Sensitivity of controlled-source electromagnetic method for monitoring of CO2 storage at the Aquistore sequestration site, Canada: A modelling study

We investigate the sensitivity of surface controlled-source electromagnetic (CSEM) monitoring for CO 2 storage in the Aquistore project (Saskatchewan, Canada), where injection occurs at 3200 m depth. The sensitivity of frequency-domain electric-field responses to CO 2 plume evolution was evaluated using six forward modelling scenarios: three assuming homogeneous 90% post-injection CO 2 saturation, and three representing heterogeneous CO 2 saturation reflecting more realistic resistivity distributions. Detectability is assessed using the scattered electric fields, proportional changes in electric-field magnitudes (anomalous fields), and time-lapse phase variations. For a four-layered model, galvanic connection of the bipole source to a steel-cased injection well enhances scattered electric fields by more than two orders of magnitude at low frequencies. For in-line configurations, sensitivity to plume change is greatest between 0.1–1 Hz, at offsets of 5–10 km. For a realistic 18-layered resistivity structure, the present 10 m-thick CO 2 plume produces responses below typical detection thresholds but defines minimum requirements for a viable system: post-processing noise levels of 10⁻¹⁵ V/(A.m²), anomalous field sensitivity of ∼0.5%, and time-lapse phase resolution of ∼0.3°. We demonstrate CSEM response depends weakly on plume depth and radius but strongly on thickness, with anomalous magnitude and phase increasing almost proportionally. An 80 m-thick plume from future commercial-scale injection would yield anomalous magnitude changes >5% and phase changes >1.5°. Leakage into shallower carbonate units produces smaller responses than formation of the original plume, with changes dominated by effects of loss from the reservoir. The study also examines areal electric field distribution and effects of transverse anisotropy.