The friction-reducing principle and application of the drill string with a hydro-oscillator

In order to solve the problem related to effective weight on bit (WOB) transition during shale gas long departure horizontal well drilling, the hydro-oscillator has been applied more and more both in China and abroad to reduce drill string drag and enhance the rate of penetration (ROP) for the horizontal section drilling, which can greatly reduce the cost of shale gas horizontal well drilling. This paper presented a theoretical relation between axial vibration velocity and friction coefficient of drill string, analyzed the principle of reducing friction by the use of the hydro-oscillator. On the basis of principle that axial vibration can reduce drag and taking well bore trajectory, drill string combination, the hydro-oscillator structure, etc. into account, a dynamics analysis model for full-well drill string with the hydro-oscillator was established. The effects of installation location, maximum vibration force and vibration frequency of the hydro-oscillator on drag reduction were simulated, and comparison and analysis had been carried out by using field data, with the calculation results providing a theoretical basis for the field application of hydro-oscillator and the optimization of structure parameters.