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Analysis of fluid injection‐induced fault reactivation and seismic slip in geothermal reservoirs
Author(s) -
Gan Quan,
Elsworth Derek
Publication year - 2014
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2013jb010679
Subject(s) - geothermal gradient , permeability (electromagnetism) , geology , slip (aerodynamics) , thermal , heat transfer , pore water pressure , geotechnical engineering , mechanics , geophysics , thermodynamics , chemistry , biochemistry , physics , membrane
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 m 2 ), 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.