Evaluation Method Of Tubing Integrity Of Offshore Gas Well

The issues of sustained casing pressure in offshore gas well caused by tubing failure is increasingly outstanding,which is a serious threat to production safety.Analyzing tubing integrity and researching integrity detection and evaluation methods of tubing in service can perfect the tubing integrity theory and improve quantitative evaluation technology for service status.The research can provide technical support for gas well integrity management and ensuring the safety of offshore gas well.To this end,the following research work were completed.(1)Tubing integrity concept was proposed by introducing concepts of physical integrity and structural integrity.Tubing failure modes of physical integrity and structural integrity were analyzed.Monitoring parameters of tubing physical integrity failure was researched.In terms of people,equipment and environment,the evaluation index system of gas well tubing integrity was established.(2)A series of tubing manual defects detection experiments were conducted in laboratory by using magnetic memory detection technology.The relationship between holes and slotings defect size and magnetic memory detection signal were researched,which provided basis for the inversion calculation of tubing defect size and location and the characterization of the structural integrity of tubing degradation state.(3)The stress condition of tubing in service was analyzed by taking production string structure,production environment and hole structure of offshore gas well with sustained caing pressure into consideration.Aimed at the different locations where the paker was,vertical interval or deflecting interval,calculation models of axial force and stress were established,which provide calculation method to determined tubing forced status.(4)The Von mises equivalent stress of tubing with uniform corrosion defects and pitting corrosion defects was calculated by using finite element method.The relationships between the Von mises equivalent stress of tubing and defect size and load were analyzed.The main influence factors for the tubing equivalent stress were determined.The functions for calculating the Von mises equivalent stress of corroded tubing were fitting based on simulation results.The verification of the fitting results showed that the average error between the original calculation data and the fitting calculation data are 2.95% and 1.99%.Fitting formula can be used to calculate the Von mises equivalent stress of tubing.(5)Integrity assessment software for offshore gas well tubing was developed.Magnetic memory testing data processing and analysis,tubing stress calculation and tubing integrity parametric evaluation were achieved.The software provided support for field applicationBased on the research,a set of integrity evaluation method for offshore gas well tubing was established,which provides technical support for tubing integrity management.