CAVIJET™ Augmented Deep-Hole Drilling Bits

Abstract

Drilling bits which exploit the destructive energy of cavitation are being developed. A systematic series of tests is now under way, first to establish feasibility, and then to define the effective adaptation of the CAVIJET™ cavitating water jet method for augmenting the cutting action of mechanical deep-hole drilling bits. Successful drilling tests, using a 1/4-in. (6.4-mm) CAVIJET nozzle, were performed at atmospheric pressure and in a test chamber which provided simulated wellbore pressures up to 3000 psi(21 MPa). The effect of back pressure on standoff distance, and a comparison of steady jet versus CAVIJET cutting efficiencies are discussed.

The Effects of the Downstream Contraction Ratio of Organ-Pipe Nozzle on the Pressure Oscillations of Self-Resonating Waterjets

“…So, this nozzle was used in this study, aiming at enhancing the rate of penetration of roller bits in deep-hole drilling. The working principles and geometry of organ-pipe nozzles are briefly shown below, and more detailed information can be found in the work done by Conn et al [13][14][15][16][17].…”

“…where S t is the critical Strouhal number, with a general value of 0.3 used in SRWJ [13][14][15][16][17]35]; U e is the jet velocity, m/s; and c is the local sound speed, m/s. The peak resonance not only transfers the continuous jet into a pulsed one but also dramatically accelerates the cavitation in the flow by changing the jet structure into discrete ring vortex, which enables the jet to have a strong erosion ability.…”

“…To be more specific, one accumulator was located near the pump and the other one was placed close to the nozzle, shown in the figure. A static pressure transducer (Model: DMK 331P) was employed in the experiment, used to monitor the inlet pressure (P i ) In addition, two inlet pressures of 10 MPa and 20 MPa were used in the experiment, which was determined by the pressure of the SRWJ used in practical applications of deep-hole drilling [13,15]. The main parameters of the transducers are shown in Tables 1 and 2, respectively, and FS means full scale.…”

“…This is due to the fact that the ambient pressure controls the cavitation number if the pressure drop across the nozzle has been determined, while the ambient pressure is in turn determined by the drilling depth. In order to solve this problem in deep-hole drilling, Conn and Radtke [13] proposed the concept of self-resonating waterjets (SRWJs), which combines the advantages of both a pulse jet and a cavitating jet. In their experiment, successful drilling tests were performed in a chamber which provided simulated wellbore pressures up to 21 MPa, and the results showed that organ-pipe nozzles produced more effective erosion action in comparison with conventional nozzles under the same operating conditions.…”

“…Despite a great many investigations on SRWJ, it should be noticed that the optimal values of the downstream contraction ratio of organ-pipe nozzles are still unknown and need to be studied. So far, the organ-pipe nozzles used in the research are all manufactured using an equation that only gives the ratio of the chamber length to the exit diameter [13][14][15][16][17][18][19][20][21][22][25][26][27][28][29][30][31][32], and the detailed physical parameters required for fabricating an effective nozzle have not been reported.…”