| With the development of the world economy,the demand for oil and natural gas is increasing in the worldwide,which results in the increasing intensification of the exploration and development of oil and gas resources.And with the increase of the exploitation degree,the exploration and development of oil and gas resources have gradually progressed toward deeper oil and gas,which has led to the increase of the number of complex structural wells such as deep wells,ultra-deep wells,horizontal wells,high-angle wells,and large-reach wells.However,the drilling friction is significant during the drilling of horizontal wells and extended reach wells,which has become a vital issue in limiting the development of drilling technology for horizontal wells and extended reach wells.Drilling friction resistance has reduced the drilling efficiency and has largely limited the wellbore-extending,and then the exploration and development of oil and gas resources has been affected.Therefore,in order to reduce the drilling friction and improve the drilling efficiency,the technology of reducing friction has become the research focus of the horizontal wells and extended reach wells technology.Aiming at reducing the drilling friction,a Jet-type anti-friction tool has been proposed in this paper,and the following research has been carried out which include numerical simulation,experimental verification and friction reduction characteristics.Firstly,with the combination of application background,the structural design of the Jet-type anti-friction tool has been completed,which is consisted by absorber and jet oscillator.The torque is transmitted downwards through the thread pair and the roller to drive the bit rotate.The weight on bit(WOB)is from the weight of the upper column,which act on the mandrel through the disc spring and the damper shaft.And then WOB is transmitted to the drill bit.A pressure drop change is generated through the action of the jet joint and the jet oscillator generates a jet oscillation to form an axial impact.On the basis of structure design,the performance analysis of the shock absorber is researched further to establish the calculation model of the load-displacement characteristics,the stiffness characteristics and the stress characteristic.Under the loads,the load-displacement curve is linear and the stiffness-displacement curve is nonlinear.FLUENT software conducts the CFD numerical simulation study of the Jet-type anti-friction tool,and the numerical simulation of the fluid in the jet joint is completed.The wall-to-wall switching process exists in the jet joint and the velocity flow line and the pressure distribution of the center section of the fluid are obtained,as well as the pressure changes at the split-flow center point.As the increase of the inlet flow,the outlet flow rate gradually is increasing and the increased speed is faster than the inlet flow rate.The inlet pressure and the outlet pressure also gradually increase,but the inlet pressure increase speed is higher than the outlet pressure.The pressure fluctuation presents irregular change at the initial stage and the pressure appears periodic fluctuations when the jet keeps stable at the split-flow center point.The randomness of wellbore friction and its influences on the drill string dynamics are studied by establishing the dynamic model of the drill string under horizontal well conditions.Based on this,the study of vibration-reducing friction characteristics is carried out.Firstly,the force analysis of the drill string in the horizontal well is conducted and the analysis model of the drill string dynamics is established.Then the friction randomness between the drill-string and the wellbore is researched.The step and method to build the randomness field of wellbore friction are given and the description method of the randomness behavior of wellbore friction is obtained.The solutions of each force are given in the model.Considering the contact conditions of different points located in the drill pipe,the discretization method of the dynamics model is achieved to solve the dynamics model.And the vibration displacement,vibration speed,and drilling efficiency are obtained.Through indoor bench test,the work pressure drop,vibration frequency and vibration displacement of the Jet-type anti-friction tool are tested.And the test results are compared with the theoretical calculation results.The test pressure drop test results and the numerical simulation results of the tool present same distribution law,vibration frequency and vibration displacement test results can achieve expected results.In summary,with the combination of the structural feature and working principle of the Jet-type anti-friction tool,the numerical simulation research is conducted,and the bench test verifies the accuracy of numerical simulation.For the application in the horizontal well conditions,the vibration-reducing friction characteristics are analyzed,which can provide a preference for the drill string dynamics that is based on the randomness of wellbore friction and the vibration reduction research of the drill string in the downhole. |
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