Prediction of Rock Strength from Mechanical Data of Drilling

摘要

Many studies of the last several decades have investigated the uniaxial compressive strength (UCS) of rock using drill performance parameters. However, most such studies lack theoretical value because they used experimental methods to derive empirical equations describing the relations among UCS and mechanical data. Their prediction necessarily depends on the researchers' experience. Herein, an in-situ method is proposed for evaluating UCS of rocks based on analytical models. First, an analytical model to describe rock-drilling processes using drag bits and rotary drills is described. According to this model, the drilling torque is proportional to UCS when the penetration rate is constant. Second, a concept of effective specific energy is defined. Theoretical analyses demonstrate that the effective specific energy is independent of the drill depth. Therefore, it is useful as an index reflecting rock properties. Third, the results of some laboratory tests qualitatively demonstrate the correctness and effectiveness of the proposed model. Finally, using the data of some field experiments, a method is discussed for removing the component of useless drilling torque and for calculating the effective specific energy. Results demonstrate the feasibility of the proposed method for evaluating UCS from specific energy.