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Description
Fluid injection into fractured reservoirs can produce either clustered or front like induced seismicity, yet the controlling role of fracture network parameters remains poorly understood. This study uses a fully coupled hydro mechanical (HM) model in combination with the discrete fracture network (DFN) approach to quantify how fracture length scaling, density, and connectivity (as represented by the percolation parameter) govern pressure diffusion, damage, slip, and seismic migration.
Fractures follow a power law length distribution with exponents 1.5–3.0 and intensities 0.2–0.4 m⁻¹, yielding values of percolation parameter χ that span from disconnected (χ < 5) to well connected (χ > 7) regimes. The rock matrix is represented by an elasto brittle poroelastic damage model, and fractures exhibit nonlinear normal closure, stress dependent permeability, and elasto plastic shear with dilation. Flow in fractures and matrix is solved within a poromechanical framework, and induced events are reconstructed from damage and slip related seismic moments.
Constant rate injection produces two end member behaviors. In low χ networks, sharp pressure build up and subsequent drops accompany intermittent hydraulic linkage between clusters, leading to broad matrix pressurization, extensive wing crack damage, and spatially clustered seismicity tied to localized overpressure and Coulomb failure stress hotspots. In highly connected networks, pressure remains elevated with damped oscillations, flow is channeled along a percolating fracture backbone, rock damage is limited, and seismicity organizes into a coherent, radially migrating front that exhibits super diffusive migration relative to classical diffusion.
Slip related magnitudes scale with fracture length, with steeper length–magnitude slopes in sparse networks where slip localizes on few long fractures. These findings link fracture network parameters to seismicity patterns and offer useful insights for tailoring stimulation strategies that would enhance connectivity while constraining seismic hazard in enhanced geothermal systems (EGS) and other subsurface operations.
| Country | Sweden |
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