Induced seismicity in enhanced geothermal systems : assessment of thermo-hydro-mechanical effects

Micro-seismicity, and especially felt seismicity, induced by Enhanced Geothermal Systems (EGS) operations is a matter of scientific interest, not only because of the related risks and concerns, but also because the correspondence between injection and seismic activity still remains unclear. The Thes...

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Autor: De Simone, Silvia
Tipo de recurso: tesis doctoral
Estado:Versión publicada
Fecha de publicación:2017
País:España
Institución:CBUC, CESCA
Repositorio:TDR. Tesis Doctorales en Red
OAI Identifier:oai:www.tdx.cat:10803/405890
Acceso en línea:http://hdl.handle.net/10803/405890
https://dx.doi.org/10.5821/dissertation-2117-107946
Access Level:acceso abierto
Palabra clave:Àrees temàtiques de la UPC::Enginyeria civil
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dc.title.none.fl_str_mv Induced seismicity in enhanced geothermal systems : assessment of thermo-hydro-mechanical effects
title Induced seismicity in enhanced geothermal systems : assessment of thermo-hydro-mechanical effects
spellingShingle Induced seismicity in enhanced geothermal systems : assessment of thermo-hydro-mechanical effects
De Simone, Silvia
Àrees temàtiques de la UPC::Enginyeria civil
55
626
title_short Induced seismicity in enhanced geothermal systems : assessment of thermo-hydro-mechanical effects
title_full Induced seismicity in enhanced geothermal systems : assessment of thermo-hydro-mechanical effects
title_fullStr Induced seismicity in enhanced geothermal systems : assessment of thermo-hydro-mechanical effects
title_full_unstemmed Induced seismicity in enhanced geothermal systems : assessment of thermo-hydro-mechanical effects
title_sort Induced seismicity in enhanced geothermal systems : assessment of thermo-hydro-mechanical effects
dc.creator.none.fl_str_mv De Simone, Silvia
author De Simone, Silvia
author_facet De Simone, Silvia
author_role author
dc.contributor.none.fl_str_mv Carrera Ramírez, Jesús
Vilarrasa Riaño, Víctor
Universitat Politècnica de Catalunya. Departament d'Enginyeria Civil i Ambiental
dc.subject.none.fl_str_mv Àrees temàtiques de la UPC::Enginyeria civil
55
626
topic Àrees temàtiques de la UPC::Enginyeria civil
55
626
description Micro-seismicity, and especially felt seismicity, induced by Enhanced Geothermal Systems (EGS) operations is a matter of scientific interest, not only because of the related risks and concerns, but also because the correspondence between injection and seismic activity still remains unclear. The Thesis aims to deepen the understanding of the involved Thermo-Hydro-Mechanical (THM) processes, in order to explain and manage co- and post-injection seismicity. First, we investigate the HM coupling and its effects on pressure response. Fluids injection exerts a force over the aquifer that causes deformation. This implies that Specific Storage, which reflects the capacity of permeable media to deform, cannot be treated as a single parameter, like in classical groundwater hydrology, because deformation also depends on aquifer geometry and on surrounding formations, which constrain displacements. We demonstrate the non-local nature of storage (i.e., its dependence on the poroelastic response over the whole aquifer) by means of analytical solutions to the transient pressure response to injection into one-dimensional and cylindrical finite aquifers, while acknowledging HM coupling. We find that the pressure response is faster and much greater than predicted with traditional solutions. Second, we consider non-isothermal injection and compare the effects of HM and TM couplings. We present analytical expressions for long-term hydraulic and thermal stresses and displacements for unidirectional and radial geometries. To obtain them, we assume steady-state fluid flow and develop an easy-to-use solution to the transient heat transport problem. The solution is then used to illustrate the poroelastic and thermoelastic response and, in particular, the sensitivity of stresses to the outer mechanical boundary conditions. Third, we perform coupled HM and THM simulations of cold water injection in a fault-intact rock system, which allows us to analyze mechanical stability changes during injection in the vicinity of the well. Simulation results show that temperature drop induces a significant perturbation of stresses in the intact rock near the injection well. This perturbation is likely to induce seismicity around critically oriented fractures. HM simulations show that fracture stability depends on the orientation of the faults and on the initial stress tensor. Results show that TM effects dominate and could induce seismicity, when the largest confining stress acts perpendicular to a fracture. Finally, we investigate the mechanisms that may induce seismicity after the end of fluid injection into a deep geothermal system (post-injection seismicity). Apart from the direct impact of fluid pressure increase, we acknowledge thermal effects due to cooling and stress redistribution caused by shear slip along favorably oriented fractures during injection. The effect of these three processes are analyzed both separately and superimposed. We find that post-injection seismicity may occur on unfavorably oriented faults that were originally stable. During injection, such faults become destabilized by thermal and shear slip stress changes, but remain static by the superposition of the stabilizing effect of pressure forces. However, these fractures become unstable and fail when the pressure forcing dissipates shortly after injection stops abruptly, which suggests that a slow reduction in injection rate may alleviate post-injection seismicity.
publishDate 2017
dc.date.none.fl_str_mv 2017
2017
2017
dc.type.none.fl_str_mv info:eu-repo/semantics/doctoralThesis
info:eu-repo/semantics/publishedVersion
format doctoralThesis
status_str publishedVersion
dc.identifier.none.fl_str_mv http://hdl.handle.net/10803/405890
https://dx.doi.org/10.5821/dissertation-2117-107946
url http://hdl.handle.net/10803/405890
https://dx.doi.org/10.5821/dissertation-2117-107946
dc.language.none.fl_str_mv Inglés
language_invalid_str_mv Inglés
dc.rights.none.fl_str_mv http://creativecommons.org/licenses/by-nc-sa/4.0/
info:eu-repo/semantics/openAccess
rights_invalid_str_mv http://creativecommons.org/licenses/by-nc-sa/4.0/
eu_rights_str_mv openAccess
dc.format.none.fl_str_mv 166 p.
application/pdf
application/pdf
dc.publisher.none.fl_str_mv Universitat Politècnica de Catalunya
publisher.none.fl_str_mv Universitat Politècnica de Catalunya
dc.source.none.fl_str_mv TDX (Tesis Doctorals en Xarxa)
reponame:TDR. Tesis Doctorales en Red
instname:CBUC, CESCA
instname_str CBUC, CESCA
reponame_str TDR. Tesis Doctorales en Red
collection TDR. Tesis Doctorales en Red
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spelling Induced seismicity in enhanced geothermal systems : assessment of thermo-hydro-mechanical effectsDe Simone, SilviaÀrees temàtiques de la UPC::Enginyeria civil55626Micro-seismicity, and especially felt seismicity, induced by Enhanced Geothermal Systems (EGS) operations is a matter of scientific interest, not only because of the related risks and concerns, but also because the correspondence between injection and seismic activity still remains unclear. The Thesis aims to deepen the understanding of the involved Thermo-Hydro-Mechanical (THM) processes, in order to explain and manage co- and post-injection seismicity. First, we investigate the HM coupling and its effects on pressure response. Fluids injection exerts a force over the aquifer that causes deformation. This implies that Specific Storage, which reflects the capacity of permeable media to deform, cannot be treated as a single parameter, like in classical groundwater hydrology, because deformation also depends on aquifer geometry and on surrounding formations, which constrain displacements. We demonstrate the non-local nature of storage (i.e., its dependence on the poroelastic response over the whole aquifer) by means of analytical solutions to the transient pressure response to injection into one-dimensional and cylindrical finite aquifers, while acknowledging HM coupling. We find that the pressure response is faster and much greater than predicted with traditional solutions. Second, we consider non-isothermal injection and compare the effects of HM and TM couplings. We present analytical expressions for long-term hydraulic and thermal stresses and displacements for unidirectional and radial geometries. To obtain them, we assume steady-state fluid flow and develop an easy-to-use solution to the transient heat transport problem. The solution is then used to illustrate the poroelastic and thermoelastic response and, in particular, the sensitivity of stresses to the outer mechanical boundary conditions. Third, we perform coupled HM and THM simulations of cold water injection in a fault-intact rock system, which allows us to analyze mechanical stability changes during injection in the vicinity of the well. Simulation results show that temperature drop induces a significant perturbation of stresses in the intact rock near the injection well. This perturbation is likely to induce seismicity around critically oriented fractures. HM simulations show that fracture stability depends on the orientation of the faults and on the initial stress tensor. Results show that TM effects dominate and could induce seismicity, when the largest confining stress acts perpendicular to a fracture. Finally, we investigate the mechanisms that may induce seismicity after the end of fluid injection into a deep geothermal system (post-injection seismicity). Apart from the direct impact of fluid pressure increase, we acknowledge thermal effects due to cooling and stress redistribution caused by shear slip along favorably oriented fractures during injection. The effect of these three processes are analyzed both separately and superimposed. We find that post-injection seismicity may occur on unfavorably oriented faults that were originally stable. During injection, such faults become destabilized by thermal and shear slip stress changes, but remain static by the superposition of the stabilizing effect of pressure forces. However, these fractures become unstable and fail when the pressure forcing dissipates shortly after injection stops abruptly, which suggests that a slow reduction in injection rate may alleviate post-injection seismicity.La micro-sismicitat induïda per operacions relacionades amb els Sistemes Geotèrmics Estimulats ha originat un gran interès científic, no només pel risc i la preocupació que comporta, sinó també perquè la relació entre la injecció de fluids i l'activitat sísmica no s'entén completament. Aquesta tesi pretén avançar en la comprensió dels processos hidro-termo-mecànics (THM) que causen aquesta sismicitat, per poder explicar-la i gestionar-la. En primer lloc, hem investigat l'acoblament hidro-mecànic (HM) i el seu efecte sobre les pressions. En Hidrologia Subterrània clàssica l'emmagatzematge especifico expressa la capacitat de l'aqüífer de deformar-se després d'una variació de pressió. Malgrat això, la sobrepressió generada per la injecció exerceix una força que deforma tot l'aqüífer, depenent de la seva geometria i de les formacions adjacents. Per això, l'emmagatzematge no es pot expressar amb un sol paràmetre, sinó que depèn de la resposta poro-elàstica de tot l'aqüífer, per la qual cosa diem que l'emmagatzematge específic és "no-local", cosa que vam mostrar mitjançant solucions analítiques de la resposta transitòria al problema HM de la injecció en aqüífers de dimensió finita, amb geometria tant unidimensional com cilíndrica. Seguidament, hem considerat una injecció no isoterma i comparat els efectes de l'acoblament hidro-mecànic (HM) i termo-mecànic (TM). Hem obtingut expressions analítiques per a les tensions i els desplaçaments induïts a llarg termini per la pertorbació hidràulica i tèrmica, en el cas de dominis unidireccional i radial. Per a això, hem considerat flux estacionari i desenvolupat una solució analítica senzilla per al transport de calor en règim transitori, la qual cosa ens ha permès calcular la resposta poro i termo-elàstica i en particular la sensibilitat de les tensions a les condicions mecàniques en el contorn exterior. A continuació, hem desenvolupat simulacions HM i THM acoblades de la injecció d'aigua freda en un sistema format per una falla embeguda en una roca intacta, a fi d'analitzar les variacions de l'estabilitat mecànica durant la injecció. Les simulacions HM mostren que l'estabilitat de les fractures depèn de la seva orientació i del tensor de tensions inicial. Concloem que la reducció de temperatura provoca prop del pou una forta pertorbació de les tensions, que pot induir sismes en fractures orientades críticament, especialment quan la tensió màxima actua perpendicularment a la fractura. Finalment, hem estudiat els mecanismes que poden induir sismes quan s'atura la injecció de fluids en sistemes geotèrmics profunds (sismicitat post-injecció). A més de l'efecte directe de l'augment de la pressió, hem considerat l'efecte tèrmic a causa del refredament i la redistribució de tensions generada pel moviment de cisalla que ocorre durant la injecció en fractures favorablement orientades. Aquests efectes s'han analitzat tant per separat com superposats. Dels resultats podem deduir que la sismicitat post-injecció pot ocórrer al llarg de fractures que eren inicialment estables i es desestabilitzen durant la injecció, a causa de les tensions tèrmiques i a les induïdes per la cisalla, però es mantenen estables gràcies a les forces de pressió. Posteriorment, aquestes fractures trenquen quan s'interromp la injecció, ja que les pressions es dissipen ràpidament. Això suggereix que la sismicitat post-injecció pot atenuar-se amb una reducció lenta del cabal d'injecció.DOCTORAT EN ENGINYERIA DEL TERRENY (Pla 2007)Universitat Politècnica de CatalunyaCarrera Ramírez, JesúsVilarrasa Riaño, VíctorUniversitat Politècnica de Catalunya. Departament d'Enginyeria Civil i Ambiental201720172017info:eu-repo/semantics/doctoralThesisinfo:eu-repo/semantics/publishedVersion166 p.application/pdfapplication/pdfhttp://hdl.handle.net/10803/405890https://dx.doi.org/10.5821/dissertation-2117-107946TDX (Tesis Doctorals en Xarxa)reponame:TDR. Tesis Doctorales en Redinstname:CBUC, CESCAInglésL'accés als continguts d'aquesta tesi queda condicionat a l'acceptació de les condicions d'ús establertes per la següent llicència Creative Commons: http://creativecommons.org/licenses/by-nc-sa/4.0/http://creativecommons.org/licenses/by-nc-sa/4.0/info:eu-repo/semantics/openAccessoai:www.tdx.cat:10803/4058902026-06-14T12:46:07Z
score 15.300724

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