Adaptive modeling of rock crack mechanism during drilling operation based on modified peridynamics

Abstract

In this paper, an efficient adaptive model is developed to simulate the rock crack mechanism during drilling operation based on a three-dimensional modified peridynamics. The modified peridynamics equation defines the micro-bond force as the combination of a normal part, which comes from the tensile deformation, and a tangential part, which comes from the shear deformation. The bond break criterion is set to include both the tensile deformation and the shear deformation. By redefining the local damage criterion and the bit penetration criterion, this model iterates adaptively with crack propagation and drill bit penetration. Penetration rates under different drilling conditions are investigated, including weight on bit, rotary speed, axial vibration frequency and amplitude. This approach takes advantages of the peridynamics in solving discontinuity involved problems, and successfully applies peridynamics to drilling modeling. As a consequence, the damage propagation of rock is automatically captured. Another advantage of this approach comes from the application of the modified peridynamics, where the shear deformation and its related damage are considered separately in the constitutive relation. This is crucial for drilling modeling because the rotation of drill bit often introduces large amounts of tangential cracks. Finally, the proposed model is adaptive and quite efficient, thus, this approach can be used to model the complete drilling process with a large depth.