Formation Fracturing by High-Energy Impulsive Mechanical Loading

Abstract

AbstractRecent technological advances to trigger high-energy seismic waves from within the wellbore have spurred interest in their application to induce fracturing. While a considerable body of recent experiments at the bench scale (on the order of 1 cubic foot) show promise, there remains considerable uncertainty in how the process scales. This work characterizes the scaling relationships between the extent and intensity of fracturing stimulation and stress-wave characteristics. Our approach leverages direct numerical simulation of the elastodynamic equations accounting for nonlinear fracture mechanics. We apply a hybrid Finite-Discrete Element Method (FDEM) where cohesive (elasto-plastic) laws hold mesh elements together until complete failure. Beyond failure, elements act as deformable free bodies that can interact via contact constraints. An infinite domain is modeled with a spherical inclusion within which an impulsive load is imposed. The dynamic load models a rise time to a peak pressure, followed by a decay period, and all occurring within micro- to milliseconds. The model is validated with experimental observations at the bench scale after mesh-refinement verification. Finally, the model is used to explore the dimensionless parameter space by varying loading characteristics (rise time, peak pressure, and impulse) to reveal the stimulated damaged bulk volume and the crack intensity within it. At the bench scale, the model reproduces a nearly linear trend between damage radius and peak stress. Beyond that, however, the model predicts that this scaling slows considerably to a fractional power law between the damaged radius and the peak stress. This limitation is coincident with a geometric increase in the intensity of damage within the stimulated volume.