Assessment and geological characterisation of the CO2CRC Otway Project CO2 storage demonstration site: From prefeasibility to injection

•Over 65,000 tonnes of CO2 has been stored safely in a depleted gas field.•Injectivity, capacity, and containment are essential for a storage site.•Relative permeability and reservoir heterogeneity effect CO2 migration.•Regional hydrodynamics and aquifer recharge can reduce capacity.•Targeted data acquisition and monitoring reduces uncertainty.

The CO2CRC Otway Project, located in south-eastern Australia, has demonstrated geological storage of CO2 in a depleted natural gas field. Prior to injection, a comprehensive site characterisation study established that the site should meet the requirements of safe and effective storage. In contrast to the conventional methods applied to characterising oil and gas reservoirs for production purposes, CO2 storage site assessments place greater emphasis on injectivity, capacity, and long-term containment. The site location was assessed in the context of accessibility for monitoring activities and impact on local communities and natural resources. Additional well-log data and cores were acquired from the gas field, in conjunction with the drilling of the CRC-1 injector well, in order to reduce the uncertainty surrounding the geological heterogeneity of the reservoir, capacity of the seal to retain CO2, fault seal geomechanics, and regional hydrodynamics. Specialised core analysis revealed that small scale sedimentary features, related to depositional environment impact reservoir quality, CO2 trapping and plume migration behaviour. Based on these effects, a depositional model was established to better understand storage potential away from well control. Finally, a nearby gas storage facility provided a valuable analogue for the project and added confidence that the CO2CRC Otway Project site would be suitable to inject, store and contain CO2 within the technological and economical limits of the project. Following the injection period, long term monitoring of the reservoir, as well as the overlying aquifers, soil, groundwater and the atmosphere above the site, have confirmed the storage concept is effective and that the CO2 is safely contained. As a result, the site characterisation methodology serves as an example for others contemplating CO2 storage into depleted gas fields.