Experimental results on the effect of Bit wear on torque response

•The bit torque and height loss of tips on a percussion bit are closely related.•The bit torque changes with the wear of the cutters on PDC core bits.•The bit torque is useful for evaluating the tooth wear of roller cone bits.

Percussion bits, polycrystalline diamond compact (PDC) bits and roller cone bits are widely used in well drilling. The evaluation methods for downhole conditions, such as the wear condition of drill bits and the in situ rock strength, are important issues in improving the drilling efficiency and reducing the drilling cost. In this study, drilling tests were conducted in laboratory using the three types of drill bit and various types of rock. On the basis of the results, a close relation between the bit wear condition and bit torque was found for each bit.