Study On Mechanics Of Rod String In Surface Driven Screw Pump

The surface driven screw pump oil production system is widely used because of its high oil production efficiency and small land occupation.When the system works normally,the rod string transmits the driving torque from the ground to the screw pump rotor,which makes the screw pump work and lift the oil to the ground.Because the well depth is generally 1000 meters,and the diameter of the production string is tens of millimeters,the production string is a typical slender rod,so the downhole production string is easy to deform and even collide with the tubing under the action of external force in the working process,which leads to the failure of the string or tubing and affects the normal work of the string,and the failure of the string is mainly caused by the lateral vibration of the string.Therefore,in this paper,in addition to the analysis of the external force on the rod,the mechanism of the transverse vibration of the rod is also studied.In view of the above problems,this paper has carried on the following aspects:(1)This paper analyzes the structure and working principle of screw pump,establishes the geometric and mathematical model of screw pump stator and rotor,and studies the motion law of rotor.The friction torque of screw pump rotor was simulated by FLUENT software.The influence of eccentricity and pressure difference on the friction torque was analyzed,and the mechanism of flow force was studied.(2)The geometric model of rod tube annulus flow field is established,and the grid generation and environment setting are carried out.Based on the dynamic grid,the force and flow field characteristics of rod string are simulated.Based on fluent,the effects of crude oil density,rod diameter,crude oil viscosity,eccentricity and rotation speed on the force and characteristics of annular flow field were analyzed,and the mechanism of annular flow field acting on rod was studied.The regression models of friction torque,radial force and tangential force of annular flow field on rod string under various factors are established.(3)It is pointed out that the eccentric rotation at the bottom of the rod string is the excitation of the transverse vibration of the rod string,and the eccentric rotation of the rod string caused by the transverse vibration further stimulates the transverse vibration of the rod string,which reveals the mechanism of the transverse vibration of the rod string in screw pump production.The simulation model of rod string transverse vibration in screw pump production is established,and the simulation of rod string transverse vibration law and rod tube collision contact force is realized.