Field tests of geological storage of CO ₂ at the Otway International Test Centre, Australia: trapping and monitoring the migrating plumes

Abstract

The capture and geological storage of CO 2 is essential for net zero. Large volumes of secure subsurface storage will be required, much in unexplored saline aquifers. At the Otway International Test Centre we have executed a series of storage tests, including geophysical surveys, geochemical and petrophysical characterisation, drilling and instrumenting six deep wells and conducting two intensively monitored injections each of 15 Kt CO 2 . We summarise the execution and outcomes to draw out the implications for larger-scale storage and for migration trapping of CO 2 plumes. Immobilisation of most of the plume is essential for long-term safety. Suitable saline aquifers should have sealing caprocks but need not have structural traps. Buoyant CO 2 could move kilometres beneath the seal, with immobilisation occurring by capillary forces and dissolution. Predicting and monitoring plume behaviour with practical methods integrated with risk management will be necessary. We characterised and monitored migration trapping, demonstrated plume immobilisation, and tested monitoring methods tailored to large saline aquifers. We developed pressure tomography and continuous seismic monitoring; these provide less detailed information than conventional methods but can be targeted at risks. Passive methods, such as the seismic response to earthquakes, can also act as sentinels for specific events. These methods can bridge the "monitoring gap" between detailed but infrequent methods and more frequent but simpler methods and the results will enable better trade-offs between cost, complexity and risk for a technology crucial for controlling CO 2 levels in the atmosphere. Supplementary material: https://doi.org/10.6084/m9.figshare.c.7148197