Study On Corrosion Behavior Of Switch Material And Synergistic Effect Of Encapsulated Corrosion Inhibitor

In oilfield downhole, inhibitors have been widely used to inhibit CO2 corrosion from the aggressive environment induced by high temperature, high pressure, high salt and a large amount of CO2. Although this method is low-cost, there are still some problems, for example corrosion inhibitor may fail to reach the bottom of the oilwell, low utilization efficiency of corrosion inhibitor. Aiming at this problem, this work provides a new device for controlled release of oilfield corrosion inhibitor based on electrochemical principle to realize long-term protection of downhole equipments. The device consists of electrochemical encapsulation switch, packaging container, weighting agent and corrosion inhibitor.Firstly, potentiodynamic polarization curves and weight-loss experiment are adopted to investigate the influence of inhibitor concentration and ratio of cathodic to anodic area on corrosion rule of switch materials. Results show that with the increase of inhibitor concentration, galvanic anodes in A3 carbon/magnesium alloy and A3 carbon steel/zinc alloy couples are characterized by uniform corrosion. Corrosion inhibitor concentration has a little influence on anodic corrosion rate. Corrosion rates of magnesium and zinc anode are about 950 and 7.0 mm/a, respectively. Galvanic anode in A3 carbon steel/aluminum alloy couple exhibits the characteristics of local corrosion. These three galvanic couples show the corrosion promotion effect in pure inhibitor. Besides, with the increase of area ratio of cathodic to anodic, anode corrosion rates increase, and there is a linear relationship between corrosion rate and area ratio. Corrosion rate of magnesium anode increases from 775 mm/a to 1033 mm/a with the increase of area ratio from 5 to 20. Corrosion rate of zinc anode increases from 5.6 mm/a to 12.8 mm/a.Secondly, potentiodynamic polarization curves and EIS test were used to study synergistic effect of zinc chloride weighting agent and pyridine inhibitor on downhole equipment. Results show that when the mixing ratio of pyridine inhibitor to zinc chloride is less then 400, the inhibitors show good synergistic effect, which greatly improves the anti-corrosion effect. The inhibitive efficiency increases from 51.36% with pyridine inhibitor only to 84.56% with added 2000 mg/L of zinc chloride. At the same time, the method reduces the amount of pyridine inhibitor and improves utilization efficiency of zinc chlorine.