Geologic carbon storage is unlikely to trigger large earthquakes and reactivate faults through which CO₂ could leak
2015
Vilarrasa, Victor | Carrera Ramírez, Jesús
Zoback and Gorelick [(2012) Proc Natl Acad Sci USA 109(26):10164–10168] have claimed that geologic carbon storage in deep saline formations is very likely to trigger large induced seismicity, which may damage the caprock and ruin the objective of keeping CO ₂ stored deep underground. We argue that felt induced earthquakes due to geologic CO ₂ storage are unlikely because ( i ) sedimentary formations, which are softer than the crystalline basement, are rarely critically stressed; ( ii ) the least stable situation occurs at the beginning of injection, which makes it easy to control; ( iii ) CO ₂ dissolution into brine may help in reducing overpressure; and ( iv ) CO ₂ will not flow across the caprock because of capillarity, but brine will, which will reduce overpressure further. The latter two mechanisms ensure that overpressures caused by CO ₂ injection will dissipate in a moderate time after injection stops, hindering the occurrence of postinjection induced seismicity. Furthermore, even if microseismicity were induced, CO ₂ leakage through fault reactivation would be unlikely because the high clay content of caprocks ensures a reduced permeability and increased entry pressure along the localized deformation zone. For these reasons, we contend that properly sited and managed geologic carbon storage in deep saline formations remains a safe option to mitigate anthropogenic climate change.
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