Modelling fluid injection-induced fracture activation, damage growth, seismicity occurrence and connectivity change in naturally fractured rocks

• Published in: International journal of rock mechanics and mining sciences (Oxford, England : 1997) England : 1997), 2021-02, Vol.138, p.104598, Article 104598
• Main Authors: Lei, Qinghua, Gholizadeh Doonechaly, Nima, Tsang, Chin-Fu
• Format: Article
• Language: English
• Subjects: Computational fluid dynamics; Connectivity; Crack propagation; Earthquake damage; Enhanced geothermal systems; Evolution; Finite element method; Fluid flow; Fluid injection; Fracture network; Fractures; Geoengineering; Geomechanics; Hydraulic stimulation; Hydro-mechanical coupling; Induced seismicity; Injection; Mathematical models; Mechanical properties; Numerical models; Percolation; Permeability; Pore pressure; Pore water pressure; Porous media; Rock masses; Rocks; Seismic activity; Seismicity
• ISSN: 1365-1609; 1873-4545; 1873-4545
• DOI: 10.1016/j.ijrmms.2020.104598

We develop a fully-coupled hydro-mechanical model to simulate fluid injection-induced activation of pre-existing fractures, propagation of new damages, development of seismic activities, and alteration of network connectivity in naturally fractured rocks. The natural fracture system is represented by a discrete fracture network. The stress and strain fields of the fractured porous media are solved in the framework of a finite element model, which mimics the damage evolution in rock matrix based on an elasto-brittle failure criterion and simulates the normal/shear displacement of natural discontinuities based on a non-linear constitutive law. The coupled geomechanics and fluid flow processes in the fractured rock are computed honouring essential coupling mechanisms such as pore pressure-induced shear slip of pre-existing fractures, poro-elastic response of rock matrix, and stress-dependent permeability/storativity of both fractures and rocks. We use the numerical model developed to investigate the hydro-mechanical behaviour of two cases of deeply buried fractured rock in response to high-pressure fluid injection, one case with fracture density just below the percolation threshold and the other above the threshold. We observe a strong control of natural fracture network connectivity on the damage emergence, seismicity occurrence and connectivity change in the rock mass subject to hydraulic stimulation. We also highlight the strong poro-elastic effect that tends to drive heterogeneous connectivity evolution of fracture systems during fluid injection. The results of our research and insights obtained have important implications for injection-related geoengineering activities such as the development of enhanced geothermal systems and extraction of hydrocarbon resources.