| High abrasiveness,hardness and compactness is the properties of deep formation,which is the main causes of the low ROP in deep wells.It is believed that the rotary percussive drilling is one of the most efficient methods to promote the ROP in hard rock,the basic principle of rotary percussive drilling is to take the advantage of the down hole drilling fluid energy,and transfer the hydraulic energy to impact energy through the device.However,the hydraulic energy loss increases with the increasing of the well depth,which would influence the application of the impact in deep wells.Therefore,more other external energy need to be taken into consideration to modulate the impact load,in order to broaden the application range of the impact drilling tools.Two different impact modulation methods are put forward in this paper,one is drill string vibration assisted percussive drilling,and the other is impeller percussive drilling device.The main contents contains:（1）Therefore,based on the stress wave theory,the differential equation of impact load and displacement under different incident stress waves（exponent,rectangle,triangle and sine forms）is established,and the energy transfer efficiency is calculated under the four shapes of stress waves;（2）according to the theory analysis,a drill string vibration assisted percussive drilling device is put forward;as well as an impeller percussive drilling device.Fluid-structure interaction is used to analyze the output impact of the device for the former device;and for the impeller percussive drilling device,based on the impeller rotating law,the output load form and influence factors are analyzed.（3）Lastly,the rock-bit rock breaking model is established based on the D-P criterion,the law of the rock breaking under four impact forms（exponent,rectangle,triangle and sine forms）is explored in shallow and deep wells respectively;then the rock breaking performance of two devices were compared.Theoretical analysis,numerical simulation and experimental methods are applied in this paper.（1）It is indicated that the energy transfer efficiency of rectangle and sine stress wave is81%and 80%,respectively,and to the exponent and triangle wave,the energy transfer efficiency is 54%and 48%,which shows that the waveform of the incident stress wave is the main factor to influence the rock breaking efficiency;besides,through the analysis of the optimal stress wave form characteristics,it is represented that sine wave form impact should be the goal to modulate,providing the fundamental theory for the impact modulation device design.（2）Through the simulation of the two devices,it is indicated that the output load is closed the sinewave shape,and at the same working conditions(flow rate is 30 L·s-1),the output load are70 k N and 67 k N and the variation frequency are 6 Hz and 26 Hz,respectively.The output load of the former device is influenced by the the WOB,amplitude of WOB and outlet size.The vibration frequency is affected by the frequency of WOB and spring stiffness;the output load of the latter device is affected by the structural parameters and working parameters,which including width installation position,vane number,structures of impeller,inlet flow rate and outlet size.Through the comparison of the two devices,the performance of the vibration assisted drilling device is affected by the variation of drill string vibration significantely,whereas the impeller percussive drilling d evice consuming the hydraulic energy,but could generate a steady impact load.（3）Under the different impact waveform loads,the hard rock in deep wells drilling performace under impact load was much better than that of soft rock in shallow wells,meanwhile,the drilling performance is different under different waveform loads,at the same time,under the combination of lower static plus high impact amplitude,an optimal impact frequency is existed,which could have the best rock breaking performance. |
PDF Full Text Request