The Study On Drill String Vibration Of Extended Reach Well

At present, more and more oil and gas fields in the world output growth depends in large displacement and horizontal wells. Compared with vertical wells, extended reach wells with long horizontal section, slope, long naked eye drop inclined segment features. Reach wells are directional wells, an extension of the horizontal well technology.Reach wells, although there are many advantages and market prospects, However, in the operations and production processes, the column to withstand internal pressure, external pressure, bottom hole drilling pressure, weight, viscous liquid in the tube is the borehole wall reaction forces and other external loading of the combined effects of these factors further restrictions and limitations of a large displacement of the promotion of the well technology. Overall, large-displacement drilling and completion key technology include:optimization of well profile and drill string design, to reduce friction and torque casing, the wellbore trajectory measurement and control technology, wellbore stability technology, wash well with solid control technology, casing wear prediction and prevention technology, and the drill string vibration control technology.The focus of this study is to drill string vibration control technology, strive to summarize a large displacement wells drill string vibration law and proposed damping measures.Domestic and foreign scholars in the string of drill string vibration and control research for many years, analysis of the drill string vibration theory is basically mature, classic method of differential equations, longitudinal and transverse continuous beam method and the finite element method,①The classic The differential equation method is appropriate simplification of the bottom hole assembly and its constraints, mechanical analysis, differential equations and boundary conditions, and then resolved, semi-analytical or numerical method to any question. The②vertical and horizontal curved continuous beam method is an exact solution, it is the drill string as interconnected vertical and horizontal bending of the continuous beam, and three moment equation in the application of mechanics of materials to establish a set of nonlinear algebraic equations. It clear physical concept, a simple calculation. This approach will simplify the mechanical model too much, the larger the actual error.③finite element method is a good method of numerical analysis, especially suitable for solving the regional irregular constraints of complex mathematical and mechanical problems can also set the model to analyze the large deformation problem, but in order to improve the accuracy of the calculation, it have to reduce the cell size, making the already large amount of computation to a sharp increase, affecting the calculation speed. Therefore, the boundary conditions combined with finite element method used in dealing with such characteristics, the method can calculate the complexity of the vibration of the drill string.Therefore, the boundary conditions combined with finite element method used in dealing with such characteristics, the method can calculate the complexity of the vibration of the drill string.On the basis of previous work, the working status of the column to reach wells string of mechanical and mathematical models, combined with the finite element method, three-dimensional kinetic theory of modified Ritz vector method and modal superposition method of drill column natural frequencies and mode shapes and dynamic response of the theoretical analysis. Focus on the use of finite element analysis software ANSYS technology and computer VB programming techniques to develop a set of drill string forces and vibration analysis system software. The software combines the two advantages of the rich window of the VB software and ANSYS software, advanced and sophisticated Finite Element Method, friendly and intuitive interface, can be drawn from the natural frequency of the drill string with the lower part of the drill string combination of changes by adjusting the drill string combination the variation of the amplitude of the drill string dynamic forces of law and the drill string displacement excitation of different frequencies, the paper concludes with the corresponding damping program, technical work to provide a basis for large displacement wells of the drill string vibration control.To complete the main findings and conclusions of this article:(1) Calling ANSYS to write software using VB and calculation of the longitudinal vibration displacement well drill string is a practical method;(2) the length of the drill string, with the increase of the length of the drill collar, low-order natural frequency of vertical vibration of the drill string decreased, but high-end natural frequency was increased;(3) When the entire drill string just to install a shock absorber, you can adjust the shock absorber installation location to change the natural frequencies of the drill string, and present this law:the drill string vertical the natural frequencies with the the installation location of the shock absorber from the increase of the distance of the drill increases;(4) If the drill string used in the two shock absorbers, a fixed, you can adjust the installation location of the other root to change the vibration of the drill string.Damping measures are proposed:(1) most likely due to the natural frequency of longitudinal vibration of the drill string distribution is more dense, resonance. Through modal analysis to determine the natural frequencies of drill bits and rotary speed, to avoid the resonance region;(2) in actual operation, when the apparent jump drill may be appropriate to raise and lower the rotary speed (2-3rev/min), the provision of open resonance region can effectively reduce the bottom hole of the axial dynamic force;(3) using a single shock absorber, shock absorber top of the drill can significantly reduce axial dynamic loading. The bottom hole of the axial vibration damper near the drill bit more ease;(4) pairs of shock absorbers, the first root of the shock absorber close to the drill bit when the second root of the shock absorber from the drill bit farther combinations can reduce the entire drill string axial dynamic load is a better reduction shock program.This article needs to be improved, first of all, this paper is to establish the mechanical model is imperfect, the model to do too many assumptions, such as:column coincide with the borehole axis, borehole omitted for two-dimensional and the drill string lateral and torsional vibration, etc., which are not consistent with the actual situation. Second, the analysis software interactive interface developed in this thesis is too monotonous, and drilling tools database software, which is drilling for optimal combination of inconvenience.