof growth and peeling off in the material surface,it began to form biological membrane onthe4th day and grew gradually completed on the9th day until damaged or fell off on the14th day. When adding bardac in sewage, it firstly reduced the density of free SRB to movecorrosion potential. Then after contacting with biofilm, bacteria continuously penetratedinto the biofilm by adsorption and inhibited bacterial respiratory so that kill membranebacteria. Antimicrobial coverage slowly increasing until on the14th day efficacy wasslowly reduced and declined gradually.