Study On Vibration Law And Thread Connection Strength Of Drill String Under The Action Of Hydraulic Oscillator

Extended reach well drilling is a new type of drilling technology developed on the basis of directional well and horizontal well drilling technology,which is mainly developed to meet the needs of offshore oil and land production and one well production of multiple unconnected oil and gas reservoir structures.However,in the process of drilling extended reach wells,with the increase of the length of horizontal section,there will be a large friction between the drill string and the wellbore,and the formation of pressure supporting effect makes it difficult to transfer the WOB to the bit.In order to solve the pressure supporting effect caused by too large friction between the string and the wellbore,a variety of tools for reducing friction and drag have been developed,among which the hydraulic oscillator tool has a good application prospect.However,the following problems will be encountered during the operation of the hydraulic oscillator: 1.The influence of the performance parameters of the hydraulic oscillator on the vibration of the drill string;2.Whether the fatigue damage is caused to the connecting thread of the hydraulic oscillator during the operation.According to these two problems,this paper carries out in-depth study.Based on the working principle of mm hydraulic oscillator,this paper explores the friction change between the drill string and the borehole wall when it vibrates.By comparing the three friction models,the Coulomb friction model which is easy to obtain parameters is selected as the calculation method of friction in this paper.The theoretical method of the vibration analysis of the whole well drill string is established,which provides theoretical guidance for the establishment of the finite element model of the whole well drill string vibration with friction.According to the actual BHA of horizontal well,the friction element is added to the model by ANSYS APDL.Static analysis and modal analysis are carried out on the model respectively to obtain the static axial force and the natural frequency of the drill string on each thread of the drill string system,and the transient dynamic analysis is carried out on the model.The working parameters of the hydraulic oscillator are set: amplitude of the exciting force,vibration frequency,working position and well inclination.The amplitude of the drill string is taken as the evaluation standard to obtain the amplitude of each parameter Among them,the larger the amplitude and frequency of the excitation force are,the farther the effective working range of the hydraulic oscillator is,and the distance is within 1300 m.By setting up the orthogonal experiment and using the orthogonal data analysis method to sort out the results,the influence degree of each parameter on the transmissiondistance of the excitation force is obtained as follows: installation position > excitation force amplitude > vibration frequency > well angle.In order not to lose the effective working range of the hydraulic oscillator,the installation position should be more than650 m from the bottom of the drill string.In this paper,the finite element models of three common types of screw thread are established for analysis,and the reasonable boundary conditions are defined.The sum of the static axial force on the connecting thread of the hydraulic oscillator and the maximum exciting force that the hydraulic oscillator can produce is applied to the upper end of the screw thread as the external load,and the data results(equivalent stress value of each tooth root,axial stress value,stress value at the arc of the shoulder surface)are obtained The load distribution of thread and the stress value of dangerous point are obtained.The exciting force produced by the hydraulic oscillator is gradually increased and applied to the upper end of the thread model.Through the stress value of the thread dangerous point obtained and the fatigue strength calculation,when the safety factor is lower than the allowable safety factor,it is considered that the vibration produced by the hydraulic oscillator causes fatigue damage to the thread.It is found that the exciting force produced by the hydraulic oscillator will not cause the thread to be made in the range of 50kn-80 kn Fatigue failure.The research results of this paper can provide theoretical guidance for determining the working parameters of the hydraulic oscillator in the process of horizontal well drilling.