Study On Corrosion Behavior Of Nickel-based Alloy In Harsh Oil And Gas Well Environment

With the increasing demand for oil and gas resources,some deep wells and even ultra-deep wells have been continuously developed.The temperature,pressure,CO2 partial pressure and Cl^-concentration faced by the downhole pipe string are getting higher and higher,and the service environment is becoming more and more demanding.It is urgent to choose a nickel-based alloy with better corrosion resistance.In this paper,the physical and chemical properties test,high temperature weightlessness test,electrochemical test analysis and stress corrosion cracking test methods,supplemented by modern analysis techniques such as SEM,EDS and XPS,were used to study the corrosion of 028 nickel-based alloys in the harsh corrosive environment underground Behavior,and analyze its corrosion law and corrosion resistance mechanism.The main conclusions of the paper are as follows:?1?In a high-temperature CO₂ corrosion environment,the maximum corrosion rate of028 nickel-based alloy is only 0.0041mm/a,no local corrosion signs appear,and it shows extremely excellent high-temperature CO₂ corrosion resistance.Its good corrosion resistance comes from Cr element enriches the Cr2O3 passivation film formed on its surface;under fresh acid corrosion conditions,the corrosion rate of 028 nickel-based alloy is relatively high,but it is still within the first-level range specified by the standard,and the residual acid and acidization completion process In the test,the deeper the well,the greater the corrosion rate of the 028 nickel-based alloy.During the completion of the fresh acid,residual acid and acidification,the samples all show obvious pitting pits,and the maximum pitting depth varies with temperature and temperature.The increase in CO₂ partial pressure shows an upward trend;in the corrosion environment of the completion fluid,its uniform corrosion rate increases significantly with increasing temperature.In the ultra-high temperature CO₂ environment,the C ring sample did not break,the stress corrosion sensitivity was low,and the resistance to stress corrosion was good in the high temperature CO2 environment.?2?The results of electrochemical tests show that in a high-temperature CO₂environment,with increasing temperature,the corrosion potential of the polarization curve decreases and the self-corrosion current density increases,the corrosion driving force increases,the protective effect of the passivation film weakens,and the high-frequency region The radius of the capacitive arc is getting smaller and smaller,the polarization resistance is reduced,and the corrosion rate is increased.In the completion fluid environment,the 028 nickel-based alloy anode polarization curve has obvious passivation areas,and the corrosion reaction is controlled by the anode reaction process.As the temperature increases,the corrosion potential decreases,and the corrosion process significantly intensifies.In the corrosive environment of high-temperature CO₂ formation water and completion fluid,as the temperature increases,the capacitance arc radius of 028nickel-based alloy decreases,and the polarization resistance shows a downward trend,but the value of polarization resistance is still very large,with good corrosion resistance.?3?XPS sputtering on the surface of the sample after corrosion under severe conditions shows that the passivation film after 028 nickel-based alloy corrosion is a bipolar film,and the passivation film mainly consists of oxides and hydroxides of Ni and Cr Pose.The hydroxide film formed after corrosion can hinder the diffusion of anions to the inner layer of the passivation film,and the oxide film can prevent the diffusion of cations to the outside of the passivation film,thereby protecting the base metal,and the passivation film has a strong self-repairing ability.