Galvanic Corrosion Research Of Production Tubing, Production Casing And Packer Materials In Packer Fluid

In this paper, the materials of typical production tubing, production casing and packer in sour oil and gas wells were taken as the experimental materials, then the galvanic corrosion behaviors of Inconel 718-VM80SS couple and N08028-BG95SS couple in packer fluid system were investigated by electrochemical method and immersion experiment method. The Data gained by these two methods were . compared and discussed. On the other hand, the effect of galvanic potential, cathode/anode area ratio and the distance between coupled steels on the galvanic corrosion behaviors of these two couples were researched. It was consulted as reference for improving life of these steels. Throught series of tests and analysis, the conclusions is reached as follows:It was oxygon depolarization corrosion of these steels in the packer fluid system according to the theoretical analysis and corrosion products' EDS analysis. Corrosion potential of VM80SS was lower than that of Inconel 718 and BG95SS was lower than that of N08028 in packer fluid. In Inconel 718-VM80SS couple, VM80SS acted as the anode and the corrosion rate increased, Inconel 718 acted as the cathode to be protected, and in N08028-BG95SS couple, BG95SS acted as the anode and the corrosion rate increased, N08028 acted as cathode to be protected.The dissolution current of VM80SS and BG9SS got by immersion experiment method was as 1-10 times as the galvanic current got by ZRA method, and the value of the multiple increases as the area ratio. According to the theoretical analysis and previous reseaches, the cause of this phenomenon might be the existence of micro-batteries on the surface of the anode VM80SS and BG9SS, i.e. not only the anode dissolution was taking place, but also the cathode process was acting rapidly.Galvanic effect of the two couples increases as the area ratio, and relationship between galvanic potential and cathode/anode area ratio accorded with the rule of logarithm, when galvanic current density and cathode/anode area ratio accorded with the rule of linearity.The interval of galvanic potential from the cathode to the anode was only 60mV for Inconel 718-VM80SS couple and 50mV for N08028-BG95SS couple and galvanic current and corrosion rate were both tiny when cathode/anode area ratio was less than 3 (when cathode/anode area ratio equal to 3, corrosion rates of VM80SS and BG95SS were 0.033mmpy and 0.028mmpy respectively), so the galvanic corrosion trend was not serious in this system. But to avoid large cathode/anode area ratio was indispensable in practical project according to the linear rule of galvanic current density and cathode/anode area ratio.Combined with the characteristics of oil and gas wells, galvanic corrosion can be inhibited from taking methods such as reasonable design, reasonable selection of materials, surface treatment, insulation and addition of corrosion inhibitors according to our research results and correlative research in the field of spaceflight and navigation.