Monitoring Co2 Injection into Basaltic Reservoir Formations at the HellisheiÐi Geothermal Site in Iceland: Laboratory Experiments

In the ACT Consortium funded project SUCCEED, researchers study the potential for monitoring the process of (re-)injecting produced and captured CO2 into the Hellisheiði geothermal field for the aid of enhancing geothermal deployment as well as permanently storing CO2 through mineralization. The Hellisheiði site provides an excellent opportunity for demonstrating an innovative seismic monitoring technique. Prior to conducting an active-source monitoring survey, we perform acoustic transmission measurements, on Hellisheiði rock samples, at field-representative stress conditions to obtain the seismic-response characteristics of all present formations. Subsequently, we use the acquired velocity data as an input for simulating 2D seismic surveys using a subsurface model representing the Hellisheiði site. Results show that the impact of increasing depth, i.e., stress, on seismic velocities is most apparent for the porous basalt layers due to their relatively large portion of open pore space, allowing for substantial compaction, increasing their bulk density and thus velocity. The poorly-consolidated hyaloclastites reveal a negligible effect of increasing depth on their velocity as the material already reached its maximum compaction at low stresses, thus at shallow depths. Comparison of synthetic and field geophone data reveal that the velocity profiles have to be updated for the shallow depths in the model.