eprintid: 1830 rev_number: 13 eprint_status: archive userid: 6 dir: disk0/00/00/18/30 datestamp: 2017-03-02 10:24:47 lastmod: 2017-05-16 12:22:20 status_changed: 2017-03-02 10:24:47 type: article metadata_visibility: show creators_name: Jeanne, Pierre creators_name: Rutqvist, Jonny creators_name: Rinaldi, Antonio Pio creators_name: Dobson, Patrick F. creators_name: Walters, Mark creators_name: Hartline, Craig creators_name: Garcia, Julio corp_creators: Earth Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA corp_creators: Earth Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA corp_creators: Swiss Seismological Service, Swiss Federal Institute of Technology, ETHZ, Zürich, Switzerland corp_creators: Earth Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA corp_creators: Calpine Corporation, Middletown, California, USA corp_creators: Calpine Corporation, Middletown, California, USA corp_creators: Calpine Corporation, Middletown, California, USA title: Seismic and aseismic deformations and impact on reservoir permeability: The case of EGS stimulation at The Geysers, California, USA subjects: MP4 subjects: RU1_1 subjects: SG divisions: SHEER-5 full_text_status: none abstract: In this paper, we use the Seismicity-Based Reservoir Characterization approach to study the spatiotemporal dynamics of an injection-induced microseismic cloud, monitored during the stimulation of an enhanced geothermal system, and associated with the Northwest Geysers Enhanced Geothermal System (EGS) Demonstration project (California). We identified the development of a seismically quiet domain around the injection well surrounded by a seismically active domain. Then we compare these observations with the results of 3-D Thermo-Hydro-Mechanical simulations of the EGS, which accounts for changes in permeability as a function of the effective normal stress and the plastic strain. The results of our modeling show that (1) the aseismic domain is caused by both the presence of the injected cold water and by thermal processes. These thermal processes cause a cooling-stress reduction, which prevent shear reactivation and favors fracture opening by reducing effective normal stress and locally increasing the permeability. This process is accompanied by aseismic plastic shear strain. (2) In the seismic domain, microseismicity is caused by the reactivation of the preexisting fractures, resulting from an increase in injection-induced pore pressure. Our modeling indicates that in this domain, permeability evolves according to the effective normal stress acting on the shear zones, whereas shearing of preexisting fractures may have a low impact on permeability. We attribute this lack of permeability gain to the fact that the initial permeabilities of these preexisting fractures are already high (up to 2 orders of magnitude higher than the host rock) and may already be fully dilated by past tectonic straining. date: 2015-11 date_type: published publication: Journal of Geophysical Research: Solid Earth volume: 120 number: 11 publisher: John Wiley & Sons pagerange: 7863-7882 id_number: doi:10.1002/2015JB012142 issn: 2169-9313 official_url: http://doi.org/10.1002/2015JB012142 access_IS-EPOS: limited owner: Publisher citation: Jeanne, Pierre and Rutqvist, Jonny and Rinaldi, Antonio Pio and Dobson, Patrick F. and Walters, Mark and Hartline, Craig and Garcia, Julio (2015) Seismic and aseismic deformations and impact on reservoir permeability: The case of EGS stimulation at The Geysers, California, USA. Journal of Geophysical Research: Solid Earth, 120 (11). pp. 7863-7882. DOI: https://doi.org/10.1002/2015JB012142