Study On The Influence Of Trace Amounts Of H₂S On CO₂ Corrosion Behavior Of Low Cr Tubing Steel

H₂S and CO₂ casing corrosion is an important risk factor for oilfield production and development,which also greatly increases the production cost of oilfield.At present,the research of domestic and foreign scholars on the coexistence environment of H₂S and CO₂ are thorough.The corrosion mechanism of carbon steel at the trace amounts of H₂S is also generally recognized,but the research of the low Cr steel in CO₂ corrosion environment with trace amounts of H₂S is less.The lower limit of risk concentration for pitting corrosion of low Cr steel induced by H₂S is not clear,and further study urgently needed.In this paper,H₂S and CO₂ gas dissolved in aqueous solution will form an acid solution and corrode the tubing steel.The relationship model between the concentration of ions and the partial pressure of CO₂/H₂S corrosion gas obtained by calculating the equilibrium of dissolution and ionization in thermodynamics.Due to the high toxicity hazard of H₂S gas,a set of experimental process was designed to prepare low concentration H₂S and the reactive gas,and the dosage relationship of solute needed to prepare the trace amounts of H₂S was determined.Combined with relevant corrosion theories,N80 carbon steel and 13Cr steel were used as the control group in the experiment to study the influence mechanism and rule of low Cr steel in the CO₂corrosion environment with trace amounts of H₂S,and the lower limit of H₂S concentration for pitting corrosion was determined.Although the Cr content of low Cr steel is between N80 carbon steel and 13Cr steel,the most serious pitting behavior occurred in low Cr steel.Considering the influence of the microstructure of the tubing steel on corrosion,it is found that the corrosion characteristics of the experimental steel after different heat treatment are quite different,which is mainly related to the defect of the crystal structure.The crystal structure defects of microstructure were induced and enlarged by the trace amounts of H₂S,which provided theoretical basis for the engineering application of low Cr tubing steel.