DRILLING DETRITUS AND THE OPERATING PARAMETERS OF THERMALLY STABLE PDC CORE BITS

A single rock type was drilled using two types of thermally stable pol ycrystalline diamond compact (PDC) and an impregnated diamond core bit using a fully instrumented laboratory drilling rig at a fixed rotatio nal speed, and over a range of weights on bit (WOB). Operating paramet ers of the bits such as WOB, rate of penetration (ROP), rotational spe ed (RPM), torque and drilling specific energy (SE) were continuously m onitored during the drilling trials. The effects of these parameters o n the performance of the bits were examined. Relations between the dri lling variables are also described. At each set WOB for each bit, the drilling detritus were collected. The detritus sizes between 1180 and 53 microns were analysed using wet sieving and sub 53 micron was analy sed using a Malvern particle size machine. Both data were combined to obtain a particle size of the drilling detritus and operating paramete rs, cutter size and wear of the PDC and impregnated diamond core bits, and original rock grain size were established. An increase in WOB, RO P, wear rates, pins or diamond size increased the drilling detritus si ze for the bits. No relation was found between the drilling detritus a nd the rock grain size due to the regrinding effect and the high propo rtion (>30%) of matrix material in the rock. (C) 1997 Elsevier Science Ltd.