超深井气举管柱力学动态响应及失效风险评价OA

Ultra-deep wells are typically in the environments with high temperature,high pressure,and high concentrations of corrosive media such as hydrogen sulfide and carbon dioxide.During long-term service,casings are subjected to varying degrees of corrosion damage.The gas lift process,due to the coupling effects of temperature and pressure fluctuations with corrosion damage,can easily lead to the failure of tubing and casing strings.Therefore,it is necessary to establish a set of safety evaluation methods for pipe strings that consider transient multiphase flow pressures,corrosion defects,and nonlinear mechanical behaviors comprehensively.In this paper,a transient multiphase flow model of gas lift is developed using the finite volume method.The model involves gas lift flow patterns,wellbore geometry,fluid parameters,and packer leakage.Then,a three-dimensional mechanical model of corroded casing based on risk point pressure distribution is constructed by means of the nonlinear finite element method.On this basis,the safety evaluation charts for corroded casings during gas lift operations are developed.Finally,a systematic risk assessment method is constructed on the basis of annular dynamic pressure.The following results are obtained.First,during gas injection initiation and the gas lift process,the maximum annular pressure appears at a position above the packer(6 213.78 m),reaching 86.5 MPa.After gas injection stops,the maximum annular pressure transfers to the tubing shoe(6 401.9 m),and it is 83.4 MPa(with incomplete liquid unloading)and 60.9 MPa(with complete liquid unloading).Second,when the corrosion radius is 0.5-4.5 mm and the annular pressure is 55-110 MPa,the increase in corrosion radius and annular pressure at 156℃ can elevate the safety risk of H140 casing,with annular pressure having a more pronounced impact.During actual operations,therefore,monitoring focus should be put on the fluctuation of annular pressure.Third,the developed safety evaluation charts and risk assessment method can effectively evaluate the safety factors of in-service corroded casings under different gas lift stages and varying degrees of in-situ stress attenuation.The research findings provide a theoretical basis for optimizing process parameters and assessing pipe string risks during gas lift operations in ultra-deep wells.