Questions often asked by the public in regard to the concept of CO2 storage include; "But won?t it leak?", and "How long will it stay down there?". The natural environment of petroleum systems documents many of the processes which will influence CO2 storage outcomes, and the likely long (geological) timeframes that will operate. Thousand of billions of barrels of hydrocarbons have been trapped and stored in geological formations in sedimentary basins for 10s to 100s of millions of years, as has substantial volumes of CO2 that has been generated through natural processes. Examples from Australia and major hydrocarbon provinces of the world are documented, including those basins with major accumulations that are currently trapped in their primary reservoir, those that have accumulated hydrocarbons in the primary reservoir and then through tectonic activity spilled them to other secondary traps or released the hydrocarbons to the atmosphere, and those that generated hydrocarbons but for which no effective traps were in place for hydrocarbons to accumulate. Some theoretical modelling of the likelihood of meeting stabilisation targets using geological storage are based on leakage rates which are implausibly high when compared to observations from viable storage locations in the natural environment, and do not necessarily account for the likelihood of delay times for leakage to the atmosphere or the timeframe in which geological events will occur. Without appropriate caveats, they potentially place at risk the public perception of how efficient and effective appropriately selected geological reservoirs could be for storage of CO2. If the same rigorous methods, technology and skills that are used to explore for, find and produce hydrocarbon accumulations are now used for finding safe and secure storage sites for CO2, the traps so identified can be expected to contain the CO2 after injection for similar periods of time as that in which hydrocarbons and CO2 have been stored in the natural environment.

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.

This paper briefly summaries how intrinsic uncertainties in reservoir characterization, at the proposed Otway Basin Naylor Field carbon-dioxide geo-sequestration site, were risk managed by a process of creation and evaluation of a series of geo-models (term to describe the geo-cellular geological models created by PETREL software) that cover the range of plausible geological possibilities, as well as extreme case scenarios. Optimization methods were employed, to minimize simulation run time, whilst not compromising the essential features of the basic geo-model. For four different Cases, 7 geo-models of the reservoir were created for simulation studies. The reservoir simulation study relies primarily on production history matching and makes use of all available information to help screen and assess the various geo-models. The results suggest that the bulk reservoir permeability is between 0.5 - 1Darcy, the original gas-water-contact was about 2020 mSS and there is a strong aquifer drive.

Many industries and researchers have been examining ways of substantially reducing greenhouse gas emissions. No single method is likely to be a panacea, however some options do show considerable promise. Geological sequestration is one option that utilises mature technology and has the potential to sequester large volumes of CO2. In Australia geological sequestration has been the subject of research for the last 2? years within the Australian Petroleum Cooperative Research Centre's GEODISC program. A portfolio of potential geological sequestration sites (?sinks?) has been identified across all sedimentary basins in Australia, and these have been compared with nearby known or potential CO2 emission sources. These sources have been identified by incorporating detailed analysis of the national greenhouse gas emission databases with other publicly available data, a process that resulted in recognition of eight regional emission nodes. An earlier generic economic model for geological sequestration in Australia has been updated to accommodate the changes arising from this process of ?source to sink? matching. Preliminary findings have established the relative attractiveness of potential injection sites through a ranking approach. It includes the ability to accommodate the volumes of sequesterable greenhouse gas emissions predicted for the adjacent region, the costs involved in transport, sequestration and ongoing operations, and a variety of technical geological risks. Some nodes with high volumes of emissions and low sequestration costs clearly appear to be suitable, whilst others with technical and economic issues appear to be problematic. This assessment may require further refinement once findings are completed from the GEODISC site-specific research currently underway.

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. The geological analysis produced an assessment from over 100 potential Environmentally Sustainable Sites for CO2 Injection (ESSCI) by applying a deterministic risk assessment. Out of 100 potential sites, 65 proved to be valid sites for further study. This assessment examined predominantly saline reservoirs which is where we believe Australia?s greatest storage potential exists. However, many of these basins also contain coal seams that may be capable of storing CO2. Several of these coal basins occur close to coal-fired power plants and oil and gas fields where high levels of CO2 are emitted. CO2 storage in coal beds is intrinsically different to storage in saline formations, and different approaches need to be applied when assessing them. Whilst potentially having economic benefit, enhanced coal bed methane (ECBM) production through CO2 injection does raise an issue of how much greenhouse gas mitigation might occur. Even if only small percentages of the total methane are liberated to the atmosphere in the process, then a worse outcome could be achieved in terms of greenhouse gas mitigation. The most suitable coal basins in Australia for CO2 storage include the Galilee, Cooper and Bowen-Surat basins in Queensland, and the Sydney, Gunnedah, and Clarence-Moreton Basins in New South Wales. Brief examples of geological storage within saline aquifers and coal seams in the Bowen and Surat basins, Queensland Australia, are described in this paper to compare and contrast each storage option.

In March and April, 2012, Geoscience Australia undertook a seabed characterisation survey, aimed at supporting the assessment of CO2 storage potential of the Vlaming Sub-basin, Western Australia. The survey, undertaken as part of the National CO2 Infrastructure Plan program was targeted to provide an understanding of the link between the deep geological features of the area and the seabed, and connectivity between them as possible evidence for seal integrity. Data was acquired in two sections of the Rottnest Shelf lying above the regional seal - the South Perth Shale - and the underlying potentially CO2-suitable reservoir, the Gage Sandstone. Seabed samples were taken from 43 stations, and included 89 seabed grab samples. A total of 653 km2 of multibeam and backscatter data was obtained. Chirper shallow sub-bottom profile data was acquired concurrently. 6.65 km2 of side-scan sonar imagery was also obtained. The two surveyed areas, (Area 1 and Area 2), are set within a shallow sediment starved shelf setting. Area 2, situated to the southwest of Rottnest Island, is characterised by coralline red algal (rhodolith) beds, with ridges and mounds having significant rhodolith accumulations. The geomorphic expression of structural discontinuities outcropping at the seabed is evident by the presence of linear fault-like structures notable in Area 1, and north-south trending lineaments in Area 2. North-south trending structural lineaments on the outer section of Area 2 have in places, mounds standing 4-5 m above the seafloor in water depths of 80-85 m. Although there are apparent spatial correlations between seabed geomorphology and the structural geology of the basin, the precise relationship between ridges and mounds that are overlain by rhodolith accumulations, fluid seepage, and Vlaming Sub-basin geology is uncertain, and requires further work to elucidate any links.

The presence of abundant bedded sulfate deposits before 3.2 Ga and after 1.8 Ga, the peak in iron formation abundance between 3.2 and 1.8 Ga, and the aqueous geochemistry of sulfur and iron together suggest that the redox state, and the abundances of sulfur and iron in the hydrosphere varied widely during the Archean and Proterozoic. We propose a layered hyddrosphere prior to 3.2 Ga in which sulfate produced by atmospheric photolytic reactions was enriched in an upper layer, whereas the underlying layer was reduced and sulfur-poor. Between 3.2 and 2.4 Ga, biolotical and/or inorganic sulfate reduction reactions removed sulfate from the upper layer, producing broadly uniform, reduced, sulfur-poor and iron-rich oceans. As a result of increasing atmospheric oxygenation around 2.4 Ga, the flux of sulfate into the hydrosphere by oxidative weathering was greatly enhanced, producing layered oceans, with sulfate-rich, iron-poor surface waters and reduced, sulfur-poor and iron-rich bottom waters. This process continued so that by 1.8 Ga, the hydrosphere was generally oxidized, sulfate-rich and iron-poor throughout. Variations in sulfur and iron abundances suggest that the redox state of the oceans was buffered by iron before 2.4 Ga and by sulfur after 1.8 Ga.

A question and answer style brochure on geological storage of carbon dioxide. Questions addressed include: - What is geological storage? - Why do we need to store carbon dioxide? - How can you store anything in solid rock? - Could the carbon dioxide contaminate the fresh water supply? - Could a hydrocarbon seal leak? - Are there any geological storage projects in Australia?

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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.