Assessing the potential of passive seismic monitoring to detect a CO2 leak from the aquistore storage site

Summary This paper investigates the potential for passive seismic monitoring (PSM) to detect a CO2 leak for two possible scenarios, where a leak is seismic or aseismic. The Aquistore research project in Saskatchewan, Canada provides a suitable site to investigate this because the site is comprehensively monitored. To understand whether induced seismicity would occur following a hypothetical leak, we conduct modelling of fluid flow through a vertical fault. In the event of an aseismic leak, we assess the potential for ambient noise interferometry (ANI) and a tomographic inversion for Rayleigh wave group-velocity maps to provide a suitable CO2 leakage detection tool. A time-lapse ambient noise tomography survey of a CO2 storage site is possible for the first time because data is available preceding and following injection start-up. The fluid-flow modelling shows that a CO2 leak through a vertical fault would result in induced seismic events at depths <500 m. Predicted changes in seismic velocities with CO2 saturation at Aquistore are too small to resolve with the current precision of surface-wave velocity models. However, ANI may be useful to provide a cost-effective early warning system for leakage if uncertainties are reduced.