Study On Mechanical Behavior And Optimization Design Of Tubing String In Western Sichuan

As one of the rod string of oil and gas wells, tubing string is an important channel to transport oil and gas to the ground, it is also a string that has longer service time in the underground pipe column. The produce can be carried out smoothly depend on whether the tubing string is safe to work or not. The columns are complex in West Sichuan area of underground pipe, pipe string damage seriously, performance of insufficient strength, short service time of tubing. In recent years, the incident of stopping production often occur by the failure of tubing string, to bring a lot of trouble to the production. The tubing string not only has some characteristics of general oil and gas well rod string, but also has its own mechanical behavior characteristics. This paper aimed at the existing problems in Western Sichuan oil column, on the basis of previous research carried out research on the mechanical behavior of column and optimization design, the main ideas includes:(1) To collect the relevant literatures about the mechanics research and optimization design of pipe column at home and abroad, to study the mechanics analysis method of the tubing string and the optimization design method, and put forward to a plan to solve the mechanical analysis and optimization design of tubing string in the West Sichuan area.(2) Based on the analysis of the trajectory of complex borehole in the West Sichuan area, the three spline function of the well depth and azimuth angle is established, and the actual trajectory of the pipe string at any point is solved, the formula of guiding value of three unit vectors in the Frenet standard frame of underground coordinate is adopted. Based on classical model of pipe string mechanics established by Lubinski、Hammerlindl etc, to establish the 3D string mechanical model that include factors of tubing string infinitesimal section in weight, internal and external pressure, sticky lag friction, oil friction, hole bending and packer etc, analysis of the influence on the underground pipe column by piston effect, spiral bending effect, bulging effect and temperature effect, calculate the stress and deformation of the pipe string under different working conditions, according to the boundary condition and the deformation of the pipe string, the force of the pipe string is solved by Newton iteration method;(3) The calculation method of bottom hole static pressure and bottom hole flowing pressure of gas well is studied. Analysis all kinds of gas well productivity equation, according to the productivity equation, the diameter range of the optimal single day output under the certain bottom hole flowing pressure and the well head pressure is determined. The reasonable diameter of the pipe string can be obtained by the friction loss of the pipe string and the critical liquid carrying flow rate.(4) For the choice of the tube column, obtain the hole trajectory by the calculation, establish a three-dimensional model of pipe string and solve its stress, according to the strength theory of material, the strength check method for tubing string is analyzed and selected. Safety and economy of pipe string are analyzed by using safety factor method, for the high safety coefficient of the tube column can be appropriate to reduce the pipe column specifications, for the safety coefficient of the lower tube column can be appropriately increased the tube column specifications, that is, to achieve the optimal design of the tube column.In a well Western Sichuan area Qiongxi as an example, calculation and analysis, the rationality of the established mechanical model and the optimized design project is verified.