South West Hub CCS Project: Evolution of Storage Site Characterization through Targeted Research and its Impact on Uncertainty Reduction

The 2015 COP 21 meeting in Paris highlighted the urgency for more research into mitigation methods for greenhouse gases, yet there remain a small global portfolio of active investigations into large-scale geological storage of CO₂. The South West Carbon Capture and Storage Hub in Western Australia is one of these projects, and is a greenfield investigation with little pre-existing subsurface data available to perform the required geological characterisation; thus acquiring geoscience data for the site has been a concentrated effort during the past several years. Research into the South West Hub project has focussed on acquiring and interpreting appropriate data to progressively refine the storage concept, and better understand and reduce uncertainties associated with the geological character of the storage site. The initial consideration for the South West Hub was to inject CO₂ into Triassic sandstones in the southern Perth Basin at 2 to 3 km depth near a structural feature known as the Harvey Ridge. In this concept containment of the CO₂ was mainly through residual trapping within these deposits. Research is now focussing on the recognition of potential for a multi-containment system being present in the Triassic Lesueur Formation that includes the lower Wonnerup Member and upper Yalgorup Member. Injection would be into sandstones of the Wonnerup in which residual trapping can occur; the overlying Yalgorup potentially represents a series of strata that may impede upward migration of fluids, and comprises a succession of heterogeneous strata including a series of bands or pods of fine-grained and low permeability palaeosols which are up to 200 m thick beneath a sequence of interbedded clay-rich beds. 3D seismic data obtained in 2014 have provided more clarity around subsurface structures, fault locations, orientations and insight into regional stress fields. Core and log data from three wells drilled in 2015 into the Yalgorup are helping to establish the depositional nature, stratigraphic correlation and regional continuity of the possible baffle units within this member. Core-based work on pore-scale processes is developing knowledge about the impacts of CO₂ injected into Wonnerup sandstones and how it may be distributed and retained for long-term storage. Together the seismic and well data are being integrated toward more detailed static and dynamic models for simulations of trapping potential and long-term behaviour of injected CO₂. Monitoring methods are being examined and field tested to establish environmental baselines and to ensure the ability to validate models and for public and regulatory assurance. Ongoing phases of research will continue to focus on reducing technical uncertainty at the South West Hub storage site. Addressing several outstanding questions about injectivity and containment at the site are driving additional research involving in situ well tests.