Abstract:The rock drillability is an important index for optimizing the selection of drill bit. A new methodology for evaluating rock drillability by acoustic velocity of cutting is developed,which can easily and continuously provide drillability information of stratum. The feasibility of the measurement on rough rock fragments of very small dimensions and the correlativity between acoustic velocity of cutting and rock drillability index are investigated. The results show that the acoustic velocity obtained from small cuttings is well related to rock drillability index. The relation model between the index and the acoustic velocity is developed. Test drilling is performed and shows that this method is effective.