Faults can be potential leakage pathways for geological storage projects. The Otway Shallow Fault Experiment was conducted at the Otway International Test Centre in April 2024 after 8 years of planning, detailed characterisation and modelling. Specifically designed to achieve leakage, this world first experiment tracked CO₂ migration vertically up the fault and its release through the soil into the atmosphere. The experiment involved injecting 16 tonnes of CO₂ into the Port Campbell Limestone aquifer over an 8 day period at approximately 70 m depth, adjacent the predominantly strike slip Brumbys Fault. The experiment was a success, with the observed CO₂ migration behaviour matching the predicted modelled behaviour. 

 

Extensive preparation went into characterising the site prior the experiment including a ultra high resolution 3D seismic survey, LIDAR survey, 4 wells equipped with fibre optics, coring through the fault zone, wireline logs, geochemical analysis, and an extensive multi-year groundwater level monitoring program. These results were used to prepare a detailed geological model of the site, which enabled dynamic modelling and simulations of CO₂ migration behaviour under different injection scenarios. The groundwater monitoring provided insight into the nature of the aquifer, the permeability of the fault, and permeability of the overlying clay layer at the site. Vertical 2.5D sand tank analog models were used to validate the simulation results in terms of fluid migration pathways, including CO₂ migration time. 

 

Monitoring the CO₂ migration behaviour during the experiment using reverse 4D VSP revealed that the CO₂ migrated vertically up the fault zone as expected. Soil flux monitoring determined that the CO₂ reached the surface within 30 hours. Adjusted for the actual injection rate and pressure during the experiment, CMG GEM modelling predicted the CO₂ would reach the surface clay layer in 40 hours. This experiment provides confidence that current fault modelling approaches are effective and these are the same techniques used assess security of large scale storage of CO₂ against mapped faults at depth.