The CO2CRC Otway Project in southwestern Victoria is the Australian flagship for geological storage of CO2. Phase 1 of the project involved the injection of a CO2-rich supercritical fluid into a depleted natural gas field at a depth of ~2 km. The project reached a major milestone late last year with the cessation of injection and the emplacement of around 65,000 tonnes of the supercritical fluid. Phase 2 of the project is set to commence in early 2011 with the injection a few 100 tonnes of pure CO2 into a saline aquifer at ~1.5 km depth. Critical to the project was the drilling of the CRC-1 and CRC-2 wells, with both being used as injection wells. During drilling of each well, fluorescein dye was added to the drilling mud with the intention to maintain a concentration of 5 ppm w/v. The role of fluorescein was to 1) quantitated the degree of drilling fluid contamination that may accompany autochonthous formation waters recovered with the multiple dynamic testing (MDT) tool, and 2) provide a measure of the depth of drilling mud penetration into the recovered cores in order to provide pristine material for microbiological studies.

Matching of CO2 emission sources with storage opportunities or source/sink matching (SSM), involves the integration of a number of technical, social and economic issues. It requires identification of the optimal locations for both the emission source and storage site for CO2 emissions. The choice of optimal sites is a complex process and will not rest solely on the best technical site for storage, but will require a detailed assessment of source issues, transport links and integration with economic and environmental factors. Transport is one of the major costs in CO2 sequestration and in many instances it will strongly influence how locations are chosen, but itself will be dependent on what type of facilities are to be built, be they either onshore or offshore or a combination of both. Comparison of theoretical studies, and the numerous criteria they utilise in their assessments, with current or planned commercial operations indicates that it is only a few of the major criteria that determine site locations.

The geological storage of carbon dioxide (CO2) is the process whereby CO2 captured from power plants or other industrial facilities is transported by pipeline to a suitable location and then injected under pressure into a deep geological reservoir formation, where it remains permanently trapped and prevented from entering the atmosphere. The processes by which it is retained in the subsurface are generally those that have trapped oil, gas and naturally generated CO2 for millions of years. The geological formations that can be utilised for this trapping have the same characteristics as those that are able to act as reservoir rocks for petroleum. They have good porosity and permeability and have an overlying sealing formation, which will prevent the trapped fluids migrating out of the storage reservoir and possibly escaping to the surface. In addition, because of the phase behaviour of CO2, efficient storage requires that they are stored at depths greater than 800 below the surface. Unlike oil and gas, which rely primarily on a three dimensional structural trap to prevent them from ultimately rising to the surface, there are additional trapping mechanisms for CO2. Given a sufficiently long migration path within a formation, CO2 will ultimately be rendered immobile by dissolution into the formation water, residual trapping and potentially, over longer time scales, mineralisation. As groundwaters at these depths are generally saline, this type of storage is often termed deep saline aquifer storage. A recent nationwide review by Commonwealth and State geological surveys, as part of the Carbon Storage Taskforce, rated the suitability of geological basins across Australia for geological storage of CO2. The most geologically suitable basins are the offshore Gippsland and North Perth basins but several onshore basins also rate highly. These include the Eromanga, Cooper, Bowen, Galilee, Surat, Canning and Otway basins. The Victorian Government has recently released area for greenhouse gas storage exploration in the Gippsland Basin and the Queensland Government in the Galilee and Surat basins. The aquifers within these basins provide groundwater for human consumption, agriculture, mining, recreation and groundwater dependent ecosystems. The Surat Basin also contains oil and gas accumulations that are being exploited by the onshore petroleum industry. Understanding the existing the groundwater's chemistry and the connectivity between aquifers in the context of its current use is essential in order to determine whether prospective aquifers could be used for geological storage of CO2 without compromising other activities. The potential risks to groundwater from the potential migration of CO2 and changes to groundwater properties that might be expected will also be discussed. Current data gaps include poor hydrogeochemical data coverage for the deeper aquifers and particularly limited data on trace metals and organics. A comparison with experiences learned from enhanced oil recovery using CO2 in North America and the CO2CRC's pilot CO2 injection project in Western Victoria will illustrate some of the unique differences and opportunities for geological storage of CO2 in Australia. Oral presentation at "Groundwater 2010" conference, 31 October - 4th November 2010, Canberra

Geoscience Australia is conducting a study under the National Carbon Infrastructure Plan (NCIP) to assess the suitability of the Vlaming Sub-basin for CO2 storage. It involves characterisation of the Valanginian reservoir (Gage Sandstone) and the Early Cretaceous seal (South Perth Shale) by integrating seismic interpretation and well log analysis in a detailed sequence stratigraphic investigation. The Gage Sandstone, comprised of channelised turbidites and mass flows, was the first unit deposited after breakup between India and Australia. Deposited during a sea level lowstand in the palaeo-topographic lows of the breakup unconformity, it is overlain by a thick deltaic to shallow marine succession of the South Perth Shale. The Gage Sandstone is considered one of the best reservoirs in the sub-basin with porosities of 23-30% and permeabilities of 200-1800 mD. It occurs at depths between 1000 and 3000 m below the seafloor, which makes, it an attractive target for the injection and long-term storage of supercritical CO2. The new extent of the Gage Sandstone, based on seismic interpretation and well log correlation, shows that in some of the wells the sandstone unit overlying the Valanginian unconformity belongs to the South Perth Shale and not to the Gage Sandstone. The G. Mutabilis palynological zone used in the past for identifying Gage Sandstone interval appears to be facies controlled and time transgressive. Detailed analysis of the reservoir properties at the wells in conjunction with systematic seismic facies mapping will serve as a basis for a regional reservoir model and storage potential estimation of the Gage Sandstone reservoir.

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.

Geological Storage Potential of CO2 & Source to Sink Matching Matching of CO2 sources with CO2 storage opportunities (known as source to sink matching), requires identification of the optimal locations for both the emission source and storage site for CO2 emissions. The choice of optimal sites is a complex process and can not be solely based on the best technical site for storage, but requires a detailed assessment of source issues, transport links and integration with economic and environmental factors. Many assessments of storage capacity of CO2 in geological formations have been made at a regional or global level. The level of detail and assessment methods vary substantially, from detailed attempts to count the actual storage volume at a basinal or prospect level, to more simplistic and ?broad brush? approaches that try to estimate the potential worldwide (Bradshaw et al, 2003). At the worldwide level, estimates of the CO2 storage potential are often quoted as ?very large? with ranges for the estimates in the order of 100?s to 10,000?s Gt of CO2 (Beecy and Kuuskra, 2001; Bruant et al, 2002; Bradshaw et al 2003). Identifying a large global capacity to store CO2 is only a part of the solution to the CO2 storage problem. If the large storage capacity can not be accessed because it is too distant from the source, or is associated with large technical uncertainty, then it may not be possible to reliably predict that it would ever be of value when making assessments. To ascertain whether any potential storage capacity could ever be actually utilised requires analysis of numerous other factors. Within the GEODISC program of the Australian Petroleum Cooperative Research Centre (APCRC), Geoscience Australia (GA) and the University of New South Wales (UNSW) completed an analysis of the potential for the geological storage of CO2. Over 100 potential Environmentally Sustainable Sites for CO2 Injection (ESSCIs) were assessed by applying a deterministic risk assessment (Bradshaw et al, 2002). At a regional scale Australia has a risked capacity for CO2 storage potential in excess of 1600 years of current annual total net emissions. However, this estimate does not incorporate the various factors that are required in source to sink matching. If these factors are included, and an assumption is made that some economic imperative will apply to encourage geological storage of CO2, then a more realistic analysis can be derived. In such a case, Australia may have the potential to store a maximum of 25% of our total annual net emissions, or approximately 100 - 115 Mt CO2 per year.

The Petrel Sub-basin Marine Environmental Survey GA-0335, (SOL5463) was acquired by the RV Solander during May 2012 as part of the Commonwealth Government's National Low Emission Coal Initiative (NLECI). The survey was undertaken as a collaboration between the Australian Institute of Marine Science (AIMS) and GA. The purpose was to acquire geophysical and biophysical data on shallow (less then 100m water depth) seabed environments within two targeted areas in the Petrel Sub-basin to support investigation for CO2 storage potential in these areas.

There remains considerable uncertainty regarding the location, timing and availability of CO2 storage sites in both southeast Queensland and New South Wales. In New South Wales, the main issues relate to the lack of recent or reliable valid geological information that would permit a complete and comprehensive evaluation. Some sedimentary basins appear to contain potential storage reservoirs although they have low permeabilities, and are therefore likely to have low injection rates. In southeast Queensland, recent work has indicated that in some parts of the Bowen and Surat basins CO2 storage is likely to compete with other resources such as groundwater and hydrocarbons. However, current research on the potential storage in deeper saline formations in the southern and western Bowen Basin has provided encouraging results. Storage in deeper stratigraphic units in the central western part of the basin will rely on injection in low permeability formations, and more correlation work is required to define generally narrow storage targets. The Wunger Ridge, in the southern Bowen Basin, however, has promise with both significant storage potential and relatively low geological risk. One area in which there is some potential in both New South Wales and southeast Queensland is CO2 storage in coal seams, as close technical and economic relationships exist between coal bed methane (CBM) field development and operations and CO2 storage. Substantial collaborative research is still required in this area and is currently a focus of the CO2CRC activities

Between 3 May 2012 to 24 June 2012 Geoscience Australia undertook two major surveys off the coast of the Northern Territory in the Petrel Sub-Basin. The data acquisition was funded through the National Low Emissions Coal Initiative (NLECI) and the Petrel Sub-basin was selected in particular as it has been identified as a prospective area for CO2 storage. One of these surveys, GA336 acquired 4091 kilometres of 2D seismic reflection data. Following on from the completion of the seismic processing of this data was further investigative work investigative work such as this analysis. Four prime lines, GA336-107, 110, 205 and 207 along with the well logs, Flat-Top1, Petrel 1A and Petrel 4 were selected for further 2D Simultaneous Inversion and Rock Physics Modelling. Previous Pre Stack Depth Migration had been undertaken on these lines and the PSDM Angle Stacks were imported along with the relevant horizon interpretation into the Jason integration algorithms.

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