The Study On Mechanical Behavior Of Tubing String In The "Three-ultra" Oil And Gas Well

The study on the mechanical behavior of the tubing string of the "three-ultra" oil and gas well can prolong the service life of the tubing string.In this paper,based on the research and analysis of a large number of domestic and foreign literatures and the oilfield data of the ultra-deep gas wells in tarim oilfield,the research on the mechanism of the buckling behavior of tubing string,the vibration behavior during the gas recovery and the stress distribution of the tubing thread are studied.The purpose is in order to predict the mechanical behavior of tubing string during work and damage status,for our country’s "three-ultra" oil and gas well tubing string design and use of the methods provide feasible analysis method and the theory of quantitative data,and to avoid loss and damage of the tubing string failure.The main achievements of this thesis are as follows:(1)Based on a large number of domestic and foreign literatures and classical theoretical formulae derived from predecessors,a mathematical model of deformation of tubing with packer under five effects(piston effect,swelling effect,friction effect,temperature effect,spiral buckling effect)is established.(2)The finite element model of tubing string buckling and contact problem analysis of the whole well section of ultra-deep gas well is established,which can fully and quantitatively analyze the buckling morphology of the tubing string in deep wells.The feasible analysis method and quantitative theoretical data are presented for the buckling form of tubing string,failure analysis of friction damage and its preventive measures.(3)The finite element models of the original tubing string and the improved tubing string are established.The transverse modes and natural frequencies of the first 15 stage of the tubing string are analyzed,and the feasible data are provided for the prevention of resonance and prediction of vibration mode.(4)The transient dynamic finite element model of the original tubing string and the improved tubing string are established,based on the APDL program of ANSYS.The dynamic axial force,Von Mises stress,triaxial safety coefficient and buckling form of the tubing string in the whole well section,as well as the longitudinal vibration displacement of the locations near the neutral point,the velocity,acceleration,and axial force are analyzed.The vibration characteristics of tubing string structures are compared,and a feasible analysis method is provided to optimize the structure design of tubing string.(5)The axisymmetric finite element mechanical model of three types of tubing threads is established.The results show that the the thread buckle root is easy to stress concentration under the influence of inner pressure,outer pressure and axial force,it is found that the measures can improve safety factor and prevent plastic deformation of the tubing thread by improving the steel grade,which can provide the basis for the tubing thread on oilfield.