Monitoring Velocity Changes of P-, SH- and SV-waves during a CO2 Injection at the Svelvik Test-Site

In recent years, global concerns about greenhouse gas emissions have stimulated considerable interest in carbon capture and storage (CCS) as a climate change mitigation option. A significant issue for storage security is the geomechanical response of the reservoir. For instance, there are injection-induced stress, strain, deformations, and potential microseismic events resulting from changes in reservoir pressure and temperature. Unwanted unelastic mechanical changes might reduce sequestration efficiency and cause concerns in the local community. Accurate time-lapse surveys can be used to image changes in seismic velocity induced by geomechanical deformation. Within the ACT-funded DigiMon project, a seismic field test was planned and carried out in September 2021 at the CO2 field lab in Svelvik near Drammen in Norway. At the Svelvik test-site, an injection well and four observation wells with a depth of 100 m are installed. The observation wells are positioned at the corners of a rhombus around the injection well. The experiment was designed to monitor the propagation of CO2 during the injection using high-resolution P-wave seismic tomography with conventional receivers (hydrophones) and the installed DAS (Distributed Acoustic Sensing) cables. Furthermore, S-wave sources were used to generate SH- and SV-waves during different stages of injection.