CUTTING EXPERIMENTS USING A ROTATING WATER JET IN A BOREHOLE.

An experimental hydraulic jetting device intended to operate in a 16-in-diam borehole was designed, fabricated, and used to cut coal and simulated coal samples. This device consisted of two 0. 107-in-diam nozzles that rotated in a plane perpendicular to a 50-inch length of high-pressure tubing. Experiments were also conducted with stationary jets issuing from a single 0. 142-in-diam nozzle. Numerous experiments were performed using systematic variations of jet parameters coupled with assessments of cutting rates. Tests showed that when operated at 4,000 psi pressure and a 40-gpm flow rate (1) the device can fragment coal up to a distance of 8 feet from the nozzle, (2) 4,000-psi jets cut more effectively than lower pressure jets with the same nozzle diameter, (3) stationary jets do not cut as effectively as moving jets, (4) interkerf breaking occurs when the kerf spacing is less than 2 inches, and (5) if the kerfs are spaced less than 1/2 inch, the jet is deflected and thereby reduces cutting effectiveness.