Design and hydraulic modeling of pulse grinding bits for horizontal wells

If cuttings carrying performance is poor and cuttings removal is not in time during the drilling of horizontal wells, drilling cuttings will accumulate in the lower sections, leading to backing pressure, BHA binding and even drill pipe sticking. In this paper, a new type of Helmholtz pulse grinding bits suitable for horizontal wells was designed based on the theory of Helmholtz oscillation chamber to generate pulse, jet pump and high pressure jet after the formation of cuttings beds was analyzed. In this type of bit, a high-speed pulse jet is used to assist rock breaking, a reverse jet is used to remove the cuttings at the bottom of the bit under negative pressure, and its inner grinding structure is used to reduce the particle size of cuttings. By using this bit, efficient cuttings removal and rock breaking will be both realized, the chip hold-down effect will be reduced and the cuttings beds in a horizontal well will be also removed. Then, the hydraulic models were established for a pulse generation device, an efficient rock breaking device and a reverse swabbing device, respectively. It is shown from the simulation results that the optimal resonance flowrate increases with the increase of the diameters of an inlet chamber and a feedback chamber and with the decrease of the diameter of a resonance chamber, and it is approximately in linear relationship with each factor. The optimal flowrate ratio of the reverse swabbing device increases first and then decreases with the increase of dimensionless flowrate ratio, and decreases with the increase of dimensionless area ratio. It is indicated from example analysis that the inherent frequency of Helmholtz oscillation chamber is 24.00 Hz, the optimal oscillation flowrate is 23.92 L/s and the optimal flowrate ratio is 0.59. Based on case studies, the accuracy of hydraulic models is verified. It is concluded that this new type of bits provides a new solution to the accumulation of cuttings beds.