Development of small diameter hydraulic agitator with cable for directional drilling in underground coal mine

Aiming at the problems of large drilling pressure, low drilling efficiency and limited hole depth caused by the backing effect of drill string during deep hole directional drilling in underground coal mine, the technical idea of using hydraulic agitator was proposed. The ø89 mm small diameter hydriculic agitator was designed based on valve principle, the exciting force, excitation frequency were identified, and the cabled sub was developed. The performance parameters of hydraulic agitator with disc spring and cylindrical spring were tested. The results show that when the flow rate of 300 L/min the disc spring hydraulic agitator has the maximum pressure drop of 1.9 MPa, the exciting force of 8.11 kN, the frequency of 13 Hz, can be installed near the bit for friction reduction partly. The maximum deformation of drill string is 2.86 mm, the reset force is 7.98 kN, the frequency is 11 Hz with cylindrical spring with 150 m cabled drill string under the flow rate of 300 L/min. The agitator was used when the baking pressure was obviously generated during drilling No.10 hole in -600 m drainage lane, in Zhangji coal mine of Huainan. The average drilling pressure was reduced by 33% and the average drilling efficiency was increased by 126%. The friction of drilling was significantly reduced and the efficiency of directional drilling was improved. The developed small-diameter ø89 mm cabled hydraulic agitator provides a solution for the backing pressure problem in horizontal directional drilling in coal mines.