Summary

Understanding the failure mechanisms that govern fracture propagation in
layered rocks is essential for predicting fracture geometry and optimizing subsurface
operations. This study presents a phase-field modeling framework to
systematically investigate the effects of stiffness contrast, fracture energy
release rate, and in-situ stress on quasi-static fracture propagation around
pressurized cavities embedded in layered rock systems. A modified strain
energy decomposition scheme is introduced to distinguish between tensile
(Mode I) and shear (Mode II) failure, which makes it possible to effectively
capture mixed-mode fracture patterns. Simulation results reveal several key
insights: (1) In homogeneous media, localized fractures that initiate from a
pressurized cavity propagate in Mode I, while deviatoric strain energy may
lead to extensive partially damaged zones under high compressive in-situ
stresses; (2) Material heterogeneity, particularly variations in Young’s modulus
and shear fracture energy release rate, significantly influences fracture
paths, branching, and transitions in failure mode; (3) In rock masses that
contain a soft and weak interlayer (similar to a vein), high stiffness contrast
and low shear resistance in the thin interlayer can trigger fracture bifurcation
and lead to shear-dominated branch formation within the interlayer. This
study provides mechanistic insights into fracture deflection, arrest, and bifurcation
phenomena that are critically important, yet often inadequately
captured by conventional modeling approaches.