Simulation of Hydraulic Fracturing Under Brittle-Ductile Transition Condition with Bond-Degradation Approaches

Abstract

Summary The hottest topic in geothermal energy development is the realization of enhanced geothermal systems in the ductile zone. The extraction of thermal energy may require from the surrounding rocks that may require hydraulic fracturing through rocks in the ductile zone. One of the key factors for the realization is, therefore, rock behaviour under high pressure and temperature conditions, where rocks are assumed to ductile materials. Though distinct element method is frequently used to understand failure mechanism of rock, hydraulic fracturing simulations including brittle-ductile transition has not been fully investigated. Considering fracture patterns and deformation of granite show drastic changes between brittle and ductile or at their transition, installation of the transitional behaviours is indispensable. In this study, hydraulic fracturing simulations with the degradation approaches, i.e. a bi-linear approximation model and a degradation model, to replicate semi-brittle or ductile behaviour at high temperature and confining pressure were demonstrated. The numerical simulation results showed that a bi-linear approximation model, which is suitable for replicating ductile behaviour of granite, gives the results consistent with the actual laboratory experiments under high temperature and confining pressure conditions. Moreover, it is indicated that joint modelling of both models could be useful to reproduce brittle-ductile transitional behaviours.