Extended Reach Well Drill String Vibration Analysis And Fatigue Life Prediction

During the drilling operations, vertical wells are usually having less accidents than direction wells or extended reach wells, so it’s an important goals for us to solve the problem that how to finish a vertical well or a extended well faster and better.This article is mainly researching the moving law of extended reach well undergrand. The extended reach wells include the straight section, long horizontal section and high-angle section, these sections would encounter many problems such as the control of hole deviation angle and the choice of drilling tools. There are several primary methods to research the string vibration of the extended reach well drilling such as energy method, gap element method and vertical and horizontal bending beam method. We analyse the extended reach well mainly with finite element method and divide the drill string into sevral cells, combine each cell unit as matrix(mass matrix and stiffness matrix), Reference in the classical mechanics of drilling string algorithm and get the spectrum equation of the vibration of extended reach well.because it’s complicated to calculate the equation, so we use the ANSYS software to calculate the vibration frenquency.The fatigue life of drill string should be predicted because it would be fatigued after the steadily working undergrand. Considering the effect of stress-intensification factor, stress amplitude and crack geometry on hthe fatigue life, calculate the fatigue life with different model according to whether the drill string have microcrack. If there is no crack, Miner linear cumulative damage theory would be able to calculate the fatigue life of drill string with stress amplitude and S-N curve. If the drill string have microcrack, Paris model and Forman model would be able to calculate the fatigue life, The former is simple to calculate but the latter is more accurate. But considering the time and other factor, Paris model is better than Forman model in site. This article choose Paris model to calculate the fatigue life of drill string conform to the reality. In order to simplify the calculation, the fatigue point, fatigue stress, fatigue life and danger position of drill string is calculated by self-edited soft Vibration analysis of extended reach well.