Research On Drill String Dynamics Of Active Axial Vibration Reducing Drill String Friction In Shale Gas Horizontal Well

In recent years,the demand of natural gas increased dramatically with the high speed development of nation’s economy in China,which poses new challenges to the safety of energy supply.Since the shale oil and gas resources were exploited successfully in North America,China also took some effective measures to accelerate the exploration process of shale gas.In order to improve the individual well producing rate,long displacement horizontal wells were widely applied in the construction of shale gas wells.During the drilling process,the high friction which is caused by long displacement well trajectory affects the transport of weight on bit,thus resulting in a low rate of penetration(ROP)in horizontal section.For the sake of reducing well string friction and increasing ROP,the active axial vibration tool has been widely used and generates some favorable benefit.Based on the working principal of active vibration tool,this paper discussed the relation between friction force of wear unit and relative slip rate and analyzed the advantages and disadvantages of different friction models.It established a friction model for axial vibration tool,and optimized the correlation parameters according to the experimental data.With this model,it studied the relation between friction factor and axial slip rate under the effect of axial vibration of drill string.Considering the influence of well trajectory,drill string structure,well structure,the contact between drill string and side wall,drilling fluid,weight on bit and working parameters of axial vibration tool,a finite element model of drill string with active reducing friction tool for shale gas horizontal well was developed to conduct mechanics analysis about drill string.Besides,an evaluation model for the contact between drill string and side wall was also developed according to the theory of interstice unit.The contact drill string were confined when the contact occurred between drill string and side wall and generated a relative motion.During the simulation of vibration behavior of drill string in the full wellbore,the central difference method was applied to analysis the effect of vibration frequency,maximum vibration force and installation position of axial vibration tool to the drill string friction.The study results demonstrated that the vibration frequency and maximum vibration force of active reducing friction tool have a large influence on the reducing friction effect.The drill string friction decreased with the increase of vibration frequency of the tool and then had an increase trend.Actually,the tool gets the best reducing friction effect when the frequency is 16 HZ or when the vibration force is 39 kN.The farther the distance of drill string from the tool,the smaller the axial speed is.Specifically,the effect of reducing friction is weak when the distance is about 400m,while the effect is better when the installation position is 220-320m from bit.According to the field data of C1 shale gas well in Weiyuan-Changning district,it calculated the hook load of C1 well with the presented model.The range of relative error between the calculated results and the measured results is 5.74%-8.31%,which demonstrated the reliability of the presented model in this paper.This research provided the theory support for the field application of active axial reducing friction tool in the shale gas horizontal well.It has an important theoretical significance and a promising application perspective.