To understand Victoria’s potential for underground hydrogen storage (UHS), the depleted, unproduced and repurposed fields of the Port Campbell Embayment were assessed for subsurface storage suitability. Additionally, the saline reservoir storage potential of the area was investigated. Data from historic exploration and previous studies in the Port Campbell Embayment were used to undertake geological investigations and storage capacity estimates. The fields investigated in this preliminary study have potential, with the Waarre Formation-Belfast Mudstone reservoir-seal pair highly favourable for UHS. Reservoir injectivity assessments suggest the existing fields are capable of multiple cycles of injection and withdrawal. Seal capacity analysis indicates that the Belfast Mudstone is capable of retaining column heights of hydrogen ranging from 55 to 1267 m, which mostly exceed the greatest known vertical closures in the onshore Otway Basin. The hydrogen storage capacity and injectivity results were used to rank the fields. The Iona field is the most prospective site, with an estimated working gas capacity of 9.1 petajoules (PJ). The total working gas capacity for hydrogen storage in the Port Campbell Embayment fields is approximately 42.7 PJ. Further storage in the area is possible within the Waarre saline reservoir play, with an estimated range of 50.7 to 202.7 PJ.

The Otway Basin is one of the best known and most actively explored of a series of Mesozoic basins formed along the southern coastline of Australia by the rifting of the Antarctic and Australian plates during the Cretaceous. The basin offers a diversity of play types, with at least three major sedimentary sequences forming conventional targets for petroleum exploration in the onshore basin. The Penola Trough in South Australia has enjoyed over 20 years of commercial hydrocarbon production from the sandstones of the Early Cretaceous Otway Group comprising the Crayfish Subgroup (Pretty Hill Formation and Katnook sandstones) and Eumeralla Formation (Windermere Sandstone Member). Lithostratigraphic characterisation and nomenclature for these sequences are poorly constrained, challenging correlation across the border into the potentially petroleum prospective Victorian Penola Trough region. The Geological Survey of Victoria (GSV), as part of the Victorian Gas Program, commissioned Chemostrat Australia to undertake an 11-well chemostratigraphic study of the Victorian Otway Basin. The South Australia Department for Energy and Mining, GSV and Chemostrat Australia are working collaboratively to develop a consistent, basin-wide schema for the stratigraphic nomenclature of the Otway Basin within a chemostratigraphic framework. Variability in the mineralogy and hence inorganic geochemistry of sediments reflects changes in provenance, lithic composition, facies changes, weathering and diagenesis. This geochemical variation enables the differentiation of apparently uniform sedimentary successions into unique sequences and packages, aiding in the resolution of complex structural relationships and facies changes. In this paper, we present the preliminary results of detailed geochemical analyses and interpretation of 15 wells from across the Otway Basin and the potential impacts on hydrocarbon prospectivity.

Time-lapse gravity surveys are a potential low cost method for detecting CO2 migration from a storage site, particularly where accumulation within an overlying aquifer is predicted. The modelled storage system consists of a storage reservoir (1000 m crestal depth) and an overlying aquifer at variable depths (50-750m crest), within a simple dome structure. In leakage scenarios, these are connected by a single vertical permeable pathway. CO2 leakage was simulated using the Permedia (R) CO2 simulator, and a gravity model calculated to compare a leakage and a non-leakage scenario. Time-lapse gravity surveys are likely to be able to detect CO2 leakage with CO2 accumulation within an aquifer to depths of at least 750 m, at least within an actively subsiding sedimentary basin where sandstones are expected to have high porosities at shallow burial depths. For a high relief structure in which the CO2 accumulates, the change in gravity cannot be used to detect the location of the leakage pathway as the measured gravity anomaly is centred on the geological structure. The first detection of leakage is possible after 11-15 years of leakage, though a maximum of only c. 1% of injected CO2 will have leaked at this time. (C) 2017 Elsevier Ltd. All rights reserved.

We combine reservoir simulation with 2D synthetic seismic reflection time-lapse data to assess the ability of seismic methods to image plume growth, evolution, and migration within a heterogeneous saline reservoir. The incorporation of reservoir heterogeneity results in a range of saturations due to the tortuous migration around the intra-reservoir baffles. To account for the disruptive nature of the injected CO2, and the uncertainties regarding the fluid saturation distribution, we use two end-member models, uniform and patchy, to generate the widest range of seismic velocity distributions to understand the range of velocity-saturation behaviour which could be encountered. The generated seismic sections show clear differences between the two models while also providing confidence in the ability to detect CO2 plume growth and evolution in the reservoir. A free-phase migrating front of CO2 appears to be difficult to detect, however. The ability to image a front is shown to be dependent not only on the pore-fluid saturation distribution - patchy or uniform - but also on its larger-scale spatial geometry. As the subtle change in amplitude is directly related to the concentration of CO2 within each accumulation, it suggests that the saturation model has important implications for CO2 detectability and for quantifying the volume of CO2 injected into the reservoir. (C) 2015 Elsevier Ltd. All rights reserved.

Subsurface monitoring is essential for the successful implementation and public acceptance of CO2 storage. Injected CO2 will need to be monitored to verify the successful containment within its intended formation, and to ensure no loss of containment within the storage complex. The ability for seismic techniques to monitor structurally trapped CO2 has been successfully demonstrated due to the changes in the acoustic properties of the reservoir produced by the displacement of brine by less dense and more compressible CO2. However, the ability for seismic methods to detect free-phase migrating CO2 is still moderately understood. In order to assess the feasibility for seismic monitoring of a migrating front, we estimate the time-lapse signal over a theoretical, clean, homogeneous sandstone reservoir through the application of a three-stage model-driven workflow consisting of fluid-flow, rock physics and seismic forward modelling. To capture the range of responses which could be encountered, two end-member fluid distribution models were used: uniform saturation and the modified patchy saturation model. Analysis of the time- lapse survey highlights the importance of determining and understanding the fluid distribution model impacting the range of velocities prior to generating and interpreting the seismic response. This change in velocity is shown to be directly related to the volume of CO2 occupying the pore-space of a migrating plume front. This highlights the fact that the detectability of a migrating front is a site specific issue which not only depends on the geophysical parameters of the seismic survey but also on the geological variations and spatial distribution in the reservoir.