Experimental study on identification of layered rock mass interface along the borehole while drilling

In this paper, the response characteristics of parameters along the borehole while drilling to rock mass interface are experimentally studied by drilling method. Using the developed measurement while drilling (MWD) system, drilling experiments were carried out on granite, limestone, and sandstone composite rock masses, and real-time monitoring of parameters while drilling, i.e., rotary speed, drilling depth, feed force, and drilling torque, were carried out during the drilling process. The results show that the developed measurement system operates stably and monitors well, and the response characteristics of drilling speed, feed force, and drilling torque at the rock layer interface are obvious, which lays a foundation for the identification of lithology while drilling. There is no obvious change in the rotary speed while drilling, which can be set as a constant. The rate of penetration is the most sensitive parameter while the rock structure changes, followed by the feed force. With the increase of the rotary speed, the sensitivity of the feed force to the response of the rock structure interface will increase accordingly. The drilling torque fluctuates greatly in the rock structure, and the bit torque at different rotary speeds shows different variation laws in the drilling process of different rock structures, but it still has a clear response to the rock stratum interface. The comprehensive analysis of multiple sets of parameters shows that the use of parameters along the borehole while drilling can effectively realize the accurate identification of the layered rock mass interface.