Research On Vibration Mechanics Of Sucker Rod String And System Optimization In Directional Wells

During the working process of pumping wells,there is obvious vibration of sucker rod string(SRS).The vibration of will affect dynamometer cards and rod-tube contact state,then affect the energy consumption and the rod-tube eccentric wear of oil wells.Therefore,the research on SRS vibration is the optimization basis of oil well energy-saving and rod-tube eccentric wear prevention.At present,the research on SRS vibration mechanics is still defective: The influence of gas-liquid separation in the pump(GLSIP)is not considered in SRS longitudinal vibration model;The curved wellbore excitation is not considered in the vibration model of SRS with axial reciprocating motion;The excitation of SRS torsional vibration is not proposed.As for the above defects,and using static and dynamic curve coordinates to describe the axial relative position between SRS and tubing,then the mechanical and mathematical models for the simulation of SRS vibration are established.The numerical simulation models are established by the combination of spatial discretization,time continuity and numerical integration.Based on the simulation of SRS vibration,the optimization design methods of energy saving and eccentric wear prevention are studied.Finally,the accuracy and practical engineering significance of the models are verified through the field test data.Considering the influence of GLSIP and liquid hammer force,the bottom boundary condition of SRS longitudinal vibration is established based on continuous flow equation and momentum conservation;At the same time,considering the influence of axial reciprocating motion of SRS on rod-tube Coulomb friction,the coupling simulation model of longitudinal vibration of SRS and fluid pressure in pump is established.Simulation results show that: the dynamometer cards are significantly affected by GLSIP.The effective downward resistance of SRS is obviously increased by liquid hammer force.On the basis of considering the SRS initial bending,tubing constraint,alternating axial load excitation and rod-tube collision excitation,the excitation of curved wellbore to SRS transverse vibration with axial reciprocating motion is proposed,then the simulation model of SRS transverse vibration is established.Simulation results show that the rod-tube contact state and contact force will be significantly affected by curved wellbore excitation.Based on the current longitudinal transverse and torsional coupling vibration model of SRS,considering the mutual coupling of longitudinal transverse and torsional motion parameters caused by SRS axial reciprocating motion in curved tubing,and considering the excitation of friction torque generated by longitudinal and transverse coupling vibration to SRS torsional vibration,then the simulation model of SRS longitudinal transverse and torsional coupling vibration is established.Simulation results show that: longitudinal vibration is less affected by transverse and torsional vibration.Transverse vibration is obviously affected by longitudinal vibration.There is obvious torsional vibration of SRS under the excitation of friction torque.Considering the GLSIP,the discharge coefficient simulation model of oil pump is improved.Considering the dissolution,precipitation,compression and expansion of gas in the annulus between tubing and casing,the simulation model of dynamic liquid level in intermittent pumping process is established.According to the characteristics of tension bending and torsion multiaxial stress of SRS,the strength design criterion of SRS in directional wells is established.Based on above researches,the optimization design methods of energy-saving and eccentric wear prevention are established.Simulation results show that: the oil well dynamic parameters are obviously affected by the GLSIP.The dangerous point of fatigue failure may appear in the compression section of SRS.The energy-saving optimization design method can greatly reduce the energy consumption of oil wells.The optimization method of centralizer layout can prevent the rod-tube eccentric wear.The accuracy of the simulation models of SRS vibration and system dynamic parameters is verified based on the field measured data(suspension dynamometer card,electrical parameters and production)and the operation records of oil wells.The significance of optimization design methods of energy-saving and eccentric wear prevention is verified by comparing the operation state of oil wells before and after optimization.