A Rock Drillability Index

MANY SYSTEMS HAVE PREVIOUSLY BEEN PROPOSED FOR DETERMINING THE "DRILLABILITY" OF ROCK. THESE SYSTEMS HAVE CONSIDERED ONLY ONE METHOD, AND SOME SYSTEMS HAVE A LIMITED OF ROCK HARDNESS. THE ROCK DRILLABILITY INDEX PROPOSED INCORPORATES THE THREE MAJOR DRILLING SYSTEMS-ROTARY, PERCUSSIVE, AND ROTARY-PERCUSSIVE-AND CONSIDERS THE COMPLETE RANGE OF ROCK TYPES FROM THE VERY SOFT, HIGHLY ALTERED ROCKS TO THE EXTREMELEY HARD TACONITES. THE DRILLABILITY INDEX IS BASED ON THE PENETRATION RATE ACHIEVED BY A 3/4-INCH DIAMETER BIT DRILLING A HOLE 4 INCHES DEEP. A ROCK ABRASIVE INDEX IS ALSO PROPOSED, AND IS BASED ON THE CHANGE IN AREA OF THE BIT CUTTING-EDGE PROFILE. DRILLABILITY AND ABRASIVE INDICES HAVE BEEN DETERMINED FOR 98 ROCK TYPES. PHYSICAL PROPERTIES OF THESE TYPES HAVE BEEN OBTAINED IN ORDER TO ASCERTAIN ANY CORRELATIONS BETWEEN THE DRILLABILITY INDICES AND THESE PROPERTIES. /AUTHOR/