CS-D: an In-Situ Experiment to Monitor Fault Sealing in Caprock for CO2 Geological Storage

Abstract:

Assessing the potential for leakage through faults plays a key role for the long-term containment of CO₂. Faults through a caprock represent one of the possible pathways for CO₂ to escape deep storage reservoir. Thus, the presence of faults in caprocks will strongly affect the site characterization process, and consequently the monitoring, verification, and risk management plans.

Here we present the results of an experiment performed at the Mont Terri underground rock laboratory (NW Switzerland) located in a clay formation that is a good analogue of common caprock for CO₂ storage. The experiment goal was to improve our understanding on the main mechanisms controlling the migration of CO₂ through a fault, and the impact of a prolonged injection on the transmissivity in the fault. To this end, we injected for more than one year CO₂-saturated saline water in the top of a 3 m thick fault in the clay. The mobility of the CO₂ within the fault was studied at decameter scale, by using a comprehensive monitoring system. The experiment offered a unique opportunity to develop improved, and more integrated monitoring technologies. In particular, a multi-component monitoring network integrates strain monitoring, micro-seismicity and active seismic monitoring, electrical resistivity monitoring, and in situ dissolved gas monitoring via a portable mass spectrometer.

The in situ monitoring was complemented by lab tests on geochemistry of fluid samples and geomechanical tests on rock samples. The monitoring program will be continued well after the end of injection in order to allow for studying not only the short-term poro-visco-elastic response, but also the geochemical and mineralogical changes within the damaged zone. This experiment will help improving the methods for monitoring and imaging fluid flow.