Research On The Evaluation Method Of The Axial Vibration Drag Reduction Effect Of Three-dimensional Horizontal Wells

In recent years,our country continues to push the exploration and development of unconventional resources and promote the concept of cost reducing and benefit increasing.The complex structural well,such as horizontal well and cluster well,has increasingly become an indispensable technological means for developing the reservoirs efficiently.However,the complicated well trajectory derived a lot of downhole complications,such as high drag and torque and serious backing pressure.All of these problems have brought severe challenges for the design and operation of horizontal wells.As a representative of drag reducer,the friction reduction effect of hydraulic oscillator has been widely recognized by drilling engineering,but the researches on evaluating the effect of friction reduction induced by hydraulic oscillator are relatively lagging.Therefore,this paper,which is based on the theories of drill-string mechanic and tribological principle,and adopted a method that combines theory study,simulation analysis and experimental research,carried out the research of friction reduction characteristic of hydraulic oscillator and its evaluation methodology in the course of drilling horizontal wells.The primarily work and achievements of the paper are as follows:(1)The experimental apparatus on simulating the friction reduction induced by axial vibration was developed.By using the experimental apparatus,three kinds of experiment has been carried out,which including sliding friction test,verified experiment of friction reduction induced by axial vibration and friction test coupling with sliding and axial vibration.The experiment results of sliding friction show that the lubrication effect of fluid in an order from strong to weak are oil based mud,water based mud and dry friction,and the corresponding average friction coefficient is 0.41,0.36 and 0.27,respectively.The results of verified experiment prove that the prerequisites for reducing friction caused by axial oscillation tools are that the relative sliding velocity of the drill-string on the borehole rock should be less than the amplitude of the velocity of the axial oscillation tool vibration.The friction coupling test results indicate the friction force takes on a periodic gradual process when combing axial vibration with sliding,and then makes the total friction force in one period decline.(2)As the classical Coulomb model has problems with adaptability and accuracy,this paper conducted a targeted research on friction coupling model.By contrasting and analyzing the advantages and disadvantages of different dynamic friction models,the Dahl model was selected to describe the sliding friction phenomenon coupling with axial vibration.Computational models were developed and implemented in a combined Matlab-Simulink environment.The results indicate that calculations of Dahl model are found to be in agreement with the experimental results,and which is obviously better than the Coulomb model.The correctness of the model and method in this paper are verified.And on this basis the dynamic parameter of Dahl model has been identified by using experimental method.As for the sliding friction between shale rock and metal,the determined value of kt ranges from 35?40 N/mm.(3)A new mechanical evaluation method of friction reduction by axial vibration for horizontal well was proposed.Considering the deformation of drill-string under the effect of axial vibration,the vibration characteristics of hydraulic oscillator has been studied.The research shows that the axial vibration induced by hydraulic oscillator will not bring impact to MWD tools and drill bit.Considering the influence of dynamic friction and viscous forces,a model was established to analyze the operating scope of axial vibration quantitatively.Given this understanding,a new model,which combines the conventional drag and torque model with dynamic friction model,was established to analyze and forecast the frictional resistance in horizontal drilling under the action of hydraulic oscillator,and gave the corresponding algorithm procedures.This model can exactly predict the drag and torque during drilling horizontal wells using hydraulic oscillator.It offered a simple and effective method for evaluating the effect of friction reduction caused by hydraulic oscillator.(4)The rationality and the veracity of the mechanical evaluation method of vibrating drag reduction have been verified by the application of field case study.Based on the hydraulic oscillator's field application data in well W204H10-1,the application evaluation of hydraulic oscillator has been discussed,and the reasonable assembling site was optimized and studied.The analysis shows that the drag of sliding drilling was decreased from original 261.33kN to 231.33kN,the corresponding friction reduction rate is 11.48%.The optimized result of drag reducer's proper location indicated that the relative distance between hydraulic oscillator and drill bit should be greater than half of its' operating scopes,while it should be located as close as possible to the bit,and the relative distance.