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 that can be used to reduce man-made CO2 emissions. This is achieved by separating and capturing CO2 from emission sources, then injecting and storing it in the subsurface. However, CCS requires the secure retention of CO2 in geological formations over thousands of years. Several geochemical and geophysical (such as time-lapse seismic) techniques allow the monitoring of the regional distribution of CO2 in the gas storage, seal integrity and the pressure evolution in response to the injection and, therefore, can be used to verify storage conformance and are valuable tools for integrity monitoring.
A seismic cross-hole field experiment to monitor a CO2 injection was carried out in September 2021 by Geotomographie in the framework of the EU funded DIGIMON project at the SINTEF CO2 field lab in Svelvik, Norway. The seismic experiment was supposed to monitor the propagation of CO2 (gas) during using high-resolution P-wave tomography. A comparison of two tomographic images between a baseline data set and data acquired at later injection stage show the migration of CO2.
Storing nuclear waste is a world-wide problem. A few years ago, the German government decided to search for a permanent nuclear storage location. The waste is divided into categories depending on radiation and origin. A geologically stable repository and leak-proof waste containers are required. Storage depths should be more than 300 m. In Germany claystone, salt and crystalline rocks have been identified to be potentially capable for waste storage.
Seismic tomography can be used to map the structures between boreholes at high resolution. The example shows a tomogram measured a few hundred meters below ground and at a distance of more than 100 m. This tomogram should demonstrate the capability of the method to map geological structures and to contribute to a wider knowledge base for planning repositories.
Crosshole seismic tomogram