Laboratory Testing of Percussion Drills for Geothermal Applications

Laboratory tests of percussion drilling tools which were done at Drilling Research Lab, Salt Lake City, during February 1980, are described. The purpose of the tests was threefold: (a) to compare the parenetration rates of different hammers with each other and with conventional rotary drilling; (b) to measure and compare the hammer pulses at normal and high temperatures; and (c) to establish hammer life and failure modes at high temperature. Two roller bit hammers and three solid bit hammers were tested. All exhibited much higher rates of penetration in granite than were obtained with conventional rotary techniques. Tests at high temperature revealed several failure modes for the air driven hammers. Minor modifications should allow operation of these hammers at high temperature.