TY - JOUR
T1 - Analysis of fluid injection‐induced fault reactivation and seismic slip in geothermal reservoirs
AU - Gan, Quan
AU - Elsworth, Derek
N1 - This work is the result of partial support from the U.S. Department of Energy under project DOE-DE-EE0002761. This support is gratefully acknowledged.
PY - 2014/4
Y1 - 2014/4
N2 - We explore the issue of fault reactivation induced in enhanced geothermal systems by fluid injection. Specifically, we investigate the role of late stage activation by thermal drawdown. A Thermal-Hydrological-Mechanical simulator incorporating a ubiquitous joint constitutive model is used to systematically simulate the seismic slip of an embedded critically stressed strike-slip fault. We examine the effects of both pore pressure perturbation and thermal shrinkage stress on the magnitude of the resulting events and timing. We analyze the sensitivity of event magnitude and timing to changes in the permeability of the fault and fractured host, fracture spacing, injection temperature, and fault stress obliquity. From this we determine that (1) the fault permeability does not affect the timing of the events nor their size, since fluid transmission and cooling rate are controlled by the permeability of the host formation. (2) When the fractured medium permeability is reduced (from 10−13 to 10−16 m2), the timing of the event is proportionately delayed (by a corresponding 3 orders of magnitude). (3) Injection temperature only influences the magnitude but not the timing of the secondary thermal event. The larger the temperature differences between that of the injected fluid and the ambient rock, the larger the magnitude of the secondary slip event. (4) For equivalent permeabilities, changing the fracture spacing (10 m-50 m-100 m) primarily influences the rate of heat energy transfer and thermal drawdown within the reservoir. Smaller spacing between fractures results in more rapid thermal recovery but does not significantly influence the timing of the secondary thermal rupture.
AB - We explore the issue of fault reactivation induced in enhanced geothermal systems by fluid injection. Specifically, we investigate the role of late stage activation by thermal drawdown. A Thermal-Hydrological-Mechanical simulator incorporating a ubiquitous joint constitutive model is used to systematically simulate the seismic slip of an embedded critically stressed strike-slip fault. We examine the effects of both pore pressure perturbation and thermal shrinkage stress on the magnitude of the resulting events and timing. We analyze the sensitivity of event magnitude and timing to changes in the permeability of the fault and fractured host, fracture spacing, injection temperature, and fault stress obliquity. From this we determine that (1) the fault permeability does not affect the timing of the events nor their size, since fluid transmission and cooling rate are controlled by the permeability of the host formation. (2) When the fractured medium permeability is reduced (from 10−13 to 10−16 m2), the timing of the event is proportionately delayed (by a corresponding 3 orders of magnitude). (3) Injection temperature only influences the magnitude but not the timing of the secondary thermal event. The larger the temperature differences between that of the injected fluid and the ambient rock, the larger the magnitude of the secondary slip event. (4) For equivalent permeabilities, changing the fracture spacing (10 m-50 m-100 m) primarily influences the rate of heat energy transfer and thermal drawdown within the reservoir. Smaller spacing between fractures results in more rapid thermal recovery but does not significantly influence the timing of the secondary thermal rupture.
U2 - 10.1002/2013JB010679
DO - 10.1002/2013JB010679
M3 - Article
VL - 119
SP - 3340
EP - 3353
JO - Journal of Geophysical Research: Solid Earth
JF - Journal of Geophysical Research: Solid Earth
SN - 2169-9313
IS - 4
ER -