Study On Corrosion Mechanism And Protective Measures Of Gas Well Tubing String In Sudong Block Of Sulige Gas Field

The Sudong block of the Sulige gas field is a low-CO₂ gas reservoir,and the high mineralization of the formation water leads to a complex corrosion environment in the block.Therefore,there is a risk of CO₂ and Cl^-electrochemical corrosion in the gas well string.Some gas wells are seriously corroded and even have corrosion perforation,which brings potential safety hazards to gas field production.Therefore,corresponding anti-corrosion measures should be taken.This paper first investigates and analyzes the natural gas composition and formation water quality composition of the Sudong block in the Sulige gas field,and analyzes the main corrosion factors and the influencing laws of the pipe string in the block.Then,the corrosion rate and mechanism of the pipe string were studied by immersion test and high temperature and high pressure simulated corrosion test,and the corrosion samples were analyzed by SEM,EDS and other technical means to explore the influence of the main corrosion factors on N80,J55 and P110 steel.Then,using electrochemical workstations,the polarization curve tests of N80,J55,and P110 steels were carried out to further clarify the corrosion mechanism of the three steels.Finally,the corrosion tests of 7 typical gas wells were carried out for the two corrosion inhibitors selected in the laboratory.A set of low-cost and long-term anti-corrosion measures has been formed,which is suitable for Sudong block of Sulige gas field.The results show that Cl^-concentration is the main factor affecting the corrosion rate of the pipe string.When the Cl^-concentration is low,the product film on the surface of the sample is dense and uniform,which can protect the carbon steel substrate better.When the concentration of Cl^-increases to more than 50636.13 mg/L,Cl^-will destroy the passive corrosion product film on the surface of carbon steel,resulting in partial shedding of the product film and serious local corrosion.The five inhibitors have better water solubility and dispersibility,and superior physical and chemical properties.The corrosion process of N80,P110 and J55 pipes is mainly cathodic process,and the five corrosion inhibitors are anode type,and the corrosion inhibition rate of inhibitor A and B is higher.Under the conditions of simulating actual well conditions,after adding corrosion inhibitors A and B,the corrosion rate is significantly reduced.When the concentration is 1000 mg/L,the corrosion inhibition efficiency can reach more than 89%.Field down-hole test shows that the corrosion rate of gas wells filled with corrosion inhibitor is significantly lower than that of gas wells without corrosion inhibitor,and there is a tendency for the corrosion rate of hanging gas to increase with the increase of well depth.Corrosion inhibitor A and B can meet the anti-corrosion requirements of the block.In view of the large differences in water production,gas production and water gas ratio of gas wells in the block,the specific injection system should be adjusted properly according to the actual working conditions.