Induced seismicity within geological carbon sequestration projects: Maximum earthquake magnitude and leakage potential from undetected faults

Abstract

a b s t r a c tWith developing countries strongly relying on fossil fuels for energy generation, geological carbon sequestration (GCS) is seen as a candidate for large reductions in CO 2 emissions during the next several decades. GCS does, however, raise some safety concerns. Specifically, it has been associated with induced seismicity, as a result of pressure buildup arising from prolonged CO 2 injection in GCS projects. This seismicity is a delicate issue for two main reasons. First, over a short time scale, deformation of rock could release seismic energy, potentially affecting surface structures or simply alarming the population, with negative consequences for the social acceptance of this kind of projects. Second, over a longer time scale, activated faults may provide preferential paths for CO 2 leakage out of reservoirs. While known major faults intersecting target aquifers can be identified and avoided during site screening, the same might not be true for faults that are not resolvable by geophysical surveys. In this study, we use geological observations and seismological theories to estimate the maximum magnitude of a seismic event that could be generated by a fault of limited dimensions. We then compare our estimate with results of geomechanical simulations that consider faults with different hydrodynamic and geomechanical characteristics. The coupled simulations confirm the notion that the tendency of faults to be reactivated by the pressure buildup is linked with the in situ stress field and its orientation relative to the fault. Small, active (critically stressed) faults are capable of generating sufficiently large events that could be felt on the surface, although they may not be the source of large earthquakes. Active, relatively permeable faults may be detrimental concerning the effectiveness of a storage project, meaning that they could be preferential pathway for upward CO 2 leakage, although minor faults may not intersect both CO 2 reservoirs and shallower potable aquifers.Published by Elsevier Ltd.

Geologic carbon storage is unlikely to trigger large earthquakes and reactivate faults through which CO2could leak

“…Numerical simulations have shown that CO 2 injection in closed reservoirs without a proper control of overpressure, i.e., allowing overpressure to exceed the maximum sustainable injection pressure, has the potential of triggering earthquakes of up to magnitude 4.5 in critically stressed faults (86). However, the magnitude of the simulated induced earthquakes becomes smaller than 3 when considering more realistic stress fields for sedimentary formations, with shear displacements of up to 6 cm (86,87). These numerical studies highlight the importance of overpressure management for avoiding felt induced seismicity.…”

Modeling of fault activation and seismicity by injection directly into a fault zone associated with hydraulic fracturing of shale-gas reservoirs

“…The adopted modeling approach has also been extensively applied for modeling fault activation associated with underground CO 2 injection (e.g. Cappa and Rutqvist, 2012;Mazzoldi et al, 2012;.…”

An overview of TOUGH-based geomechanics models

“…2011), TOUGH-FLAC was expanded to applications, including geomechanical aspects of CO 2 sequestration and fault activation, geomechanical effects in gas production from hydrate bearing sediments, and geothermal energy production. Since 2011, TOUGH-FLAC applications have been further broadened along with an increasing number of users, including continued modeling of geomechanical aspects of CO 2 sequestration (Cappa and Mazzoldi et al, 2012;Rinaldi and Rutqvist, 2013;Jeanne et al, 2014a;Konstantinovskaya et al, 2014;Rinaldi et al, 2014aRinaldi et al, , b, 2015aFigueiredo et al, 2015), nuclear waste disposal , enhanced geothermal systems (Jeanne et al, 2014b(Jeanne et al, -d, 2015aRutqvist et al, 2015a;Rinaldi et al, 2015b), underground gas storage and compressed air energy storage 2015), and gas production from hydrate bearing formations ).…”