Theory and approach of identification of ground interfaces based on rock drillability index

Abstract

Rock drillability index is a very key parameter in selection of drill bit type and determination of productivity in petroleum, mining and geology. Unfortunately, there are many limits in the current definition as well as experimental methods. Drillability is redefined and a new concept of drillability index is brought out from analysis. Under the new concept, the drillability index is defined as penetration rate under specific energy. Based on the coupling relationship among effective thrust, rotation speed, penetration rate and drillability index, a calculation formula is established. Besides, the sensitivity of the drillability index in identification of ground layer is analyzed and its physical signification is expatiated also. The result shows that the new index overcomes the blind area in the traditional concept and can be used in continuous identification of ground layer along borehole profile.