Abstract
Activating drill string vibration is an effective means to mitigate the excessive drag encountered during drilling complex-structure wells. However, the Coulomb model cannot describe the sliding friction behavior between drill string and borehole rock with imposed axial vibrations. To solve this problem, a specially designed experimental setup was utilized to investigate the characteristics of axial vibrating-sliding coupling friction. The results indicate that when vibration velocity is greater than sliding velocity, axial vibration can significantly reduce friction force between contact surfaces. Its friction reduction mechanism embodies not only the changes of instantaneous friction force, but also friction coefficient. Meanwhile, a friction coupling model was established based on the Hertz contact theory and Dahl model. The corresponding computational program was developed in Matlab/Simulink environment. The calculation results are in good agreement with the experimental results, verifying the validity of the present method. Furthermore, to overcome the shortcoming of Dahl model, a dynamic friction coefficient model was proposed to evaluate the friction-reducing effect of axial vibration using dimensional analysis method. The model parameters under different lubrication conditions were retrieved through inverse calculation with experimental data. This method provides a new solution for evaluating the friction-reducing effect of hydraulic oscillator and optimizing its placement.
Highlights
The frictional contact problem between drill string and borehole rock is a basic research topic in drilling engineering [1,2,3]
Excessive drag encountered in complex-structure wells with the sliding drilling mode severely restricts the improvement of rate of penetration (ROP) and ultimate extension distance [4, 5]
The Empirical Mode Decomposition (EMD) [27] has been adopted in this paper to decompose the experimental data into number of Intrinsic
Summary
The frictional contact problem between drill string and borehole rock is a basic research topic in drilling engineering [1,2,3]. Excessive drag encountered in complex-structure wells (such as horizontal wells, extended-reach wells, and multilateral wells) with the sliding drilling mode severely restricts the improvement of rate of penetration (ROP) and ultimate extension distance [4, 5]. According to the statistics from Roberto et al [6], approximately 30% of the total drilling time was spent to adjust wellbore trajectory and control azimuth with slide drilling mode during drilling directional or horizontal wells, and the produced excessive drag made it progressively more difficult for the drill string to slide smoothly. The overall gross ROP is much less during sliding mode with a steerable motor than during rotating mode. How to reduce the excessive drag caused by drilling complex-structure wells with sliding mode has become a key issue needing urgent solution in complex oil and gas development [7, 8]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
