A Laboratory Study of Rock Breakage by Rotary Drilling

Abstract

Published in Petroleum Transactions, AIME, Volume 216, 1959, pages 92–97. Abstract The effects of drilling variable on rotary drilling rates and efficiencies have been studied by a series of laboratory drilling tests. Two-cone 1.25-in. diameter bits were used to drill vertically upwards into rock samples at controlled weights and rates of rotation. Shale, sandstone and specially prepared concrete samples were used in this study. Power input to the drilling system was measured and drilling chips collected for energy-size reduction studies. Reasonably good correlations between drilling variables and rates of penetration were found. Quantities that are difficult to evaluate include rock strength parameters and the effects of bit wear. Effects of bit size and geometry require further investigation. Analysis of the drilling chips confirmed the premise that, for rocks containing two or more mineral constituents of different strengths, a greater amount of rock breakage occurs in the weaker constituent. Drilling conditions which required greater amounts of energy produced finer drilling chips. As bit tooth wear progressed, drilling chips became finer. Efficiency of rotary drilling as a rock breakage mechanism was extremely low. Comparison was made with theoretical energy requirements and with energy requirements for size reduction by comminution methods.