The Disc Bit – A Tool for Hard Rock Drilling

Abstract

Abstract This paper traces the development of a radically different design of drill bit; its concept, laboratory work and the latest field trials are described. The technology of the Disc-bit is based upon the single rolling disc cutter. This type of cutter was successfully used in rock for the first time on a tunnel boring machine in 1956. By the early 1970's, virtually every rock tunneling machine in the world had moved from picks, tungsten carbide button cones, or multi-row tapered cutters, to the single row disc. By then, the superior performance on tunneling machines had been demonstrated by practical experience in the field. Further, Colorado School of Mines (CSM) began scientific studies, and based on full scale laboratory testing, published data comparing the Specific Energy of Excavation of various tools. This clearly showed that the single row disc cutter required less energy to excavate a given volume of rock. With energy at the cutting face always a limited commodity, a lower energy requirement translated to higher penetration rate. Not until the mid 1990's was the concept of the single rolling disc cutter applied to drill bits. Very small, 3 ¼" Mini-DiscTM cutters were evaluated at CSM and found to be extremely efficient and sufficiently robust to be used on drill bits as small as 7 7/8". The U.S. Gas Research Institute sponsored an effort to develop the concept by laboratory and field testing. Other field trials were sponsored by private and government grants including the most recent test funded by a JIP, managed by PETROBRAS. An evaluation of an 8 ½" Disc-Bit was performed at GRI Catoosa Test Facility, in Oklahoma, USA.