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| Titel |
Coupled THM-statistical modeling of induced seismicity during deep geothermal exploitation |
| VerfasserIn |
Massimo Nespoli, Antonio Pio Rinaldi, Stefan Wiemer |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250112182
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| Publikation (Nr.) |
 EGU/EGU2015-12340.pdf |
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| Zusammenfassung |
| During deep geothermal exploitation, seismicity is unavoidably induced, posing potential
hazard for structures and concerns to the local community. Thus, understanding how to avoid
triggering of large earthquakes plays a crucial role in the success of underground
anthropogenic activities.
Recent works, combining physical consideration with stochastic elements, showed the
importance of developing tools for hazard and risk assessment that can operate in real-time
during reservoir stimulation, and which depend on the ability to efficiently model induced
seismicity.
Understanding the triggering mechanism is a fundamental step towards controlling the
seismicity generated by deep underground exploitation. Although seismicity is generally
controlled by fluid injection, it is not possible to rule out some other mechanisms such as
static stress transfers between neighbor asperities, or creep-mediated stress interactions along
the fault zone. In these conditions, the relationship between fluid pressure and induced
seismicity is much more complex. Moreover, while current modeling approaches focus
mostly on the active injection phase, the static stress transfer may become import at later
stage during the post-injection phase.
In order to address these effects, we here propose a novel modeling approach based on
coupling a Thermo-Hydro-Mechanical (THM) simulator with a statistical model. The THM
simulator provides the fluid flow and the poro-elastic deformation, and the permeability
may be enhanced by stress/strain changes. The transient pressure field is then used
to trigger events at so-called ‘seed points’ that are randomly distributed in space
and represent potential earthquake hypocenters. Assuming a fault orientation with
respect to the stress field and a Mohr–Coulomb failure criterion, we evaluate at
each time step, if a seed point is triggered by the pressure/stress change at the seed
location. In case of a triggered event, the magnitude of such event is randomly
assigned from a power-law distribution with a b value corresponding to the differential
stress at the triggered seed point. After reactivation, we calculate a stress drop and a
further permeability enhancement that are then fed back to the THM simulator. At
the same time step, the reactivation of seed point may also occur by static stress
transfer.
This strategy of modeling flow and seismicity in a decoupled manner has been shown to
ensure efficiency and flexibility of the model, and accounting for more detailed description of
stress and strain changes within the engineered reservoir provides a more comprehensive
representation of the triggering mechanics. |
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