TY  - JOUR
ID  - epos1684
UR  - http://doi.org/10.1016/j.pepi.2014.12.003
A1  - Jeanne, Pierre
A1  - Rutqvist, Jonny
A1  - Hutchings, Lawrence
A1  - Singh, Ankit
A1  - Dobson, Patrick F.
A1  - Walters, Mark
A1  - Hartline, Craig
A1  - Garcia, Julio
Y1  - 2015///
N2  - 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.
PB  - Elsevier
JF  - Physics of the Earth and Planetary Interiors
VL  - 240
KW  - Enhanced Geothermal System
Microseismic events
Geomechanical simulation
Seismic tomography
Vp/Vs
SN  - 0031-9201
TI  - Degradation of the mechanical properties imaged by seismic tomography during an EGS creation at The Geysers (California) and geomechanical modeling
SP  - 82
AV  - none
EP  - 94
ER  -