Induced fault reactivation by thermal perturbation in enhanced geothermal systems

Geothermal energy has emerged as an alternative to ensure a green energy supply while tackling climate change. Geothermal systems extract the heat stored in the Earth’s crust by warming up water, but the low rock permeability at exploitation depths may require the hydraulic stimulation of the rock fracture network. Enhanced Geothermal Systems (EGS) employ techniques such as hydro-shearing and hydro-fracturing for that purpose, but their use promotes anthropogenic earthquakes induced by the injection or extraction of fluids. This work addresses this problem through developing a computational 3D model to explore fault reactivation and evaluating the potential for earthquake triggering at preexisting geological faults. These are included in the model as frictional contacts that allow the relative displacement between both of its sides, governed by rate-and-state friction laws and fully coupled with thermo-hydro-mechanical equations. We apply our methodology to the Basel project, employing the on-site parameters and conditions. Our results demonstrate that earthquakes which occurred in December 2006 in Basel (Switzerland) are compatible with the geomechanical and frictional consequences of the hydraulic stimulation of the rock mass. The application of our model also shows that it can be useful for predicting fault reactivation and engineering injection protocols for managing the safe and sustainable operation of EGS.

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Discrete element modeling of fluid injection–induced seismicity and activation of nearby fault

Canadian Geotechnical Journal ◽

10.1139/cgj-2014-0435 ◽

2015 ◽

Vol 52 (10) ◽

pp. 1457-1465 ◽

Cited By ~ 26

Author(s):

Jeoung Seok Yoon ◽

Günter Zimmermann ◽

Arno Zang ◽

Ove Stephansson

Keyword(s):

Shale Gas ◽

Induced Seismicity ◽

Fluid Pressure ◽

Discrete Element ◽

Fault Reactivation ◽

Fluid Injection ◽

Enhanced Geothermal Systems ◽

Discrete Element Modeling ◽

Geothermal Systems ◽

Element Modeling

Enhanced geothermal systems, shale gas, and geological carbon sequestration all require underground fluid injection in high-pressure conditions. Fluid injection creates fractures, induces seismicity, and has the potential to reactivate nearby faults that can generate a large magnitude earthquake. Mechanisms of fluid injection–induced seismicity and fault reactivation should be better understood to be able to mitigate larger events triggered by fluid injection. This study investigates fluid injection, induced seismicity, and triggering of fault rupture using hydromechanical-coupled discrete element models. Results show that a small amount of fluid pressure perturbation can trigger fault ruptures that are critically oriented and stressed. Induced seismicity by rock failure shows in general higher b-values (slope of magnitude–frequency relation) compared to seismicity triggered by the fault fracture slip. Numerical results closely resemble observations from geothermal and shale-gas fields and demonstrate that discrete element modeling has the potential to be applied in the field as a tool for predicting induced seismicity prior to in situ injection.

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