Study On Corrosion Behavior Of Oil Well Tube In Multivariate Thermal Fluid Environment

As the heavy oil reservoirs was increasingly discovered,their development faces really severe challenges.The country has vigorously developed a variety of thermal fluid throughput technologies and achieved significant results which increase the production of heavy oil.The corrosive gas components such as CO₂ and O₂ in the multivariate thermal fluid will cause rapid corrosion of the heat injection pipeline,which poses a challenge for the choice of the material of heat injection pipe and limits the development of the multivariate thermal fluid throughput technology.In this paper,P110 steel was used as the experimental material.The corrosion of P110steel with different Cr contents in the CO₂-O₂ coexistent environment was systematically studied by high temperature and high pressure corrosion simulation experiments,electrochemical testing techniques,and modern surface analysis techniques such as SEM,EDS,and XRD,which get the chemical behavior,corrosion product film structure and corrosion mechanism.The conclusions are as follows:?1?In the CO₂-O₂ coexistence environment,local corrosion occurred in P110 steel under different oxygen conditions.The corrosion rate gradually decreased with the decrease of oxygen content,and the pitting corrosion degree was reduced.The corrosion products mainly consist of Fe₂O₃,FeCO₃ and a small amount of FeOOH,and the content of FeCO₃ gradually increases with the decrease of oxygen content.The corrosion product film is a double-layered film structure.The outer layer is a red-brown corrosion product composed of oxide of Fe.The inner layer is composed of FeCO₃ and a small amount of FeOOH,Fe₂O₃.When the oxygen content is 5%,the grain size of ferrous carbonate inside the pit is significantly reduced.With the decrease of oxygen content,the film resistance?R_f?and charge transfer resistance?R_t?of the corrosion product gradually increase,the film capacitance?C_f?of the corrosion product decreases,and the protectivity of the corrosion product significantly improves.?2?When the content of Cr in steel is less than 5%,the corrosion morphology of P110steel shows local corrosion.With the increase of Cr content,the number of pits on the surface of the metal is significantly reduced,and the Cr content in the bottom of the pit is high.Corrosion products have reduced the grain size at the bottom of the pit,and the fine and dense grains provide a certain resistance to the longitudinal development of corrosion,forming a shallow pit-like corrosion morphology.When the Cr content in the steel reaches 5%,it becomes general corrosion.When the Cr content is less than 5%,the corrosion product on the surface of the sample mainly consists of FeCO₃,FeOOH,Fe₂O₃ and Fe-Cr solid solutions.As the Cr content increases,the film resistance?R_f?,charge transfer resistance?R_t?,linear polarization resistance?LPR?increase,the film capacitance?C_f?decreases,and the protectiveity of the corrosion product increases.As the area decreases,the increase of Cr increases the compactness of the corrosion product film and significantly enhances the corrosion resistance of the material.?3?With the increase of oxygen content,the corrosion rate of P110-5Cr steel increases,and when the oxygen content increases to 10%,local corrosion occurs,and the local corrosion degree increases as the oxygen content continues to increase.FeCO₃ and FeOOH in the corrosion products exist only under the conditions of oxygen content of 10%and 15%,while Fe₂O₃ and Fe-Cr are always present.With the increase of oxygen content,the corrosion product film of P110-5Cr steel transforms from the original single-layer film structure to the double-layered film structure with Cr-rich layer at the bottom,and then transforms into a single-layer film structure consisting of only Cr-rich layers..Cr-enriched corrosion products have significantly improved properties in terms of compactness and adhesion to the substrate.The pits of P110-5Cr steel are mostly flat-bottomed pits.The inside of pits is mainly composed of compounds of Cr and O.The outer part of pits is mainly composed of Fe,O and a small amount of Cr,and the distribution of Cr is uneven.When the compounds of Cr and O exist alone,their adhesion to the matrix and the protection to the matrix are poor.Corrosion products composed of Fe,O,Cr together have better protection to the matrix.