Linking microearthquakes to fracture permeability change: The role of surface roughness

Despite its importance, the relation between microearthquakes (MEQs) and changes in hydraulic properties during hydraulic stimulation of a fractured reservoir has rarely been explored, and it is still not well understood. To investigate this relation, we first formulate a plausible scale dependence, where fracture length and shear displacement are variables, for channeling flow through heterogeneous aperture distributions for joints and faults. By combining this formulation with the concept of the seismic moment, we derive quantitative relations between the moment magnitude (M_w) of MEQs and the fracture permeability change in the directions orthogonal to (k_fault,⊥/k_joint) and parallel to (k_fault,∥/k_joint) the shear displacement, in the form (Formula presented.) and (Formula presented.). Despite the simplicity of the derivation, these relations have the potential to explain the results of field experiments on hydraulic stimulation, such as the enhanced geothermal systems at Soultz-sous-Fôret and Basel.