Hydraulic stimulation is a key method for creating permeable pathways in deep geothermal systems, where natural fracture networks are often too tight to allow economic fluid circulation. The effectiveness of stimulation depends on the ability to enhance permeability through shear slip on pre-existing discontinuities, while field operations are challenged by complex fluid-fault interactions and the frequent occurrence of injection-induced seismicity. A mechanistic understanding of how aseismic slip propagates and modifies permeability is therefore essential for designing effective and safe stimulation strategies.
This thesis investigates fluid-driven aseismic rupture with particular emphasis on shear-induced dilatancy, permeability evolution, and the role of the stress field. We begin with a semi-analytical treatment of rupture growth under a linear stress gradient, the first problem addressed in this work. This analysis provides fundamental insight into how in-situ stress variations influence the extent and asymmetry of fluid-driven slip.
We then employ a recently developed hydro-mechanical solver that models a poroelastoplastic interface with Mohr-Coulomb strength, slip-weakening friction, non-associated dilatancy, nonlinear contact response, and aperture-dependent permeability. After verifying the solver against semi-analytical benchmarks, we apply it to the Basel-1 geothermal stimulation. Using the recorded injection schedule together with geological and stress constraints, we reproduce both the wellhead pressure evolution and the migration of the dominant microseismic cluster. The analysis highlights how permeability increase due to dilation, nonlinear contact compliance, and variable permeability are required to reconcile observed pressure drops and rupture expansion.
Finally, we extend the theoretical understanding of fluid-driven aseismic slip by embedding dilatancy-controlled permeability evolution into a two-dimensional plane-strain formulation. The analysis identifies a new early-time diffuse-dilatant regime, arising from shear-induced dilatancy documented in laboratory experiments and rupture theory, in which rupture propagation is slowed, overpressures are depressed near the injection point, and self-similarity is lost compared to constant-permeability theory. A transition occurs once slip reaches the critical dilatancy distance, leading to faster growth and, in critically stressed cases, undrained pore-pressure drops. At late times, dilatancy localizes into a narrow process zone, and the solution converges toward the self-similar form predicted by abrupt-dilatancy theory. This framework clarifies the regimes where dilatant hardening is most influential and the well-pressure signatures by which it may be detected in the field.
This doctoral research provides a quantitative and conceptual framework for interpreting hydraulic stimulation data and for designing injection protocols that promote stable hydro-shearing and sustained
