Study On The Application Of Imidazoline CO₂ Corrosion Inhibitor In Oil Wells

Many large oil fields in China used CO₂ flooding technology to enhance oil recovery. But significant amounts of CO₂ existed in the process can cause severe corrosion and failure of oil well downhole equipment. It is remarkably effective to control the CO₂ corrosion by using corrosion inhibitor, but the corrosion inhibitor strongly depends on the environment. And the performance of the corrosion inhibitor should be evaluated according to the actual corrosion environment before be applied for field. Also, the diffusion rule should be studied under the dynamic condition of oil production.The underground working environment was simulated by laboratory autoclave under high pressure and high temperature. The influences of corrosion inhibitor performance, such as dosage, gas-liquid ratio, were investigated. The results showed that when the dosage reached 150 ppm, with the increase of dosage, it had little effect on the performance of corrosion inhibitors. Along with the increase of gas-liquid ratio, the corrosion rate of N80 steel was increased. After adding corrosion inhibitor, inhibition efficiency was higher than 80%, and the corrosion rate was reduced to below 0.5 mm/a. It illustrated that CO₂ corrosion inhibitors could still work well under the environment of high temperature and high pressure in the field.The extraction process of oil well produced fluid was simulated by the oil well simulator. The influences of diffusion behavior of corrosion inhibitor in the wellbore, such as the thickness of the oil, the concentration of corrosion inhibitor, velocity of flow and moisture content, were investigated. The results showed that the diffusion time of corrosion inhibitor in the oil had a linear relation with the thickness of the oil basically. And the diffusion velocity of corrosion inhibitor in the oil cap was about 96 m/d. Under the dynamic condition, the influence of filling corrosion inhibitor concentration had two sides. With the increase of concentration of corrosion inhibitor, on the one hand the overall inhibitor efficiency increased, on the other hand the uniformity of the diffusion of corrosion inhibitor declined. From the comprehensive analysis, when the concentration of corrosion inhibitor filling is 750 ppm, the effect was better. With the increase of velocity of flow, the overall inhibitor efficiency was decreased, but the distribution of inhibitor efficiency of corrosion inhibitor was more gently. That showed the uniformity of the diffusion of corrosion inhibitor was still good under the condition of high velocity. In well produced fluid of high water content stage, moisture content had litter effect on the diffusion velocity of the corrosion inhibitor.Regarding an oil well from the oil production plant from as the research target, filling corrosion inhibitor of scene in oil was investigated. The results showed that without corrosion inhibitor, the content of Fe2+ in produced fluid was 34.2 mg/L. With the addition of corrosion inhibitor, the content of Fe2+exhibited decrease first and then increase. When 3 days later, it showed a significant decline and the content of Fe2+ was 9.3 mg/L. When it filled 12 days, the content of Fe2+ was 27.8 mg/L. The results indicated that the time of corrosion inhibitor diffused to the bottom was 2 days. And one-time filling the duration of the corrosion inhibitor was about 10 days.