Study On Corrosion Law Of Tubing And Casing In EOR-CCUS System

The technology that captures carbon dioxide?CO₂?from emission sources for enhance oil recovery and permanent geological storage at same time is called EOR-CCUS.When captured CO₂ is injected into the reservoir,the presence of acidic gas from emission sources and formation water will lead to the formation of strong acid,which can result in serious corrosion of production wells.The study of the corrosion law of this system is helpful to solve practical engineering problems.There will be large amount of water in the reservoir during the application of CCUS since it is usually used as a tertiary oil recovery technology.The supercritical CO₂-saturated water phase?AP?will appear in the wellbore,and the water-saturated supercritical CO₂ phase?SP?will form owing to the CO₂ solubility change with the change of well depth.In this study,autoclave was used to simulate the severe corrosion environment.Corrosion behaviors of N80 steel in two phases were studied and the main topic of this paper is the study on severer corrosion in aqueous phase.The corrosion behavior and mechanism of N80 steel were investigated by weight-loss method,surface analysis method and electrochemical method.The uniform corrosion rate was obtained by weight-loss method;The corrosion morphology characteristics were studied by scanning electron microscopy?SEM?and 3-dimensional?3D?profilometer,and the localized corrosion characteristics were analyzed to obtain the penetration rate;The chemical composition of corrosion products was detected by energy-dispersive X-ray spectroscopy?EDS?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?;The polarization curve,electrochemical impedance spectroscopy?EIS?and linear polarization resistance?LPR?were applied to understand the corrosion mechanism.The following four aspects are studied:?1?This paper studied the corrosion rate of N80 steel under the condition of high CO₂ partial pressure?8,10,12,14 MPa?.The concentrations of corrosive species in corrosive environment were calculated.The reasons for the great difference of corrosion rates in SP and AP are discussed.The results of XRD showed that there were Fe CO₃crystals in AP which might result in the reduction of corrosion rate.?2?The effect of SO₂ on the corrosion behavior of N80 steel in SP and AP was studied.The corrosion inhibition phenomenon of SO₂ impurity in AP was found.The result was quite different from those generally believed that the presence of SO₂impurity can promote corrosion.The experimental results showed that the corrosion product film in AP was stable and had high bonding strength with the matrix,which was consist of Fe S and Fe S₂.The reason of inhibition effect of SO₂ on the corrosion in AP is that the corrosion product films formed in AP had a strong protectiveness to steel matrix.?3?The influences of monoethanolamine?MEA?,diethanolamine?DEA?and N-methyl diethanolamine?MDEA?on corrosion behavior of N80 steel in SP and AP containing impurity gases?SO₂,NO₂ and O₂?were studied.The results of weight-loss measurements showed that all tested alkanolamines have corrosion inhibition effect.The corrosion inhibition mechanisms of MEA,DEA and MDEA in CO₂ corrosion environment were investigated by electrochemical experiments,and the neutralization and adsorption effects of MEA,DEA and MDEA were proved.?4?The corrosion inhibition effects of imidazoline and piperazine on N80 steel in SP and AP containing impurity gases?SO₂,NO₂ and O₂?were studied.The results showed that when the concentration of piperazine is 1000 ppmv,the corrosion inhibition efficiency of piperazine in AP reached 86%.Severe localized corrosion was observed in both SP and AP with the existence of imidazoline.These results showed that the corrosion inhibitors commonly used in oil and gas fields may not be suitable for EOR-CCUS systems.