Polycrystalline diamond compact (PDC) bits, which are widely used in oil and gas well drilling, have begun to be used in geothermal well drilling. Mitsubishi Materials Corporation, K. Maikai Co., Ltd, and National Institute of Advanced Industrial Science and Technology started collaborative research project commissioned by Japan Organization for Metals and Energy Security with the aim of development of PDC bits that have satisfying efficiency to drill hard, inhomogeneous and fractured formations as is common in the geothermal fields. In the present report, the outline of the project is provided, including the development of PDC cutters and bits and the performance evaluation of PDC bits through laboratory and field drilling tests. Three predetermined numerical goals concerning the drilling performance, namely drilling speed, bit life, and gage loss, were achieved in the project. The ROP model proposed by Miyazaki et al. (2022), which was constructed based on a series of laboratory drilling tests under controlled conditions conducted as part of the project, is also reviewed. The model considers the effect of bit wear quantitatively and has an extremely simple form compared with earlier models. The applicability of the model to field drilling data and several future issues are also discussed.
