Research On The Mechanism Of Friction Reduction Of The Hydraulic Axial Vibration In Coiled Tubing Drilling

Coiled tubing drilling(CTD)is a new technology with the characteristic of high efficiency,low cost,and reliable security,which has become a hot research topic at home and aboard.It can not only be sued for old well sidetracking in potential development capacity exploitation of oilfield,but also can be adopted for multi-lateral wells drilling and underbalanced drilling in unconventional petroleum resources and geothermal resources,which has displayed vast potentional and broad application prospects.However,as the CT slides forward without rotation in drilling horizontal wells and it is prone to buckling,the length of lateral extension and the efciency of axial load transmission are usually limited by the high friction.Though the axial hydraulic vibratory tool can reduce the friction effectively and has the advantages of strong operability,predictability and no been affected by the debris and cuttings,the current mechanism of friction reduction is still ambiguity.Based on the analysis of vibration generation,propagation and action with the wellbore of the axial hydraulic vibratory tool,this dissertation explored the firction reduction mechanism of axial vibration,proposed a set of models for the vibration generation,propagation and the length prediction of lateral extension.Then through paogramming and solving the equations,the effect of critical parameters of wellbore,CT and vibratory tool on the results of friction reduction was revealed,which would provide theoretical basisi for the structure optimization and application in CTD.Firstly,a transient hydraulic model with considering the unsteady friction was establelished.Combined with the complicated boundary conditions of bit,the positive displacement motor,hydraulic vibratory tool and drilling pump,the model was solved by programming with the algrathm of modified MOC.Then a series of laboratory experiments was conducted to validate the accuracy and reliability of the model.Through the study of the axial vibration characteristics and the effect of the crucial paramers,such as flow rate,frequency and minimum flow area ratio etc.,on axial vibration,the results indicated that the magnitude of the force induced by hydraulic vibrator is not affected by the frequency of flow area,it increases exponentially with flow rate while decreases exponentially with minimum flow area ratio,the frequency of axial vibration is equal to the frequency of flow area change.Based on the characteristic of horizontal drilling with CT,the effect of axial vibration and pressure fluctuation on the coefficient of firction and normal force was analyzed.The dynamic wave equations were established for mechanical vibration propagation in CT.Combined with the dynamic boundary conditions that the CT drilled continuously,the equations were solved by programming.The axial force reduction at the vertical end of the wellbore was adopted as the performance evaluation standard of the tool.Compared with the axial force with and without the vibratory tool,the mechanism of friction reduction and the effect of critical parameters on the friction reduction performance were studied.The results indicated that the friction reduction was mainly affected by the frequency,amplitude,installation position and coefcient of friction(Co F),whereas the CT size,rate of penetration(ROP)and wellbore curvature affected the tool performance slightly.Based on the study,it revealed the action mechanism of the tool in CTD that the force reduction mainly caused by the direct traction of the tool,the corresponding friction reduction at the curved and buckling section and the change of the bit movement charactersitic.At last,combined with the proposed models and the theory of CT buckling,the prediction method of the lateral extension capability in CTD was derived and validated through the field data.