Title: Seismic and aseismic deformations and impact on reservoir permeability: The case of EGS stimulation at The Geysers, California, USA

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 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. 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 fracturesmore » 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.« less

Authors:

Jeanne, Pierre ^[1]; Rutqvist, Jonny ^[1]; Rinaldi, Antonio Pio ^[2]; Dobson, Patrick F. ^[1]; Walters, Mark ^[3]; Hartline, Craig ^[3]; Garcia, Julio ^[3]

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+ Show Author Affiliations

1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
2. Swiss Federal Institute of Technology, ETHZ, Zurich (Switzerland)
3. Calpine Corp., Middletown, CA (United States)

Publication Date:

Tue Oct 27 00:00:00 EDT 2015

Research Org.:

Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Geothermal Technologies Office

OSTI Identifier:

1410322

Grant/Contract Number:  

AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Geophysical Research. Solid Earth

Additional Journal Information:

Journal Volume: 120; Journal Issue: 11; Journal ID: ISSN 2169-9313

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; enhanced geothermal system; microseismicity; thermo-hydro-mechanical simulation; aseismic deformations; permeability gain