Study On Nonlinear Dynamics Action Of Integrated Bit-Rock-Drillstring-Well System

In the process of modern oil drilling,the roller cone bit and drillstring are main drilling tools. Also the performance of the roller cone bits and drillstring directly effect the drilling procees in the form of quality,efficiency and cost.And the effective solution to these problems is to study the dynamic characteristics of the roller cone bit and drillstring system ,which find the kinetic law and mechanical properties of the roller cone bit and drillstring.With the development of modern finite element technology and numerical algorithms,we are able to analyze the dynamic features of the roller cone bit and drillstring .Therefore,the studying of nonlinear dynamic analysis of bit-rock-drillstring-well system is important both theoretically and academically.The structure of roller cone bit and the properties of rock is discussed and based on studies in geometry and kinetics in the paper.According to the structure of roller cone bit and string,comprehensive consideration of bondary conditions,role of various loads and multi-border contact determine conditions,dillstring system was divided into two substructures which are bit-rock and string-well with fixed-interface methods of substructure. Based on dynamic substructure method,random vibration theory,dynamic gap element theory and coupling nonlinear numerical theory, the nonlinear dynamics model of bit-rock-drillstring-well system is established.And the actual working conditions underground of the cone bit and drillstring system reflected under actual state.With the study on decoupling algorithm of nonlinear dynamics model of bit-rock-drillstring-well system, through FEM program, ABAQUS/EXPLICIT central difference, the dynamic simulation analysis is ran about the roller cone bit and string system in the actual drilling engineering. From the simulation result, it can be see that the movement state and dynamic respond distribution of the roller cone bit and string system present complex and irregulation laws. BHA bend and buckle under outer load of WOB,self gravity and dynamic loads which contact the well wall and the bottom. The size of contact force and contact position present great random. Elastoplastic deformation of rock bottom occurred until material damage under contacts collision of the roller cone bit. Great vibrate in vertical,lateral and torsional direction, even couple vibration of the roller cone bit and string system occurred with the roller cone bit and rock bottom interaction. The study conclusion provide theory foundation for enhance of drill bit system life and dynamic optimization of trajectory accuracy, then predicting kinetic laws of the roller cone bit drill string and controlling the trajectory of well.