Stress‐Dependent Microcrack Evolution and Damage Constitutive Model of Low Permeability Sandstone

To identify the fracture initiation position and growth characteristics in heterogeneous rock, we performed in‐situ NMR observations to capture fracture propagation and proposed a damage constitutive model considering crack closure to characterize the macroscopic failure behavior of rock. Results reveal that microcrack propagation is earlier in the area with high microcrack density. Fractures initiate from pores and propagate between pores along the direction of maximum compressive stress loading. Fracture propagation tends to coalesce and form a larger fracture cluster in the zone with high microcrack density, showing a remarkable fracture localization. In contrast, a dispersed crack growth occurred in areas with low density. The proposed damage constitutive model considering crack compaction effectively characterizes the rock's prefailure process. These results clarify the mesoscopic fracture propagation within the porous rock considering internal microcrack distribution, which has significant implications for predicting fracture growth within rocks.