Research On Corrosion Mechanism Of Gas Well In Y Block And Evaluation Of Corrosion Inhibitor Application

Gas reservoirs in Y block of Western Sichuan are deeply buried with formation pressure up to 80MPa.The produced gas generally contains CO2 and has high partial pressure.In addition,the formation water production and salinity of formation water increase in the later stage of production.The corrosion of underground pipe string is serious in harsh production environment.Class P110 tubing and casing steel is the main material used in downhole tubing string in this area.P110 steel belongs to common carbon steel with general CO2 corrosion resistance.During its use,multi-well corrosion perforation occurs,which seriously restricts the safe production of gas fields.Therefore,studying the corrosion mechanism of P110 steel in the production environment of Y block,summarizing the influence rules of various factors on corrosion behavior,optimizing the corrosion inhibitors suitable for this block,and putting forward a set of scientific injection methods of corrosion inhibitors have important practical significance for stable production and high production of Y block gas field.On the basis of investigating the field corrosion data of West Sichuan Gas Field,the components of gas,formation water and corrosion products collected in the field were analyzed by means of gas chromatography,ion chromatography,XRD and SEM,and the main causes of P110 tubing corrosion in Y block were studied.The influence of various corrosion factors on P110 tubing was studied by using high temperature and high pressure reactor,which provided a direction for the optimization of corrosion inhibitors.Three target corrosion inhibitors were evaluated under simulated production conditions,and CX-19 corrosion inhibitor was selected as the corrosion inhibitor for field use.On this basis,CX-19 corrosion inhibitor filling experiment was carried out,and the reasonable filling speed and period of corrosion inhibitor were determined.The main conclusions are as follows:(1)The produced gas in Y block gas reservoir generally contains CO2 and does not contains H2S gas.CaC12 is the main type of formation water.The concentration of Cl-is between 30000 and 70000 mg/L.The salinity of formation water is high and the corrosion of underground pipe string is serious.The corrosion products are mainly iron and calcium compounds,iron mainly exists in the form of FeCO3,and calcium mainly in the form of calcium carbonate and calcium magnesium carbonate.It is concluded that the corrosion of downhole pipe string in Y block is mainly caused by CO2,Cl-and high salinity formation water.(2)When no inhibitor was added,the pitting corrosion of P110 was serious,and the average annual corrosion rate was 2.89mm·a-1.After adding CX-19 inhibitor with 1.0%mass concentration,a thick black protective film was formed on the surface of the specimens.The corrosion rate was reduced to 0.3 8mm a-1 and the inhibition rate was 86.73%.After cleaning the test piece,it was found that there were slight pitting marks on the surface of P110,the pitting area was evenly distributed,the pitting pit depth was shallow and close to uniform corrosion.The corrosion inhibitor could effectively avoid the corrosion perforation of the tubing,so CX-19 was chosen as the corrosion inhibitor used in the field.(3)Under simulated production conditions,the maximum injection flow rate of corrosion inhibitor without effusion is 8.6L/min,which is used as the maximum injection rate of corrosion inhibitor.Fluent was used to study the film quality of CX-19 corrosion inhibitor.It was found that the film was formed near the injection wellbore after the corrosion inhibitor was injected into the wellbore.After the corrosion inhibitor was continuously injected for 6000s,the liquid film of the whole circumferential section became uniform,and the thickness basically remained 2.5mm.The thickness of the inhibitor film is about 1.0 mm after 5 days of stopping the injection of the inhibitor,and there is no area where the inhibitor film is destroyed.After 7 days of stopping the injection,the inhibitor film is partly destroyed and the pipe wall is exposed to the corrosive medium.Therefore,the batch injection period of the inhibitor is determined to be 5 days.