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| Titel |
Induced seismicity and CO2 leakage through fault zones during large-scale underground injection in a multilayered sedimentary system |
| VerfasserIn |
Antonio Pio Rinaldi, Jonny Rutqvist, Pierre Jeanne, Frédéric Cappa, Yves Guglielmi |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250088984
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| Publikation (Nr.) |
 EGU/EGU2014-3164.pdf |
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| Zusammenfassung |
| Overpressure caused by the direct injection of CO2 into a deep sedimentary system may
produce changes in the state of stress, as well as, have an impact on the sealing capabilities of
the targeted system. The importance of geomechanics including the potential for reactivating
faults associated with large-scale geologic carbon sequestration operations has recently
become more widely recognized. However, not withstanding the potential for triggering
notable (felt) seismic events, the potential for buoyancy-driven CO2 to reach potable
groundwater and the ground surface is more important from safety and storage-efficiency
perspectives.
In this context, this work extends previous studies on the geomechanical modeling of fault
responses during underground carbon dioxide injection, focusing on both short- and
long-term integrity of the sealing caprock, and hence of potential leakage of either brine or
CO2 to shallow groundwater aquifers during active injection.
The first part of this work aims to study the fault responses during underground carbon
dioxide injection, focusing on the short-term (5 years) integrity of the CO2 repository, and
hence on the potential leakage of CO2 to shallow groundwater aquifers. Increased pore
pressure can alter the stress distribution on a fault/fracture zone, which may produce
changes in the permeability related to the elastic and/or plastic strain (or stress)
during single (or multiple) shear ruptures. We account for stress/strain-dependent
permeability and study the leakage through the fault zone as its permeability changes
along with strain and stress variations. We analyze several scenarios related to the
injected amount of CO2 (and hence related to potential overpressure) involving
both involving minor and major faults, and analyze the profile risks of leakage for
different stress/strain permeability coupling functions, as well as increasing the
complexity of the system in terms of hydromechanical heterogeneities. We conclude that
whereas it is very difficult to predict how much fault permeability could change upon
reactivation, this process can have a significant impact on the leakage rate. Moreover, our
analysis shows that induced seismicity associated with fault reactivation may not
necessarily open up a new flow path for leakage. Results show a poor correlation
between magnitude and amount of fluid leakage, meaning that a single event is
generally not enough to substantially change the permeability along the entire fault
length.
In the second part of this work we address the three following questions: (1) is there
a link between fault-zone architecture and fault reactivation by CO2 injection?
(2) what is the impact of the fault architecture on the induced seismicity and on
CO2 leakage? and (3) how do caprock and reservoir thickness impact the results?
We analyze the hydromechanical behavior of a fault zone represented either by:
(i) a continuous damage zone, or by a discontinuous damage zone caused by (ii)
variations in lithology of the different layers (shale caprock and limestone aquifers), and
also by (iii) the initial properties of the sedimentary layers within the injection
reservoir itself. We use the model to estimate the moment magnitude associated
with a sudden fault slip event as well as the amount of CO2 migrating from the
injection aquifer and upwards across the primary caprock located just above the
injection aquifer after a long-term post-injection period. We recognize that such
migration out of the injection aquifer may not formally constitute CO2 leakage
up into potable shallow aquifers, if for example there is leak-off into intervening
aquifers or multiple overlying low permeability formations that prevent further upward
migration of the CO2. Finally, results show that a thin caprock or aquifer allows smaller
events, but a much higher percentage of leakage in the upper aquifer. The elevate
amount of leakage reduces drastically by assuming a multi-caprock, multi-aquifer
system. |
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