Postinjection Normal Closure of Fractures as a Mechanism for Induced Seismicity

Understanding the controlling mechanisms underlying injection-induced seismicity is important for optimizing reservoir productivity and addressing seismicity-related concerns related to hydraulic stimulation in Enhanced Geothermal Systems. Hydraulic stimulation enhances permeability through elevated pressures, which cause normal deformations and the shear slip of preexisting fractures. Previous experiments indicate that fracture deformation in the normal direction reverses as the pressure decreases, e.g., at the end of stimulation. We hypothesize that this normal closure of fractures enhances pressure propagation away from the injection region and significantly increases the potential for postinjection seismicity. To test this hypothesis, hydraulic stimulation is modeled by numerically coupling flow in the fractures and matrix, fracture deformation, and matrix deformation for a synthetic reservoir in which the flow and mechanics are strongly affected by a complex three-dimensional fracture network. The role of the normal closure of fractures is verified by comparing simulations conducted with and without the normal closure effect.

[1]  R. J. Pine,et al.  A hydro-thermo-mechanical numerical model for HDR geothermal reservoir evaluation , 1996 .

[2]  Julian J. Bommer,et al.  Induced seismicity associated with Enhanced Geothermal Systems , 2007 .

[3]  Valentin Gischig,et al.  The importance of earthquake interactions for injection‐induced seismicity: Retrospective modeling of the Basel Enhanced Geothermal System , 2016 .

[4]  Eirik Keilegavlen,et al.  A finite-volume discretization for deformation of fractured media , 2018, Computational Geosciences.

[5]  L. Durlofsky,et al.  An Efficient Discrete-Fracture Model Applicable for General-Purpose Reservoir Simulators , 2004 .

[6]  J. Rice.  Spatio‐temporal complexity of slip on a fault , 1993 .

[7]  Generation of large postinjection‐induced seismic events by backflow from dead‐end faults and fractures , 2015 .

[8]  Hiroaki Niitsuma,et al.  Microseismicity and permeability enhancement of hydrogeologic structures during massive fluid injections into granite at 3 km depth at the Soultz HDR site , 2004 .

[9]  Thomas Kohl,et al.  Predictive modeling of reservoir response to hydraulic stimulations at the European EGS site Soultz-sous-Forêts , 2007 .

[10]  R. Horne,et al.  Investigation of injection-induced seismicity using a coupled fluid flow and rate/state friction model , 2011 .

[11]  Christophe Geuzaine,et al.  Gmsh: A 3‐D finite element mesh generator with built‐in pre‐ and post‐processing facilities , 2009 .

[12]  Eirik Keilegavlen,et al.  Three-Dimensional Numerical Modeling of Shear Stimulation of Naturally Fractured Rock Formations , 2017 .

[13]  Markus Häring,et al.  Characterisation of the Basel 1 enhanced geothermal system , 2008 .

[14]  J. Nordbotten,et al.  Finite volume methods for elasticity with weak symmetry , 2015, 1512.01042.

[15]  Jan M. Nordbotten,et al.  An efficient multi-point flux approximation method for Discrete Fracture-Matrix simulations , 2012, J. Comput. Phys..

[16]  Stefan Wiemer,et al.  The role of Coulomb stress changes for injection‐induced seismicity: The Basel enhanced geothermal system , 2013 .

[17]  Isabelle Lecomte,et al.  Monitoring of induced seismicity during the first geothermal reservoir stimulation at Paralana, Australia , 2014 .

[18]  C. Dinske,et al.  Pore pressure behavior at the shut‐in phase and causality of large induced seismicity at Basel, Switzerland , 2017 .

[19]  N. Barton,et al.  The shear strength of rock joints in theory and practice , 1977 .

[20]  J. Nordbotten.  Cell‐centered finite volume discretizations for deformable porous media , 2014 .

[21]  N. Barton,et al.  FUNDAMENTALS OF ROCK JOINT DEFORMATION , 1983 .

[22]  Mofazzal Hossain,et al.  A shear‐dilation‐based model for evaluation of hydraulically stimulated naturally fractured reservoirs , 2002 .

[23]  Roland N. Horne,et al.  An investigation of stimulation mechanisms in Enhanced Geothermal Systems , 2014 .

[24]  Reinhard Jung,et al.  A numerical model for fluid injection induced seismicity at Soultz-sous-Forêts , 2010 .

[25]  R. J. Pine,et al.  Downward migration of shearing in jointed rock during hydraulic injections , 1984 .

[26]  Dominique Bruel,et al.  Using the migration of the induced seismicity as a constraint for fractured Hot Dry Rock reservoir modelling , 2007 .

[27]  Stein Krogstad,et al.  Open-source MATLAB implementation of consistent discretisations on complex grids , 2012, Computational Geosciences.

[28]  Nick Barton,et al.  An improved model for hydromechanical coupling during shearing of rock joints , 2001 .

[29]  P. Segall,et al.  Injection‐induced seismicity: Poroelastic and earthquake nucleation effects , 2015 .

[30]  O. Lengliné,et al.  Seismicity related to the hydraulic stimulation of GRT1, Rittershoffen, France , 2017 .

[31]  N. Barton,et al.  Strength, deformation and conductivity coupling of rock joints , 1985 .