Improving the rate of penetration in deep well is long-term problems for drilling industry. Pulsed jet drilling which has been proved in field, is a cost-effective way to improve the rate of penetration. An Adjustable frequency pulsed jet generating tool was developed in this paper. The main parts of the adjustable frequency pulsed jet generating tool include turbine, valves, and a resonance pulse chamber. Rotary valve is driven by the turbine. Rotation of the rotary valve causes the state of drilling fluid flow from the continuous to the periodic. So, the periodic flow has frequency and amplitude. In order to obtain higher amplitude, a resonance pulse chamber was used to amplify the amplitude of the periodic drilling fluid flow. The pulsed jet is formed when the periodic drilling fluid flow is issued from the nozzles of the bits. The frequency of the pulsed jet can be easily adjusted by changing the parameters of the rotary valves.
In this paper the working principle of the adjustable frequency pulsed jet generating tool was analyzed. Theoretical calculations and experiments were carried out to reveal the characteristic of the pulsed jet. The effect of the flow rates on the frequency and amplitude of the pulsed jet were studied in detailed. The experiment results show that the pulsed jet with lower frequency and higher amplitude can significantly enhance the rate of penetration in deep wells. The adjustable frequency pulsed jet generating tools have been tested in several wells. The field test results show that the rates of penetration were improved by 15-45% and the tool can meet the operation requirements. Adjustable frequency pulsed jet generating tool as an effective approach to improve ROP, has great application potential in deep well drilling.