relation: https://episodesplatform.eu/eprints/1684/
title: Degradation of the mechanical properties imaged by seismic tomography during an EGS creation at The Geysers (California) and geomechanical modeling
creator: Jeanne, Pierre
creator: Rutqvist, Jonny
creator: Hutchings, Lawrence
creator: Singh, Ankit
creator: Dobson, Patrick F.
creator: Walters, Mark
creator: Hartline, Craig
creator: Garcia, Julio
subject: Collective properties of seismicity
subject: Geysers
subject: Geothermal energy production
description: Using coupled thermal-hydro-mechanical (THM) modeling, we evaluated new seismic tomography  results associated with stimulation injection at an EGS demonstration project at the Northwest Geysers  geothermal steam field, California. We studied high resolution seismic tomography images built from  data recorded during three time periods: a period of two months prior to injection and during two consecutive  one month periods after injection started in October 2011. Our analysis shows that seismic  velocity decreases in areas of most intense induced microseismicity and this is also correlated with  the spatial distribution of calculated steam pressure changes. A detailed analysis showed that shear wave  velocity decreases with pressure in areas where pressure is sufficiently high to cause shear reactivation of  pre-existing fractures. The analysis also indicates that cooling in a liquid zone around the injection well  contributes to reduced shear wave velocity. A trend of reducing compressional wave velocity with fluid  pressure was also found, but at pressures much above the pressure required for shear reactivation. We  attribute the reduction in shear wave velocity to softening in the rock mass shear modulus associated  with shear dislocations and associated changes in fracture surface properties. Also, as the rock mass  become more fractured and more deformable this favors reservoir expansion caused by the pressure  increase, and so the fracture porosity increases leading to a decrease in bulk density, a decrease in Young  modulus and finally a decrease in Vp.
publisher: Elsevier
date: 2015
type: Article
type: NonPeerReviewed
identifier:   Jeanne, Pierre and Rutqvist, Jonny and Hutchings, Lawrence and Singh, Ankit and Dobson, Patrick F. and Walters, Mark and Hartline, Craig and Garcia, Julio  (2015) Degradation of the mechanical properties imaged by seismic tomography during an EGS creation at The Geysers (California) and geomechanical modeling.  Physics of the Earth and Planetary Interiors, 240.  pp. 82-94. DOI: https://doi.org/10.1016/j.pepi.2014.12.003 <https://doi.org/10.1016/j.pepi.2014.12.003>     
relation: http://doi.org/10.1016/j.pepi.2014.12.003
relation: doi:10.1016/j.pepi.2014.12.003