ABSTRACT
Of the many facets of rock mechanics, the more important ones in the context of drilling are concerned with rock properties such as hardness and abrasiveness, rock structures and water flow. The rock properties which most influence drillability are hardness, abrasiveness, toughness, grain size, fissility and water discontinuities. A number of methods are in use for determination of hardness and abrasiveness of rocks. The methods suggested by the International Society for Rock Mechanics, are recommended. An improvement in interpretation of the Schmidt Rihand Hardness index as determined by the method suggested by the International Society for Rock Mechanics has been suggested by R. M. Goktan and C. Ayday. In sedimentary rocks it would be correct to regard the strength of the bond as a measure of toughness, and limit hardness to the true hardness of the minerals.
