Study On Fatigue Life Of Drill Pipe For Oil And Gas Wells

The drill pipe is the most prone to failure and damage in oil and gas well drilling,so the fatigue life of the drill pipe and the strength of the drilling rig restrict the drilling process and construction process.Drill in poor working conditions and complicated force conditions by wear,corrosion and non normal damage will accelerate the drill pipe rupture,leakage failure,drill the working conditions of complex geological conditions and other factors affect the fatigue life of the drill pipe is difficult to predict,the fatigue life in design of drilling technology and construction in the process it is difficult to effectively control the drill pipe,so it is necessary to drill working conditions,the stress of model,using the fatigue life calculation model and obtain the drill pipe reasonable fatigue life obtained,to guide the overall design of drill pipe and reasonable design and construction process.In this paper,through the analysis of the drill pipe condition,establishing mechanical model of drill pipe in construction conditions,obtain the constraint model of the drill pipe in the working state of the Shii Kong and drill,through the research on the method of analytical method and the finite element analysis and experiment on fatigue life of drill pipe.In this paper,the stress state of motion,the drill pipe drilling process research model,geometric equation,the establishment of drilling force model based on the equilibrium equation,the force model of drill pipe drill pipe in borehole is derived under the restricted condition of bending stress calculation formula,and get the hole on the drill pipe constraint state.The fatigue life of Paris and Forman drill model prediction method was studied and predicted by formula derivation based on the fatigue life of drill pipe of oil and gas well;the fatigue life calculation formula based on the fatigue life of drill pipe is on the fatigue life of a drill in the initial crack,and puts forward the methods to improve the fatigue life of drill pipe.This paper,by using 3d software modeling to simulation model,the static analysis using finite element software for oil and gas Wells with drill pipe,and the analysis of the fatigue life of the threaded portion were studied with finite element analysis,the main stress and fatigue life,through the analysis of the maximum stress and minimum fatigue life of the drill pipe at the roots of male thread.According to theoretical analysis and simulation research,the minimum fatigue life of the drill pipe body is 5.25×10~6 when the maximum cracks under 1mm are generated under transportation and other collision conditions,and the fatigue life of the screw thread is 5.1×10~5 when cracks are not considered.The fatigue life of the drill pipe body is 10 times that of the screw thread when there are common cracks.Based on the drillpipe fatigue life experiment system and the studied drillpipe constraint model,the fatigue life of the drill pipe simulated in the laboratory is obtained,and the fatigue life obtained by analytical method and simulation method is compared.Theoretical analysis and experiment prove that the minimum fatigue life of the drill pipe studied occurs at the root of the common thread.