Semi-continuous Electric Resistivity Tomography monitoring of a CO2 injection pilot site, CaMI Field Research Station, Newell County, Alberta, Canada

Abstract:

The Field Research Station of the Containment and Monitoring Institute (CaMI.FRS) has been developed jointly by CMC Research Institutes Inc. and the University of Calgary to develop and assess monitoring technologies for secure geologic storage of CO₂. At the CaMI.FRS, a small amount of CO₂ (currently ~1.25 tonnes per month) is being injected at shallow depth (300 m) into sandstones of the Basal Belly River Formation. Baseline conditions and injection cycles are being monitored using a wide range of geophysical methods. We focus in this paper on the Electric Resistivity Tomography (ERT) using a 16-electrode downhole array in an observation well that is 20 m from the CO₂ injection well, and 128 electrodes permanently installed at 10 m intervals along a 1.1 km surface trench that is centred on the injection well. Electrical methods have the advantage of being highly sensitive to changes in CO₂ saturation, making it a good candidate for the monitoring CO2 saturation levels at the CaMI.FRS site. Since August 2019, we recorded daily surveys using different electrode configurations (Wenner, dipole-dipole and Schlumberger using borehole-borehole, borehole-surface and surface-surface configurations). The resistivity data show an increase in the resistivity with time, induced by the CO₂ injection (Figure 1). Between August 2019 and July 2020, 10 tonnes of CO₂ were injected, and we observe an increase of +4.5% in the average resistivity values across the reservoir interval. Resistivity data are being inverted to get an estimate of the CO₂ saturation.