Evaluation of seismic monitoring methods from the Aquistore CO2 storage site in Canada

The Aquistore CO₂ storage site lies within the Williston Basin in southeastern Saskatchewan, Canada. The storage reservoir is a 200 m thick saline clastic formation at a depth of 3150 m. 600,000 tonnes of CO₂ have been injected at the site since 2015.

 A variety of geophysical monitoring methods have been employed at the Aquistore site. The primary tools for tracking the evolution of the CO₂ plume over time are time-lapse (4D) seismic acquired with a permanent 2D array of shallow buried geophones and VSPs using a well-based distributed acoustic sensing (DAS) cable. 3D surface seismic and VSPs have been acquired when injected CO₂ amounts were 0, 36, 102, 141, and 272 ktonnes, respectively [1,2], with the most recent surveys conducted in November, 2023 when 566,000 tonnes of  CO₂ were injected. The 4D seismic data image a primary CO₂  plume within a ~10 m thick high-permeability zone. The plume has continued to expand in sequential 4D images with an interpreted structural flexure/basement fault significantly affecting the flow of CO₂ away from the injection well.

Other geophysical monitoring methods that have been utilized at the Aquistore site include crosswell seismic tomography and DAS surface seismic acquisition using novel fibre cable configurations. Time-lapse crosswell seismic reflection and velocity images have been obtained using full waveform inversion and VSP-reflection imaging techniques. The observed CO₂-related velocity changes are particularly important as they provide a means of calibrating the surface seismic data. Following an initial test of fibre optic cable configurations for surface seismic acquisition [3], a large-scale field test of shallow vertical fibre loops was conducted in November-2023 to record a full 3D dynamite seismic survey at the Aquistore site. A total of 8000 m of tactical optical fibre cable was buried at 80 cm depth along 6 receiver lines of the existing permanent geophone array at the site with the fibre forming a continuous run with 3 m vertical loops installed adjacent to the geophones along the line for a total of 95 spatially coincident fibre loops and geophones. Results from this survey demonstrate comparable imaging results for the data from the geophones and fibre loops.

References

[1] Roach, L.A.N., and White, D.J., 2018. Evolution of a deep CO2 plume from time-lapse seismic imaging at the Aquistore Storage Site, Saskatchewan, Canada, International Journal of Greenhouse Gas Control, 74, 79-86.

[2] Movahedzadeh, Z., Rangriz Shokri, A., Chalaturnyk, R., Nickel, E., and Sacuta, N., 2021. Measurement, monitoring, verification and modelling at the Aquistore CO₂ storage site, First Break, 39(2), 69-75.

[3] White, D.J., Bellefleur, G., Dodds, K., and Movahedzadeh, Z., 2022. Toward Improved DAS Sensitivity for Surface-Based Reflection Seismics: Configuration Tests at the Aquistore CO₂ Storage Site, Geophysics, 87(2), 1-14.