Study On The Mechanism Of PDC Drill Bit Breaking Rock Mass And The Recognition Technology Of Rock States

Boring holes, a common and effective method to prevent and control geological disasters in coal mining, is a process that contains a wealth of geological information, such as lithology, gas disaster, rock burst and so on. Unfortunately, it is very few that people has used this kind of geological information. In this paper, theoretical knowledge and numerical simulation method were used firstly to do the research of PDC bit breaking rock mass systematically, and then, basing on the characteristic of the hydraulic drilling rig used in coal mine, an equipment to monitor drilling technical parameters while the hydraulic drilling rig is working was made. Using the equipment, we have done a couple of times monitoring tests under coal mine in Shan Xi province, and data obtained from the test were analyzed carefully. To make the relationship of drilling technical parameters with geological information clear, a method to express the relationship was proposed using dimensional analysis method. Finally, numerical simulation techniques were used to verify the expression proposed above, and conclusions got are as follows:(1) Combining the utilization of elastic mechanics and the theory of contact mechanics, the relationship of pressed force with pressed depth for PDC drilling bits was obtained, the results show that: with the increase of pressed depth, the pressed force increases exponentially. To analyze the effect of pressing angle on pressed force, numerical simulation technique was used, the results show that: when the pressing angle is about 16°, the pressed force to press the same depth is the smallest force.(2) Based on the characteristic of the hydraulic drilling rig used in coal mine, an equipment to monitor drilling technical parameters while the hydraulic drilling rig is working was made, Using the equipment, we have done a couple of times monitoring tests under coal mine in Shan Xi province, and data obtain from the test were analyzed carefully, the results show that: with the increase of drilling depth, both of drilling pressure and torque on the drilling rig increase are increase. To make the relationship of drilling technical parameters with geological information clear, a method to express the relationship was proposed using dimensional analysis method, the results show that: the smaller the value of Id, the harder the rock mass is.(3) To analyze the effect of drilling speed and rotation speed on drilling pressure and torque, finite element models of PDC bit and rock mass were made and the process of PDC bit breaking rock mass was reproduction, the results show that: with the increase of drilling speed, both of drilling pressure and torque are increasing exponentially; with the increase of rotation speed, both of drilling pressure and torque are decreasing inversely. The results of research on the effect of lithology on drilling pressure and torque show that: the value of Id from numerical simulation is about one third of that from monitor tests in the field.