Hydro-shearing and traffic light protocols in mitigating seismic risks: A fully-coupled poroelastic boundary integral modeling approach

In low-permeability geothermal reservoirs, hydro-shearing of pre-existing natural fractures plays a crucial role in improving connectivity between injection and production wells, thereby enhancing heat extraction efficiency. This process increases fracture conductivity through dilation caused by injection-induced slip; however, it also carries the risk of inducing seismic events, posing significant challenges for geothermal operations. This study employs a coupled hydro-mechanical numerical model based on the boundary element method to simulate hydro-shearing under two distinct fluid injection scenarios: (1) monotonic injection and (2) cyclic injection regulated by a traffic light system (TLS). The model assesses the effectiveness of these injection regimes in enhancing fracture conductivity while mitigating seismic hazards. Results indicate that monotonic injection frequently triggers a cascade of seismic events, disrupting pressure and stress distributions on nearby faults and resulting in complex seismic and aseismic interactions. In contrast, TLS-regulated cyclic injection, when carefully managed, promotes stable slip behavior and improves fracture conductivity. This approach proves particularly effective over extended durations during the simultaneous stimulation of two parallel faults. However, in multi-stage stimulation scenarios—where natural fractures are stimulated sequentially—TLS-based cyclic injection, while more efficient at enhancing conductivity, may increase seismicity risk with prolonged application, thereby limiting its safe operational window.