Identifying potential basin areas for future Geological Storage of CO2 (GSC) exploration is essential to support Australia’s transition to a net zero emissions energy future. Geoscience Australia’s AFER Project has completed a play-based assessment of the GSC potential in the Pedirka and western Eromanga basins using regionally extensive aquifers containing saline to slightly brackish formation waters. There are currently no significant anthropogenic CO2 sources or associated storage projects in the assessment area. Understanding the area’s GSC potential does, however, assist in providing options for addressing CCS requirements in the central Australian region, including any future opportunities to remove anthropogenic CO2 using Direct Air Capture and Storage technologies.
The AFER Project’s assessments are underpinned by new geological insights into the basins and a supporting upscaled 3D geological model. A play-based common risk segment mapping approach has been applied to five potential storage (play) intervals to delineate basin areas with relatively high prospectivity based on four geological risk elements: injectivity, storage effectiveness, containment, and structural complexity. Results from this qualitative component of the assessment highlights a potentially prospective area for future GSC exploration extending across the Northern Territory, South Australia and Queensland. The most prospective interval on a geological probability of success basis is the Namur-Murta play interval.
Results from the qualitative GSC assessment have been used as a screening tool to delineate areas for quantitative modelling of the range of Estimated Ultimate Storage (EUS) volumes using deterministic and probabilistic methodologies. EUS volumes have been estimated in two model areas representing geological end members in storage interval heterogeneity and potentially prospective areas outside of the extents of current national parks. The EUS potential is high (10’s of gigatonnes) in the two model areas using both deterministic and probabilistic workflows, as expected for a regional assessment using very large pore volumes. Applying a geological probability of success based on injectivity and structural and stratigraphic containment reduces the volumes in the two model areas to a risked best estimate EUS of 13 Gt in the eastern area and a risked best estimate EUS of 2 Gt in the western area. Results from the quantitative assessment suggest that both model areas can support multiple industrial-scale CCS projects injecting 50 Mt CO2 over a 20-year period. However, heterogeneous reservoirs that extend over the eastern assessment area are likely to have greater storage efficiencies and an associated smaller project footprint of 29 km2 using three CO2 injection wells. Relatively homogenous reservoirs elsewhere in the assessment area have lower storage efficiencies due to a lack of intraformational seals within the Algebuckina Sandstone and have an associated larger project area of 49 km2 using three CO2 injection wells. Pressure management requirements are likely to be minimal in both model areas due to the thick and open nature of reservoirs. However, water production rates of up to 16,500 m3/day may be required where local lateral barriers to pressure dissipation occur.
Results from the AFER Project's GSC assessment demonstrate the value of applying a play-based exploration workflow for a regional-scale energy resource assessment. Estimating the geological probability of success to the presence and repeatability of four mappable risk elements associated with GSC resources allows both relative prospectivity maps and risked EUS volumes to be generated. Prospectivity maps and EUS volumes can in turn be readily updated as new geological data are collected to infill data and knowledge gaps. Geoscience Australia is building a national inventory of GSC resources using this play-based exploration approach, with qualitative assessments now completed under the EFTF and TEGI programs in seven basin areas from central and eastern Australia.
