Dynamic Simulation Of Drill String Work Behavior During Horizontal Well Drilling

At present,large displacement wells and horizontal wells have become the main types of oil and gas exploration and development process.However,the extended drilling ability of horizontal wells is seriously restricted due to the dynamic changes of well inclination,long horizontal displacement,large friction torque and difficult control of wellbore trajectory.Clearing the dynamic working behavior of the drill string in the drilling process and exploring the method to reduce the friction torque of the drill string have become the key to avoid premature failure of the drill string,evaluating the dynamic working safety of the drill string and improving the development level of horizontal wells.In this paper,the dynamic characteristics of drill string and the change rule of friction torque are studied by combining simulation and experiment.The main contents are :(1)Based on the finite element method,the dynamic equation of drilling string in horizontal well is studied and established,the contact state between drilling string and wellbore is discussed,and the boundary conditions for solving the dynamic equation are determined.(2)Based on ADAMS software,the simulation model of the whole wellbore and drill string system of horizontal wells is established,and the reliability and correctness of the model are verified.(3)The lateral vibration,torsional vibration,trajectory,motion state,contact state with wellbore and friction along the wellbore of the drill string system are studied.The results show that the lateral vibration intensity of the drill string in the lower part of the bending section and the front part of the horizontal section is high.The torsional vibration at the bit is most obvious;The overall trend of drill string is inclined to the lower wall,showing a rolling motion state in the random motion process;The contact state between drill string and borehole wall in bending section is complex,and the horizontal section is relatively stable;Rotary drilling can reduce friction by about 15 % compared with sliding drilling.(4)The influence of drilling pressure and rotational speed on the contact of drill string under simulation and real test conditions is studied and compared.The influence of drilling pressure and lateral force on the instability and deformation of drill string is analyzed.The friction and torque variation of rotary drilling of horizontal well drill string are studied.The results show that the simulation model has certain accuracy;Drilling pressure intensifies the instability deformation of drill string,and lateral force changes the bending direction of drill string after instability deformation.The wellhead torque and hook load showed a fluctuating trend.