Executive summary
A regional geological carbon storage (GCS) screening study was conducted for the Shipwreck Trough, located offshore in the Otway Basin, to assess the feasibility of long-term CO₂ storage. The study employed 2D basin modelling along three seismic transects, integrating seismic interpretation, well data, and geochemical analyses to evaluate storage capacity, containment risks, and key geological factors essential for the safe and effective storage of CO₂.
Study objectives and methodology
The primary objectives were to:
→ Identify and characterize potential storage intervals and sites.
→ Assess regional storage capacity and sealing integrity.
→ Understand geological risks including fault reactivation, pressure regimes, and containment security.
A comprehensive tectono-stratigraphic framework was developed to delineate aquifer and aquitard systems. Regional tectonics were analysed to evaluate the likelihood of fault reactivation and cross-fault fluid communication. A hydrodynamic assessment was conducted using well data (e.g., pressure, temperature, porosity, permeability, and water geochemistry) to refine understanding of storage unit behaviour.
2D basin modelling formed the core of the study, utilizing Geoscience Australia’s seismic interpretations and stratigraphic boundaries. Lithofacies assignment was calibrated using vitrinite reflectance, porosity, permeability, and pressure data. Several geological scenarios were tested to evaluate the influence of lithological variability on seal integrity and reservoir performance.
Key findings
→ Sealing units:
- The Belfast Mudstone and Skull Creek Mudstone are identified as the most regionally significant sealing formations. These thick, homogenous shale units—especially near the present-day shelf edge—exhibit high predicted CO₂ column height capacities, exceeding 300 m in the most favourable locations.
→ Storage potential:
→ The Waarre-Belfast/Skull Creek play, particularly in the area surrounding La Bella 1, Conan 1, and Thistle 1, emerged as the most promising. Waarre Formation sandstones exhibit favourable porosities (18–23%) and are overlain by thick seal units, supporting safe CO₂ containment at depths of 2000–3000 m.
→ The Thylacine-Belfast play, located farther offshore, is characterised by strong seal integrity but smaller aquifer size and higher overpressure risks, limiting its practical storage potential.
→ The Nullawarre-Belfast/Skull Creek play, closer to the coastline, presents several disadvantages over the previous two, including limited seal thickness, reduced burial, smaller aquifer size, and higher likelihood of CO₂ phase change due to shallow conditions—making it generally unsuitable for regional-scale CO₂ storage.
→ Hydrodynamic conditions:
- Modelling indicates hydrostatic pressure regimes in shallow inboard sections, with overpressure conditions more prevalent in distal offshore areas. The 1073 psi (7.4 MPa) isobar intersects the 31°C isotherm at approximately 740 m depth, marking the threshold below which CO₂ remains in a supercritical state—essential for long-term containment. Any potential leakage pathways connecting to shallower units pose a risk of CO₂ phase change and therefore must be avoided.
→ Fault behaviour:
- The risk of fault reactivation is higher along the proximal offshore areas, due to recent tectonic activity and shallow burial, compromising seal integrity. Farther outboard, faults are predicted to have lower transmissibility and higher sealing character, though further analysis—including critical stress and fault termination studies—is required to refine this assessment.
Conclusion
This GCS screening study has identified high-potential CO₂ storage plays within the offshore Shipwreck Trough, notably in the Waarre-Belfast/Skull Creek interval. These findings support continued CCS investigations in the Otway Basin, with an emphasis on offshore, deeper burial zones offering superior containment.
