The design of a water jet drill for development of geothermal resources. Final report

Water jet drilling of rock is shown to be a feasible method for potential improvement in gaining access to the earth's resources. Drilling rates of up to 280 in./min in sandstone and 40 in./min in granite have been achieved. While the addition of polymers to the jet stream is found advantageous the low (15%) level of improvement and the difficulty in maintaining concentrate negated further development. The application of confining pressure was found to reduce jet performance, but this was found to be a function more of the rock response than of the jet parameters. Field tests of water jets underground indicated the jet system could be modified to cope with this change. Water jets were found to be more effective, for drilling larger holes, where a combined water jet:roller bit system was developed and laboratory and field trials of this are described. As well as determining the controlling parameters affecting jet drilling performance, and proving that rock compressive strength is not one of them, the research examined other methods of improving jet cutting performance. At jet pressures below 10,000 psi abrasive laden jets were found most advantageous while, for drilling granite, a cavitating flow proved more effective at pressures above 10,000 psi. A reason for this is postulated. Experiments to develop a standardized cavitation resistance test for rock specimens have also been undertaken