Effect of confining pressure on the axial impact pressure of hydraulic jetting

Hydraulic jetting techniques have found growing application in improving the rate of penetration (ROP) and enhancing oil recovery (EOR) in the oil and gas field. But it always encounters high confining pressure condition which may significantly weaken the performance of hydraulic jetting at the bottom of wells especially for the deep and ultra-deep wells, so it is crucially important to study the effect of the confining pressure on the high pressure jetting. A hydraulic jetting impact pressure measuring device which could generate low confining pressure ( < 10MPa) is used to measure the jet pressure and axial impact pressure. Results show that, with the method to build the confining pressure by changing the diameter of the outlet, the dimensionless jet pressure hardly changes until the dimensionless confining pressure exceeds a threshold which approximately equals to the square of the nozzle discharge coefficient, and from then on it increases with the confining pressure linearly; the confining pressure has no effect on the axial impact pressure within one nozzle diameter standoff distance; numerical fitting analysis show that the dimensionless axial hydrostatic pressure is proportional to the 3.3 power of the dimensionless confining pressure, and increases linearly with the dimensionless standoff distance; the dimensionless axial impact pressure is inversely proportional to the 0.15 power of the dimensionless confining pressure, and decreases linearly with the dimensionless standoff distance; but if the dimensionless confining pressure exceeds a threshold value which is between 0.6 and 0.7 in our study, the axial hydraulic static pressure will be in accord with the confining pressure, and the axial impact pressure won't change. This study provides helpful instruction for the hydraulic factor design for drilling, sand-flushing operation, et al.