This report details the suitability of two identified sites in the Browse Basin for the geological storage of carbon dioxide: the Carbine Ponded Turbidite and the Leveque Shelf long migration dissolution trap. Detailed site assessments were completed by undertaking detailed geophysical interpretation of the top and base of each site, combined with a comprehensive structural, stratigraphic and sedimentological analysis, in order to construct a series of static 3D reservoir models for each potential storage site. These were submitted for CO2 injection simulation in order to better estimate the potential storage capacity, the potential injectivity volumes, and identify any containment-related issues of each site. Therefore this reports aims to provide technical recommendations regarding the viability of the long-term geological storage of CO2 in the Browse Basin.

As part of the Australian Government National CO2 Infrastructure Plan (NCIP), Geoscience Australia is undertaking CO2 storage assessment of the Vlaming Sub-basin located offshore Western Australia in the southern Perth Basin. The Vlaming Sub-basin is a Mesozoic depocentre containing up to 14 km of sediments. Close proximity of the basin to industrial polluters in the Perth area dictates the need to find CO2 storage solutions in this basin. The main reservoir unit identified as suitable for storage of CO2 is the Early Cretaceous Gage Sandstone deposited in paleo-topographic lows of the Valanginian breakup unconformity. The reservoir unit is laterally extensive (over 1,500 km2) and over most of the area reasonably thick (100 - 300 m). It lies at depths between 1400 and 2000 m below the seafloor, which is suitable for injection of the supercritical CO2 and makes it an attractive target for the long-term storage. The reservoir unit is overlain by a thick deltaic to shallow marine succession of the South Perth Shale, which represents a regional seal in the area. Carbon Storage taskforce estimated that up 1 GT of CO2 can be stored in the Gage Sandstone. The first assessment of the Vlaming Sub-basin undertaken by CO2CRC focused on evaluation of the reservoir unit and overall storage capacity. The current study is based on interpretation and integration of the seismic, well and marine datasets, both existing and acquired since the previous assessment. It includes detailed analysis of reservoir and seal properties and a comprehensive evaluation of the seal integrity risks to allow a more accurate and realistic modeling for CO2 storage.

Introduction This National Carbon Infrastructure Plan study assesses the suitability of the Vlaming Sub-basin for CO2 storage. The Vlaming Sub-basin is a Mesozoic depocentre within the offshore southern Perth Basin, Western Australia (Figure 1). It is around 23,000 km2 and contains up to 14 km of sediments. The Early Cretaceous Gage Sandstone was deposited in paleo-topographic lows of the Valanginian breakup unconformity and is overlain by the South Perth Shale regional seal. Together, these formations are the most prospective reservoir/seal pair for CO2 storage. The Gage Sandstone reservoir has porosities of 23-30% and permeabilities of 200-1800 mD. It lies mostly from 1000 - 3000 m below the seafloor, which is suitable for injection of supercritical CO2 and makes it an attractive target as a long-term storage reservoir. Methods & datasets To characterise the Gage reservoir, a detailed sequence stratigraphic analysis was conducted integrating 2D seismic interpretation, well log analysis and new biostratigraphic data (MacPhail, 2012). Paleogeographic reconstructions of components of the Gage Lowstand Systems Tract (LST) are based on seismic facies mapping, and well log and seismic interpretations. Results The Gage reservoir is a low stand systems tract that largely coincides with the Gage Sandstone and is defined by the presence of the lower G. mutabilis dinoflagellate zone. A palynological review of 6 wells led to a significant revision, at the local scale, of the Valanginian Unconformity and the extent of the G. mutabilis dinoflagellate zones (MacPhail, 2012). G. mutabilis dinoflagellates were originally deposited in lagoonal (or similar) environments and were subsequently redeposited in a restricted marine environment via mass transport flows. Mapping of the shelf break indicates that the Gage LST was deposited in water depths of >400 m. Intersected in 8 wells, the Gage LST forms part of a sand-rich submarine fan system (Figure 2) that includes channelized turbidites, low stand fan deposits, debris flows (Table 1). This interpretation is broadly consistent with Spring & Newell (1993) and Causebrook (2006). The Gage LST is thickest (up to 360 m) at the mouth of large canyons adjacent to the Badaminna Fault Zone (BFZ) and on the undulating basin plain west of Warnbro 1 (Figure 1). Paleogeographic maps depict the evolution of the submarine fan system (Figure 3). Sediment transport directions feeding the Gage LST are complex. Unit A is sourced from the northern canyon (Figure 3a). Subsequently, Unit B (Figure 3b) derived sediment from multiple directions including incised canyons adjacent to BFZ and E-W oriented canyons eroding into the Badaminna high. These coalesce on an undulating basin plain west of Warnbro 1. Minor additional input for the uppermost Unit C (Figure 3c) is derived from sources near Challenger 1. Summary 1: The Gage LST is an Early Cretaceous submarine fan system that began deposition during the G. mutabilis dinoflagellate zone. It ranges from confined canyon fill to outer fan deposits on an undulating basin plain. 2: The 3 units within the Gage LST show multidirectional sediment sources. The dominant supply is via large canyons running north-south adjacent to the Badaminna Fault Zone. 3: Seismic facies interpretations and palaeogeographic mapping show that the best quality reservoirs for potential CO2 storage are located in the outer fan (Unit C sub-unit 3) and the mounded canyon fill (Unit A). These are more likely to be laterally connected. 4: The defined units and palaeogeographic maps will be used in a regional reservoir model to estimate the storage capacity of the Gage LST reservoir.

Geoscience Australia is investigating the suitability of offshore sedimentary basins as potential CO2 storage sites. In May 2012 a seabed survey (GA0335/SOL5463) was undertaken in collaboration with the Australian Institute of Marine Science to acquire baseline marine data in the Petrel Sub-basin, Joseph Bonaparte Gulf. The aim was to collect information on possible connections (faults and fluid pathways) between the seabed and key basin units, and to characterise seabed habitats and biota. Two areas were surveyed (Area 1: 471 km2, depth ~ 80-100 m; Area 2: 181 km2, depth ~ 30-70 m), chosen to investigate the seabed over the potential supercritical CO2 boundary (Area 1) and the basin margin (Area 2), with Area 2 located around Flat Top 1 Well. Data analysed include multibeam sonar bathymetry and backscatter, seabed samples and their geochemical and biological properties, video footage and still images of seabed habitats and biota, and acoustic sub-bottom profiles. Pockmarks, providing evidence for fluid release, are present at the seabed, and are particularly numerous in Area 1. Area 1 is part of a sediment-starved, low-relief section of shelf characterised by seabed plains, relict estuarine paleochannels, and low-lying ridges. Facies analysis and radiocarbon dating of relict coastal plain sediment indicates Area 1 was a mangrove-rich environment around 15,500 years ago, transgressed near the end of the Last Glacial period (Meltwater Pulse 1A). Modern seabed habitats have developed on these relict geomorphic features, which have been little modified by recent seabed processes. Seabed habitats include areas of barren and bioturbated sediments, and mixed patches of sponges and octocorals on hardgrounds. In the sub-surface, stacked sequences of northwest-dipping to flat-lying, well-stratified sediments, variably incised by palaeochannels characterise the shallow geology of Area 1. Some shallow faulting through these deposits was noted, but direct linkages between seabed features and deep-seated faults were not observed. Area 2 is dominated by carbonate banks and ridges. Low-lying ridges, terraces and plains are commonly overlain by hummocky sediment of uncertain origin. Pockmarks are present on the margins of banks, and on and adjacent to ridges. Despite the co-location of banks and ridges with major faults at depth, there is a lack of direct evidence for structural connectivity, particularly because of significant acoustic masking in the sub-surface profiles of Area 2. While no direct structural relationship was observed in the acoustic sub-bottom profiles between these banks, ridges and faults visible in the basin seismic profiles, some faults extend through the upper basin units towards the seabed on the margin of Area 2. No evidence was detected at the seabed for the presence of thermogenic hydrocarbons or other fluids sourced from the basin, including beneath the CO2 supercritical boundary. The source of fluids driving pockmark formation in Area 1 is most likely decomposing mangrove-rich organic matter within late Pleistocene estuarine sediments. The gas generated is dominated by CO2. Additional fluids are potentially derived from sediment compaction and dewatering. Conceptual models derived from this are being used to inform regional-scale assessments of CO2 storage prospectivity in the Petrel Sub-basin.

In 2011 as part of the National CO2 Infrastructure Plan (NCIP), Geoscience Australia started a three year project to provide new pre-competitive data and a more detailed assessment of the Vlaming Sub-basin prospectivity for the storage of CO2. Initial assessment by Causebrook 2006 of this basin identified Gage Sandstone and South Perth Shale (SPS) formations as the main reservoir/seal pair suitable for long-term storage of CO2. SPS is a thick (1900 m) deltaic succession with highly variable lithologies. It was estimated that the SPS is capable of holding a column of CO2 of up to 663m based on 6 MICP tests (Causebrook, 2006). The current study found that sealing capacity of the SPS varies considerably across the basin depending on what part of the SPS Supersequence is present at that location. Applying a sequence-stratigraphic approach, the distribution of mudstone facies within the SPS Supersequence, was mapped across the basin. This facies is the effective sub-regional seal of the SPS. Analysis of the spatial distribution and thickness of the effective seal is used for characterisation of the containment potential in the Vlaming Sub-basin CO2 storage assessment.

The Vlaming Sub-basin Marine Survey GA-0334 was undertaken in March and April 2012 as part of the Commonwealth Government's National CO2 Infrastructure Plan (NCIP). The purpose was to acquire geophysical and biophysical data to help identify sites suitable for the long term storage of CO2 within reasonable distances of major sources of CO2 emissions. This dataset contains identifications of animals collected from 32 Van Veen grabs deployed during GA-0334. Sediment was elutriated for ~ 5 minutes over a 500um sieve. Retained sediments and animals were then preserved in 70% ethanol for later laboratory sorting and identification (see `lineage'). During sorting, all worms were separated and sent to Infaunal Data Pty Ltd (Lynda Avery) for identification to species or operational taxonomic unit (OTU). Lynda Avery completed identifications on 17 April 2013, and specimens were lodged at the Museum of Victoria. All other taxa were identified to morphospecies at GA by an ecologist. Gray shading indicates taxa identified to species level by Lynda Avery (Refer to GeoCat # 76463 for raw data of species identifications by taxonomist); all other taxa were identified to morphospecies. Data is presented here exactly as delivered by the taxonomist/ecologist, and Geoscience Australia is unable to verify the accuracy of the taxonomic identifications. Stations are named XXGRYY where XX indicates the station number, GR indicates Van Veen grabs, and YY indicates the sequence of grabs deployed (i.e. the YYth grab on the entire survey). H indicates heavy fraction animals and HS indicates animals found on a sponge. The dataset is current as of November 2014, but will be updated as taxonomic experts contribute. See GA Record 2013/09 for further details on survey methods and specimen acquisition.

Atmospheric tomography is a monitoring technique that uses an array of sampling sites and a Bayesian inversion technique to simultaneously solve for the location and magnitude of a gaseous emission. Application of the technique to date has relied on air samples being pumped over short distances to a high precision FTIR Spectrometer, which is impractical at larger scales. We have deployed a network of cheaper, less precise sensors during three recent large scale controlled CO2 release experiments; one at the CO2CRC Ginninderra site, one at the CO2CRC Otway Site and another at the Australian Grains Free Air CO2 Enrichment (AGFACE) facility in Horsham, Victoria. The purpose of these deployments was to assess whether an array of independently powered, less precise, less accurate sensors could collect data of sufficient quality to enable application of the atmospheric tomography technique. With careful data manipulation a signal suitable for an inversion study can be seen. A signal processing workflow based on results obtained from the atmospheric array deployed at the CO2CRC Otway experiment is presented.

Abstract for submission to 11th IEA GHG International Conference on Greenhouse Gas Control Technologies. Conference paper to follow pending selection for oral or poster presentation. Abstract covers the GA-ACCA21 China Australia Geological Storage of CO2 (CAGS) Project run through PMD/ED 2009-2012.

Identification of major hydrocarbon provinces from existing world assessments for hydrocarbon potential can be used to identify those sedimentary basins at a global level that will be highly prospective for CO2 storage. Most sedimentary basins which are minor petroleum provinces and many non-petroliferous sedimentary basins will also be prospective for CO2 storage. Accurate storage potential estimates will require that each basin be assessed individually, but many of the prospective basins may have ranges from high to low prospectivity. The degree to which geological storage of CO2 will be implemented in the future will depend on the geographical and technical relationships between emission sites and storage locations, and the economic drivers that affect the implementation for each source to sink match. CO2 storage potential is a naturally occurring resource, and like any other natural resource there will be a need to provide regional access to the better sites if the full potential of the technology is to be realized. Whilst some regions of the world have a paucity of opportunities in their immediate geographic confines, others are well endowed. Some areas whilst having good storage potential in their local region may be challenged by the enormous volume of CO2 emissions that are locally generated. Hubs which centralize the collection and transport of CO2 in a region could encourage the building of longer and larger pipelines to larger and technically more viable storage sites and so reduce costs due to economies of scale.

In May 2013, Geoscience Australia (GA) and the Australian Institute of Marine Science (AIMS) undertook a collaborative seabed mapping survey (GA0340/ SOL5754) on the Leveque Shelf, a distinct geological province within the Browse Basin, offshore Western Australia. The purpose of the survey was to acquire geophysical and biophysical data on seabed environments over a previously identified potential CO2 injection site to better understand the overlying seabed habitats and to assess potential for fluid migration to the seabed. Mapping and sampling was undertaken across six areas using multibeam and single beam echosounders, sub-bottom profilers, sidescan sonar, underwater towed-video, gas sensors, water column profiler, grab samplers, and vibrocorer. Over 1070 km2 of seabed and water column was mapped using the multibeam and single beam echosounder, in water depths ranging between 40 and 120 m. The sub-surface was investigated using the multichannel and the parametric sub-bottom profilers along lines totalling 730 km and 1547 km in length respectively. Specific seabed features were investigated over 44 line km using the sidescan sonar and physically and sampled at 58 stations. Integration of this newly acquired data with existing seismic data will provide new insights into the geology of the Leveque Shelf. This work will contribute to the Australian Government's National CO2 Infrastructure Plan (NCIP) by providing key seabed environmental and geological data to better inform the assessment of the CO2 storage potential in this area of the Browse Basin. This dataset contains identifications of Polychaetes collected from 64 Smith-McIntyre grabs deployed during GA0340/SOL5754.