Nonlineaer Study On Dynamic Action Of Integrated Drill String-Well Rock System

It is the key technical issue in the drilling engineering that effectively predicting and controlling of dynamic performance and kinetics law, reasonably increasing the strength of drill bit and drill string, realizing the control of trajectory precession. And the solution to these problems is one of basic work to establish rational and reliable dynamic model for drill bit and drill string, which find the kinetic law and mechanical properties of drill string under well. However, the large and complex structure of drill string, the study is very hard by physical experiment, the drill string, in the drilling process, exist not only vertical vibration, lateral vibration and torsional vibration, but also the coupling of three direction vibration, the general stress analysis method is difficult to solve. Therefore, the studying of dynamic properties of drill string system under drill string structure and wall rock interaction is an theoretical and practical value to realize of predicting of kinetic law and controlling of trajectory precession.Paper combine the random vibration theory,finite element method,dynamic gap element theory,coupling nonlinear numerical theory and modern drilling technologies. According to the drill string kinetic and force state, comprehensive consideration of drill string structure,boundary conditions and role of various loads, introduction of dynamic gap element, the nonlinear dynamic model of drill string system is established, which couple vertical vibration,lateral vibration and torsional vibration, and which is not only a nonlinear geometry and damping problem but also nonlinear boundary condition problem. The dynamic properties of drill string system is more fully reflected under actual state.Through FEM program, ABAQUS/EXPLICIT central difference, the dynamic simulation analysis is ran about drill string system in the actual drilling engineering, which research kinetic law of drill string in the drilling process,mechanical properties,failure mechanism. From the simulation result, it can be see that the movement state and dynamic respond distribution of drill string system present complex and irregulation laws. BHA bend and buckle under outer load of WOB and self gravity, which contact the well wall, the size of contact force and contact position present great random, the BHA move close to well wall and great vibrate in vertical,lateral and torsional direction, even couple vibration. The transverse direction trajectory curve of various node on drill string axial direction exhibit random. The study conclusion provide theory foundation for enhance of drill bit system life and dynamic optimization of trajectory accuracy, then predicting kinetic laws of drill string and controlling the trajectory of well.