MAPPING GEOLOGICAL STORAGE PROSPECTIVITY OF CO 2 FOR THE WORLD S SEDIMENTARY BASINS AND REGIONAL SOURCE TO SINK MATCHING John Bradshaw 1*, Tess Dance 1 1 Greenhouse Gas Technologies Cooperative Research Centre (CO2CRC) & Geoscience Australia GPO Box 378, Canberra, ACT, 2601. ABSTRACT 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 CO 2 storage. Most sedimentary basins which are minor petroleum provinces and many non-petroliferous sedimentary basins will also be prospective for CO 2 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 CO 2 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. CO 2 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 CO 2 emissions that are locally generated. Hubs which centralize the collection and transport of CO 2 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. INTRODUCTION There have been several attempts to estimate the world s total storage potential for CO 2 in terms of capacity [1], but no maps of the global distribution of the most likely areas for CO 2 storage have been published. Part of the reason for this is the immaturity of the science of CO 2 storage and the uncertainties associated with delivering such an output. However, by comparing detailed assessments that have been done in a few locations at a country level, with world wide datasets for assessing hydrocarbon potential (a different but very relevant technology), it is possible to make a first pass estimate of where the worlds CO 2 storage potential might be located. By overlaying this geological data with the locations of the world s current large stationary energy CO 2 emissions point sources [2] insights can be obtained as to which regions will be likely to provide the most technically and economically viable CO 2 storage sites. AUSTRALIAN AND UNITED STATES GEOLOGICAL SURVEY (USGS) DATASETS As part of the GEODISC program in Australia an assessment was made of the CO 2 storage potential of 100 possible storage sites, from 48 basins [3]. Over 300 sedimentary basins are recognized in Australia, however by applying several screening criteria, the number of basins with some prospectivity was reduced to 48. Out of the 100 potential sites, 65 appeared to have viable geological parameters. The data from these sites were compared to emission profiles and source locations and the data input to an economic model to produce a range of costs for each site. From the integration of this analytical data, matches were made of sources and sinks. Conclusions of the suitability of CO 2 storage in different basin and trap types was a significant output from this project that can be applied at a global level. * Corresponding author: Tel. +61 (0)2 62499659, Fax.+61 (0)2 62499980, Email: John.Bradshaw@ga.gov.au
The United States Geological Survey (USGS) periodically undertakes a world wide assessment of the potential for hydrocarbon prospectivity [4]. This includes assessing all sedimentary basins around the world and predicting future hydrocarbon discoveries from both known and frontier petroleum provinces. The USGS 2000 assessment identified 76 "high priority" geologic provinces (based on the amount of oil and gas that has already been found to date) and 52 "frontier geologic provinces (regions for which there is geologic evidence that there may be very large amounts of oil and gas). These provinces are in essence the sedimentary basins that are considered to be world class in having the correct geological criteria to produce major petroleum accumulations. A conclusion of the GEODISC work on site assessment in Australia was that CO 2 storage will most likely work where major petroleum provinces occur. The sedimentary basins in Australia assessed to have the greatest potential for CO 2 storage were along the North West Shelf of Western Australia and the offshore part of the Gippsland Basin. These areas are the only regions from Australia that are recognized as being high priority in the USGS world petroleum assessment. Thus there is a strong correlation of the findings from these two assessments despite their different methodologies. Similar correlations exist with data emerging from other parts of the world, such as Canada and western Europe. By using the detailed findings in Australia and the knowledge and experience contained within these two primary datasets, extrapolations can be made as to which basins across the world are highly prospective for CO 2 storage potential ( world class basins), those that have low to high storage prospectivity, and those geological provinces that have no prospectivity for CO 2 storage. Limitations with the dataset, however, may affect the uncertainty of the interpretations. DATA LIMITATIONS Within the USGS dataset there are approximately 1000 polygons of geological features which can be classified into different geological provinces. Figure 1 shows the geological provinces of both sedimentary and nonsedimentary basins of the world, including where there are thick sedimentary basins underlying the ocean floor (i.e. the continental shelf). This map and the subsequent maps described below, are based on a worldwide dataset [4]. The dataset was compiled for the purposes of assessment of hydrocarbon potential, and in terms of CO 2 storage potential has limitations in the way that the information can be interpreted. For example the USGS dataset [4] gives little contextual information about the various geological provinces that are mapped, often only having local or derived names for each polygon, and many are historical in nature. In this exercise, the geological province name has been used as the primary key for subdivision, so that in some situations they are clearly not ideal for the purpose of subdividing the geological provinces into those that are prospective and non-prospective for CO 2 storage. For example, ambiguity exists in the use of qualifying words in province names that are largely geomorphologic features such as High, Low, Platform, Plateau, Ridge and Shelf, and others that are purely local geographic names with no geological qualifier such as basin, fold belt or shield. Similarly, although the term basin implies that a sedimentary basin is present, it does not indicate how highly deformed it might be, or whether the tectonic region is still active. The USGS dataset [4] give no detailed indication of the age or likely rock sequences that occur in each basin, which otherwise could be used as a further filter on the prospectivity of basins, e.g. Proterozoic versus Cainozoic, as the age of a basin can give an indication of the quality of potential reservoirs and seal integrity. However, given that it is not possible to generalize at a world scale that older basins will always have poor CO 2 storage potential when compared to younger basins, no such filtering has been attempted by use of additional datasets. These limiting features of the primary dataset imply that there is substantial uncertainty in some regions of the maps that are presented. However, for the purposes of this early stage of assessment, the approach adopted should be adequate, provided that the maps are treated as the starting point and not as representing the final result of attempts to find the best CO 2 storage locations for the world. A necessary step to further advance future world assessments would be to employ similar methodology to that utilized in Australia [3], at the country and basinal level. This is beyond the scope of this current world overview, therefore international forums should consider it as a priority research direction.
Figure 1: Simplified geological provinces of the world modified from USGS (2000) SUITABLE GEOLOGICAL PROVINCES Geological provinces of the world can be categorized into a variety of rock types and evolutionary histories, but those principally of interest to geological storage are sedimentary basins that have undergone only minor tectonic deformation and are at least 1000m thick with adequate reservoir/seal pairs to allow for the injection and trapping of CO 2. The major petroleum provinces of the world comprise sedimentary basins with adequate reservoir/seal pairs, viable organic rich source rocks that have generated hydrocarbons, and critically have had favorable timing in their evolution in terms of the formation of structural traps and charging of reservoirs within those traps with generated hydrocarbons. Sedimentary basins will contain clastic (sandstone and shale), carbonate (limestone) and coal lithologies, which all have some propensity to store and trap CO 2. Storage options will mostly rely upon deep saline reservoirs, depleted oil and gas fields and to a lesser extent deep coal seams. Detailed continent wide studies in Australia have shown that sedimentary basins that are major petroleum provinces will be ideal locations for geological storage of CO 2 [3]. Such basins have adequate reservoir / seal pairs, and suitable traps for hydrocarbons. Many of the minor petroleum provinces of the world are also anticipated to provide very favorable storage locations for CO 2. The critical difference between petroliferous basins and CO 2 storage basins is that the former must have had all their critical geological events occur in the correct sequence for petroleum to have been generated, trapped and stored, and thus require analysis of the dynamic history of the basin throughout their entire evolutionary history to predict their potential. For CO 2 storage basins however, drilling can identify whether adequate traps, seals and reservoirs occur now, and because timing is not an issue, then different methodologies for assessment can be utilized. Sedimentary basins with extensive coal deposits, that are potentially suitable for CO 2 storage, may or may not be geological provinces with significant petroleum accumulations. Some of the non-petroliferous sedimentary basins, that have failed to accumulate hydrocarbons due to poor relative timing of geological processes and events, will also be favorable for CO 2 storage, and in some instances will actually have higher potential than any of the petroleum bearing basins. Where the sedimentary basins have undergone significant deformation (e.g. fold belts), they will not be favorable for CO 2 storage due to thermal alteration that may have degraded the reservoir quality and due to structural complexities that normally occur in such provinces. Exceptions may occur, especially in relation to some coal deposits, as CO 2 will be injected via cleats (fractures) and trapped by adsorption onto the coal, rather than filling pore spaces. The remaining geological provinces of the world can generally be categorized as igneous and metamorphic provinces, commonly known as hard rock provinces, and these will not be favorable for CO 2 storage due to a lack of porosity and permeability in these rock types.
Based on the correlation between results for an assessment of the CO 2 storage potential of Australia [3] and Canada [5] with results within the USGS World Petroleum Assessment for Australia and Canada [4], it is possible to estimate which sedimentary basins of the world will have significant CO 2 storage potential. Figure 2 shows the geological provinces of the world categorized into provinces that are considered at a very simplistic level to comprise CO 2 storage potential that is either; Highly Prospective - those basins that are world class petroleum basins, and are high priority or frontier basins for the USGS World Petroleum Assessment [4], Prospective (low to high) - basins that are minor petroleum basins but not world class, as well as other sedimentary basins that have not been highly deformed, and Non-prospective - are highly deformed sedimentary basins and other geological provinces principally comprising fold belts, metamorphic and igneous rocks. Figure 2: High level estimate of the prospectivity of geological storage of CO 2 for sedimentary basins of the world Some prospective basins will have high potential for CO 2 storage whilst others will have low potential. Thus the highly prospective basins are a subset of the prospective basins. Determining the degree of suitability of any of these basins for CO 2 storage will be dependant on detailed work in each area. Some of the non-prospective provinces might have some boutique opportunities for CO 2 storage as alluded to above with coals in fold belts and perhaps in what is known as tight gas provinces. However, at this stage they would not be regarded as representing a conventional form of CO 2 storage, and most likely will not provide substantial volumes of potential storage capacity. Figure 3 shows all the basins which are prospective for geological storage potential overlain with present day tectonic activity, which has been defined by the epicentres of major earthquakes that occurred over the last 10 years with magnitudes of 5 or greater. As can be seen, many of these areas correlate with fold belts and hard rock provinces, although some sedimentary basins are intersected by and/or are adjacent to these tectonically active regions. Areas of active earthquakes are unlikely to be considered as desirable locations for large scale injection of CO 2 due to the complexity of structuring and the risk of reactivating faults during injection of CO 2. There are several petroleum provinces of the world that are tectonically active and have stored substantial volumes of hydrocarbons (e.g. California and parts of South-east Asia) and should not be automatically dismissed as unsuitable CO 2 storage locations. Each tectonically active province will have to be examined on its own geomechanical merits with an assessment of the likelihood of leakage up faults or reactivation during injection due to increased reservoir pressures.
Figure 3: Geographical relationship between recent earthquake epicentres and sedimentary basins prospective for geological storage of CO 2. SOURCE SINK MATCHING The international dataset of world emissions from the International Energy Agency (IEA) tabulates the location and magnitude of large stationary energy point sources [2]. This dataset is quite extensive, and although there are some inadequacies with it in terms of lacking precise geographic co-ordinates for some sites, it is still representative of the regions, especially when considered at the global level. By overlying this dataset in a GIS with the estimated CO 2 storage potential of the world sedimentary basins, as described above, it is possible to make some high level observations of the likely potential for source to sink matching for each continent (Fig 4). The dataset was interpreted by estimating the density and magnitude of emissions sources and their distance from prospective and highly prospective basins. Conclusions that can be made from this integrated dataset (Fig. 4) are that some geographic regions with large emissions profiles are either not located adjacent to or near sedimentary basins with high storage potential, or are adjacent to sedimentary basins that will require further detailed study to assess their full potential for CO 2 storage (prospective basins). This map does not address the relative capacity of any given sites to match the source, be it either a large emission supply or a small storage capacity. Neither does it address any of the technical uncertainties that could exist at any of the storage sites or cost implications of the emission source due to the nature of the emission plant or the purity of the emission sources. Where the nearest prospective basins are in offshore sedimentary basins, then information that will be beneficial for further assessment will include the level of petroleum exploration and production data that is available and whether there is pre-existing infrastructure that might become available, such as pipelines and platforms.
Figure 4: CO 2 emission sources locations (IEA GHG, 2002) and sedimentary basins prospective for geological storage of CO 2.
Figure 5 shows a graphical estimate of the source to sink matching potential for regions of the world and should be used as a guide to document the detail that can be ascertained when the maps are viewed for each region at a small scale. Each region with significant emissions are shown and their perceived likelihood of having storage sites located close to emission sources. The regions are ordered approximately in order of increasing emission volume and geographic density, with a visual estimate of the availability of potential opportunities for viable source to sink matching for the region, based upon placing a 300km radius around all point sources. No statistical analysis has been done, but such an approach is currently under consideration. All regions have a range of potential, but some clearly have more opportunities or challenges than others, and some have more than one population of opportunity types. Where low potential is indicated, the likelihood of distant sources is also included. Storage potential for CO 2 must be considered as a natural resource, just like oil, gas and coal, and as such it should be recognized that some regions will be richly endowed and others less so. Thus access to neighboring regions will be required if all regions are to have opportunities to geologically store their CO 2 emissions. Nearby <300 km Storage Potential Significant Moderate Low Distant Storage Potential 12 11 10 9 8 7 6 5 4 3 2 1 0 South America Africa Middle East Canada South-east Asia Australia Russia / Central Asia Indian Sub-continent Europe Japan USA China Figure 5: Table of the occurrence of nearby locations for geological storage of CO 2 relative to emissions sites and the abundance of such opportunities for each region. Where geographic source to sink mis-matches are predicted, there is a need to consider planning to locate new power plants closer to the sedimentary basins with high potential. Alternatively, where there are regions with high emissions due to a large number of point sources, they could plan for some form of industrial ecosystem or hub approach. These sources could then collectively transport CO 2 emissions longer distances and so by utilizing economies of scale, reduce the costs of transporting CO 2 larger distances to reach higher quality storage locations. Options also might exist to consider collection of CO 2 at a port facility and transport the CO 2 by ship tankers to an offshore sedimentary basin storage site, in much the same way as LNG and LPG are transported by ship around the world today. Figure 6 shows those emission sources specifically with high concentration (>95%) CO 2, and their proximity to prospective geological storage sites. This shows sites that could potentially be used in early demonstrations of CO 2 storage, comprising mostly ammonia and hydrogen producing plants that produce nearly pure CO 2. Particular opportunity clusters can be observed in China and to lesser extents in Europe and North America [6].
Figure 6: Geographical relationship between high concentration CO 2 emission sources and sedimentary basins with geological CO 2 storage potential FUTURE DIRECTIONS This assessment is based on identifying the regions of the world that may have some potential (prospectivity) for geological storage of CO 2, and their source to sink matching opportunities, but does not estimate storage capacity (volume). A few regions in the world have estimates of their storage capacity [7], but all have utilized a variety of methodologies. Such inconsistent approaches make comparative assessment of world storage capacity problematic. Future research is going to focus on whether it is possible to extend and implement a similar approach as the prospectivity assessment used here, and make a high level world overview of storage capacity. Such values, if found to be robust and consistent, will be fundamental to future matching of source volume to storage capacity as well as to more accurately constrain economic modeling of the future impact of CO 2 sequestration [8]. CONCLUSIONS By combining datasets from world wide assessments for hydrocarbon potential with more limited country wide assessments of CO 2 storage potential, it is possible to make a global prediction, at a first pass level, of the regional prospectivity for geological storage of CO 2. Some regions have significant prospectivity with good source to sink matches, whilst others are less well endowed in their local region and might require longer transport distances and higher costs. Those that do not have favorable outcomes due to geographic mis-matches of source and sink may need to plan for the future and aim to reduce costs by locating new emission sites closer to storage sites, or by potentially considering hub or industrial ecosystem approaches, or considering development of ship tanker technologies. Hubs which centralize the collection and transport of CO 2 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. As some parts of some regions will have challenges associated with their source to sink matches, access to the development of centralized storage locations for a region could become a critical component to any future involving large scale uptake of geological storage of CO 2 technology. REFERENCES 1. Bradshaw, J., Allinson, G., Bradshaw, B.E., Nguyen, V., Rigg, A.J., Spencer, L., and Wilson, P., 2004: Australia s CO 2 geological storage potential and matching of emissions sources to potential sinks. Energy 29 1623-1631
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