Gas Storage Column Fatigue Life Prediction Of Corrosion And Mechanical Interaction

With the increase of domestic gas demand, the depleted reservoirs of gas storage is widely used in natural gas storage,however, in the process of operation will appear all sorts of security risks, especially injection-production well.Gas storage injection production wells,in the underground complex environment, will be subject to joint action of corrosive gases and alternating loads, promote each other, thereby greatly reducing the life of the column. At present, the corrosion behavior of depleted reservoirs gas storage is not clear, and there is no consideration of corrosion and mechanical work together to the string life influence, predict string service life.Therefore, monitoring, anticorrosive and life prediction of injection-production wells have become a subject that must be studied in advance.In this thesis,the gas storage in wen 96 was selected as researed object, study of the corrosion rule of gas storage tube column, analyze the stress of pipe string, combined with the corrosion rate and the three axis stress, establish the prediction model of fatigue life of pipe string, and predict the service life of gas storage.The main conclusions are as follows:(1)Corrosion of tube and column is mainly based on electrochemical corrosion and erosion corrosion.Electrochemical corrosion is caused by CO2 and H2 O,Corroded areas at1900 m above,the corrosion morphology of uniform corrosion and pitting corrosion,Erosion occurred in the gas recovery period and gas injection period, the safety valve and the slip cover first occurred erosion. Gas recovery period, when the wellhead pressure is 5MPa, the amount of gas more than 29.0×104m3/d will appear erosion, gas injection period, when the wellhead pressure is 20 MPa, the amount of gas more than 70.22×104m3/d will appear erosion(2)According to the field coupon monitoring results: two stage monitoring,Wen96-13 well and Wen96-8 well of three kinds of material in the gas phase corrosion speed is less than0.25 mm/a, belonging to slight corrosion, and the corrosion rate of the first two monitoring compared with the first one to increase the number of times;The first stage is gas injection stage, the second stage contains gas injection-production,the safety valve and the slip cover first occurred erosion.(3)The internal pressure and the external force are converted into axial force,calculating the axial force of the gas storage tube.And give casing under the triaxial stress formula of strength of pipe body, combining with triaxial stress and corrosion rate, launch string corrosion life prediction formula, calculate the string collapsing life of 10.57 years,tensile life expectancy of 6.21 years.(4)According to the formula of pipe thread checking, the fatigue life prediction formula of gas storage cylinder under the combined action of corrosion and mechanics is established,and the service life of the gas storage tube column is 36 years. On the basis of this, it puts forward the measures to prolong the service life of the gas storage cylinder.