Hydroshearing Stimulation: Fracture Slip & Induced Seismicity

Injection Controls

Wellhead pressure ΔP 0.0 MPa

Differential stress σ₁−σ₃ 20.0 MPa

Friction coefficient μ 0.60

Stimulation Status

GREEN — safe to inject

Pressure front R(t)

0 m

Fractures slipped

0 / 0

Cumulative seismic moment ΣM₀

0 N·m

Largest event

Mw —

How it works

Enhanced geothermal systems (EGS) create permeability not by tearing new rock (tensile hydrofracturing) but usually by hydroshearing: raising fluid pressure inside pre-existing, critically-oriented fractures until they slip in shear. Slip permanently increases fracture aperture, boosting permeability with almost no fluid loss to matrix rock.

For a fracture at angle θ to the maximum principal stress σ₁, the Mohr-Coulomb stresses resolved on its plane are:

σn(θ) = (σ1+σ3)/2 + (σ1-σ3)/2 · cos(2θ)
τ(θ)  = (σ1-σ3)/2 · sin(2θ)

Injecting fluid raises pore pressure P inside the fracture, which lowers the effective normal stress clamping it shut. Frictional slip (for a cohesionless, pre-existing fracture) triggers when:

τ(θ) ≥ μ · (σn(θ) − ΔP)

Each slip event radiates a small earthquake. Treating the slipped patch as a circular crack of radius a with stress drop Δτ, its seismic moment and moment magnitude are:

M0 = (16/7) · Δτ · a³
Mw = (2/3) · log10(M0) − 6.07

Wellhead pressure — raises pore pressure; a diffusive front spreads outward from the well and only fractures inside it feel the pressure rise.
Differential stress — higher σ1−σ3 means more fractures are already close to Coulomb failure, so slip (and seismicity) starts at lower injection pressure.
Friction coefficient μ — most crystalline basement rock follows Byerlee's law, μ ≈ 0.6–0.85; lower μ makes fractures easier to reactivate.
Traffic light — real EGS projects (Basel 2006, Pohang 2017) throttle or stop injection once induced-event magnitude crosses a threshold. This sim uses simplified illustrative thresholds: green Mw<1.0, amber 1.0–2.0, red >2.0 (stop).

Stable fracture Near critical Slipped (seismic event) Injection well

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