Fluid-Induced Fracturing of Initially Damaged Granite Triggered by Pore Pressure Buildup

Abstract

Fluid flow-induced seismic activity has been observed in various environments; however, the relations among fluid migration, pore pressure buildup, and fracturing remain poorly understood. In the present study, we conducted fluid-induced fracture experiments on initially damaged granite. Acoustic events and macroscopic failure of the samples were triggered exclusively by a buildup of pore pressure, and fracturing occurred when the average effective stress reached a critical stress state (following the Mohr-Coulomb criterion). The spatiotemporal distribution of acoustic events is mainly controlled by the pore pressure diffusion front through the sample. Fluid migration velocity was dependent primarily on the initial stress state and permeability. Although the propagation of acoustic events was slower in our laboratory experiments than in natural seismic swarms, a similar parabolic relationship in space and time suggests that these microearthquakes are likely triggered by the passage of a critical pore fluid pressure through the damaged zones.