Drilling Response of Impregnated Diamond Bits: An Experimental Investigation

The use of impregnated diamond (ID) bits has dramatically increased in hard and abrasive drilling environments over the last few decades. Although frequently used, the drilling performance of ID bit is still quite volatile and inconsistent. The dissipation of energy at the bit/rock interface is postulated as a combination of two independent processes: pure cutting or fragmentation and friction across wear surfaces. In order to better understand the mechanisms governing the bit/rock interaction, it is necessary to isolate the processes mobilised across the interface. This paper deals with the steady-state drilling response of ID bits, also called "stationary" response, in other words, the relationship between forces acting on the bit and depth of cut under conditions of constant wear state. A series of tests is performed with crowns/segments and bits on four different granites and one sedimentary limestone, using two kinematic controlled drilling rigs. The results have shown that the cutting response varies through three linear regimes that are characterised by different dominant mechanisms acting at the interface. The results also indicate how the micro-properties of the rock such as mineralogy and the segment properties (matrix hardness, wear status, concentration and diamond size) affect the response.