BIT-ROCK INTERACTION FORCES IN COMPUTER-AIDED SIMULATION OF DRILLSTRING DYNAMICS
Models of bit-rock interaction forces in computer-aided simulation of drilling process dynamics are considered in the paper. The torque on bit (TOB) model with sticking and sliding modes is described in details and can be used for analysis of self-excited stick-slip oscillations of drilling process dynamics. Stationary models can be used in the dynamic model of TOB, in particular the specific torque value as well as the Warren’s model for a roller-cone bit. An alternative Tucker-Wang TOB model is considered as well for simulation of self-excited oscillations. A simple force on bit model is presented by a viscous-elastic force model with additional optional harmonic and stochastic oscillations. Lateral forces can be added as harmonic and stochastic time functions which parameters are identified from experimental data.A considerably more complicated RGF model of drag bit-rock interaction is presented. The RGD model takes into account coupling between axial and torsional bit motions and allows studying the bit bounce with impacts.An advanced roller-cone bit model based on single indentor interaction with the rock is proposed in the paper.A 1 km drillstring is used for simulation of stick-slip oscillations and vibrations in a curved borehole as examples of application of the described force models.The discussed models are implemented in the Universal Mechanism software.