WEAR CHARACTERISTICS OF PDC PIN AND HYBRID CORE BITS IN ROCK DRILLING

Drilling cost is controlled to a large extent by the drilling rate which is heavily influenced by the wear condition of the bit. Developments in polycrystalline diamond compact (PDC) production techniques have enabled the manufacture of rectangular ''pins'' of material which have been incorporated into various forms of core bits. The wear characteristics of these bits are controlled by a range of factors, however, the principal factors which need to be considered in predicting wear rates are the bit, the bit operating parameters and the characteristics of the penetrated rock. A variety of rock types were drilled using two types of PDC (pin and hybrid) and impregnated diamond core bits using a fully instrumented laboratory drilling rig at different rotational speeds and over a range of weights on bit. A wide range of textural, mechanical and intact properties of the rocks were quantitatively determined. Wear (Weight loss and height loss) of each bit were measured after a series of holes were drilled in each rock type. The wear of PDC bits can take many forms, however, the most common wear mechanism operating on PDC bits during rock drilling is abrasion. Impact loading and impact fatigue also accelerates the wear of bits. The effects of the rock properties and the operating parameters on the wear performance of the bits were examined. Total silica content, grain shape factor, Moh's and Shore hardness, and abrasivity indexes were found to have most influence on the wear rate of the bits. A reduction in rotational speed led to an increase in wear rate with less than optimal performance of the bits. The abrasive wear volume loss is linearly proportional to the WOB and torque.