Research Tube Steels Corrosion Behavior Of Production Well In CO₂ Enhanced Oil Recovery

Because the Xinghe Chang Six reservoir formation water is weak acidic,the water contains large amounts of inorganic salts and dissolved carbon dioxide,hydrogen sulfide,as the high pressure CO2 gas is injected into the formation,CO2 will inevitably come into contact with salt water,H2S,oils,suspended solids(suspended solid,SS)and other substances to form a complex corrosive environments.This corrosive environment causes corrosion on down hole string,ground mining,collection,transportation pipeline and equipment,resulting perforations or broken in the well bore tubing and casing.There is an urgent need to combine the actual situation,to carry out research in the well bore corrosion factors,providing a basis for seeking a more effective anti-corrosion measures.In this paper,Firstly chemical volumetric method and instrumental analysis are used to analyze the composition of the water and the quality of the injected water in the Xinghe Chang Six reservoir in detail.Based on the results,the weight loss method is used in the experiment.The corrosion behavior of the commonly used tubing in different carbon dioxide pressure,salinity,temperature and other conditions were studied,and the surface of the coupon was monitored by scanning electron microscopy,energy dispersive analysis,X-ray diffraction and pitting microscopy.Morphology and corrosion products were analyzed,and the influence of corrosion products on the corrosion of steel products during carbon dioxide flooding was studied by electrochemical method.The influencing factors of wellbore corrosion of carbon dioxide flooding production well in Xinghe Chang 6 reservoir were analyzed in detail.Through the above research,(1)The type of Xinghe Chang Six formation water is CaCl,,pH change in the vicinity of 5.90?7.50,the salinity of sewage and the content of Chloride change largely,salinity is range from 6000 to 70000mg/L,the content of Chloride is range from 3000 to 40000mg/L,calcium ion content is between 700?10000mg/L,Magnesium ions content of 30?900mg/L,the water quality has the tendency of corrosion and fouling.(2)For N80 and J55 materials,the gas phase corrosion is relatively low,and the liquid phase corrosion is high;in the range of CO2 pressure 0-25MPa,the corrosion of N80 material in gas phase and liquid phase first increases and then decreases and last increases.The(3)gas-phase corrosion rate reaches the maximum at 3MPa,and liquid-phase reaches the maximum at 2MPa.The corrosion rate of the gas phase and the liquid phase is fluctuating in the range of 0 to 10MPa,but on the whole,the gas phase corrosion rate first increase then decreases and last increases,the liquid phase showed a trend of increasing first and then decreasing.For the gas phase and liquid phase corrosion rate,the maximum value appeared at 8MPa.The two materials are mainly due to the increase of carbon dioxide solubility and corrosion product film ferric carbide and ferric carbonate,making the corrosion appear the above-mentioned rule.(4)With the increase of mineralization,the gas-phase and liquid-phase corrosion rate of N80 material first increases and then decreases,and J55 material gas phase and liquid phase corrosion first decreases and then increases.And HCO3-together with Cl-,making the corrosion of the above rules.(5)Whether the J55 or N80 material,when there is CO2,the corrosion of the coupon after the surface is not smooth,local corrosion occurs,the surface of the loose crystal products covered,the white crystals may be scaling products and corrosion products.The EDS analysis of the corrosion product film on the surface of the coupon shows that the product film contains mainly C,O,Na,Cl,Ca,Mn,Fe and other elements.Mn,Fe elements should come from the base metal,Na,Ca and Cl elements should come from the simulated oilfield sewage crystallization of inorganic salts.Fe,C,0 and other elements are high,the main components of corrosion products are FeCO3 and Fe2O3.(6)Whether the pressure increases,the salinity increases or the temperature increases,the distribution of pitting pits tends to increase,and the corrosion of the coupon is mainly from the local corrosion to the uniform corrosion.The corrosion resistance of J55 is better than N80 under high carbon dioxide pressure,and the corrosion resistance of carbon steel is better than t J55 under high carbon dioxide pressure,and the corrosion resistance of J55 is better than that of N80 at 80 ?.(7)Through the study of electrochemical method of J55 material corrosion,carbon dioxide corrosion is controlled by the cathode corrosion.