Geological Survey of Denmark and Greenland Bulletin 33, 2015, 85-88 85© 2015 GEUS. Geological Survey of Denmark and Greenland Bulletin 33, 85–88. Open access: www.geus.dk/publications/bull Reserves and resources for CO2 storage in Europe: the CO2StoP project Niels Poulsen, Andrei Bocin-Dumitriu, Sam Holloway, Karen Kirk, Filip Neele and Nichola Smith Th e challenge of climate change demands reduction in global CO2 emissions. In order to fi ght global warming many coun- tries are looking at technological solutions to keep the release of CO2 into the atmosphere under control. One of the most promising techniques is carbon dioxide capture and storage (CCS), also known as CO2 geological storage. CCS can re- duce the world’s total CO2 release by about one quarter by 2050 (IEA 2008, 2013; Metz et al. 2005). CCS usually in- volves a series of steps: (1) separation of the CO2 from the gases produced by large power plants or other point sources, (2) compression of the CO2 into supercritical fl uid, (3) trans- portation to a storage location and (4) injecting it into deep underground geological formations. CO2StoP is an acronym for the CO2 Storage Potential in Europe project. Th e CO2StoP project which started in Janu- ary 2012 and ended in October 2014 included data from 27 countries (Fig. 1). Th e data necessary to assess potential loca- tions of CO2 storage resources are found in a database set up in the project. A data analysis system was developed to analyse the com- plex data in the database, as well as a geographical informa- tion system (GIS) that can display the location of potential geological storage formations, individual units of assessment within the formations and any further subdivisions (daugh- ter units, such as hydrocarbon reservoirs or potential struc- tural traps in saline aquifers). Finally, formulae have been developed to calculate the storage resources. Th e database is housed at the Joint Research Centre, the European Commis- sion in Petten, the Netherlands. Background and methods CO2 storage resource assessment A resource can be defi ned as anything potentially available and useful to man. Th e pore space in deeply buried reservoir rocks that can trap CO2 is a resource that can be used for CO2 storage. It is of utmost importance to be aware that the mere presence of a resource does not indicate that any part of it can be economically exploited, now or in the future. A reserve can be defi ned as that part of a resource that is available to be economically exploited now using currently available technology. Th us, in order to move from a resource estimate to a reserve estimate, a whole series of technical, economic, legal and socio-economic criteria must be applied. Th ese criteria will then identify the fraction of the resource that can actually be economically exploited in a particular jurisdiction area, using available technology. Consequently, a very high level of technical assessment is required to demonstrate the existence of a CO2 storage reserve, and in most cases these kinds of resources are only available within a demonstration or commercial storage pro- ject. For these reasons, it was impossible to defi ne any CO2 storage reserves in the present project. 16°W 16°E 32°E 48°E 56°E 64°E 50°N 42°N 0 16°E0° 58°N 50°N 500 km 42°N 66°N CO 2 StoP project covered by Geological surveys Universities National institutes Geol. survey/university Not in CO 2 StoP Latvia covered by the Estonian-Latvian transboundary project 8°E Fig. 1. Twenty-seven countries participated in the CO2StoP project. Lat- via was covered by the Estonian–Latvian border project. The following member states of the European Union participated: Austria, Belgium, Bulgaria, Croatia, Czech Republic, Denmark, Estonia, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, the Netherlands, Po- land, Portugal, Romania, Slovakia, Slovenia, Spain and UK and the fol- lowing non-member states: Macedonia, Norway, Serbia and Switzerland. 8686 Storage mechanisms CO2 can be retained in reservoir rocks by a number of mechanisms: (1) structural and stratigraphic trapping, in which CO2 is retained by impermeable barriers, (2) residual trapping, in which free phase CO2 is trapped by capillary forces in pore spaces, (3) dissolution of CO2 into pore fl uids, (4) precipitation of CO2 into minerals and (5) adsorption onto shale or coal layers. Only the fi rst two of these mecha- nisms are signifi cant within a CO2 storage project’s time frame of 10 to 50 years; the other mechanisms take much longer (van der Meer & van Wees 2006). Th erefore, most previous studies of CO2 storage resources (e.g. USGS Assessment; DOE Storage Atlases; Norwegian Assessment; IEA Best Practices document) focussed on de- termining the amount of CO2 that can be retained in con- ventional reservoir rocks as a dense fl uid in the fl uid-fi lled pore spaces between the grains that make up the matrix of the rock and in fl uid-fi lled fractures. Moreover, the vast ma- jority of the CO2 will be trapped either in structural and stratigraphic traps or by capillary forces as a residual satura- tion (Bachu et al. 2007). Constraints on CO2 storage capacity Each jurisdiction area contains a given amount of pore space within its subsurface. Th e total resource of pore space that is potentially available for CO2 storage is that part which can be fi lled with, and will retain, injected CO2. Geology and physics dictate that this will be far less than the available total pore space. Th ese limitations mean that only a small fraction of the total resource of pore space can be fi lled with CO2. It is possible to defi ne a common method that can be used to estimate the fraction of the total pore space resource that can be used for storage (Brennan 2014). If appropriate CO2 densities at reservoir conditions are applied to this vol- ume, this allows estimation of the theoretical CO2 storage resource. In practice, only a fraction of the theoretical CO2 storage resource in any given jurisdiction area can actually be utilised – for a variety of technical, economic, legal and social rea- sons. In the CO2StoP project, the pore space in a jurisdiction area is subdivided into reservoir formations. Th ese are map- pable bodies of rock which display mainly suffi cient porosity and permeability. Each reservoir formation contains one or more storage units. A storage unit is defi ned as a part of a res- ervoir formation that is found at depths greater than 800 m and which is covered by an eff ective cap rock. Th ese units are potential CO2 storage units and they form the basis for the CO2 storage assessments made in the CO2StoP project. Each storage unit may contain one or more daughter units. Daughter units are defi ned as structural or stratigraphic traps which have the potential to immobilise CO2 within them, e.g. structural domes or proven oil and gas fi elds. Th e storage potential of daughter units can be estimated sepa- rately in CO2StoP. The CO2StoP method Th e CO2StoP project has established a database, a geographi- cal information system (GIS; ESRI’s ArcGIS 10) and a calcu- lation engine that can provide probabilistic estimates of CO2 storage capacities. Th e Data Analysis & Interrogation Tool is a combination of Microsoft Access (Data Interrogation tool), and Excel (StoreFit tool) with external code (linked to Excel) to perform injection rate calculations. Calculations carried out with the Database Analysis & Interrogation Tool include: storage capacity, injection rates and stochastic analy- ses of the storage capacity and injection rates (Fig. 2). Th e work to establish internationally recognised stand- ards for capacity assessments was initiated by the Carbon Sequestration Leadership Forum (CSLF) about a year before the start of the European Union GeoCapacity project, and a CSLF Task Force has been active since. Th e paper ‘Estima- tion of CO2 storage capacity in geological media – phase 2’ by Bachu et al. (2007) published by the CSLF presents com- prehensive defi nitions, concepts and methods to be used in estimating CO2 storage capacity. As in the EU GeoCapacity, the CO2StoP method com- plies with the CSLF recommendations. Th e methods and calculations for determining the fractions of the resource, used in the CO2StoP project, also align with the recent In- ternational Energy Agency proposals for harmonising CO2 storage capacity estimation methods (Heidug 2013). Th e CO2StoP method estimates the TASR (see below) and the storage resource in structural and stratigraphic traps, which have later been divided into two subsets: hydrocarbon fi elds and aquifer daughter units. The technically accessible CO2 storage resource (TASR) Th e CO2StoP calculation engine can produce a resource es- timate that is similar to the technically accessible CO2 stor- age resource (TASR) estimated by the US Geological Survey (Brennan et al. 2010; Blondes et al. 2013; U.S. Geological Survey Geologic Carbon Dioxide Storage Resources Assess- ment Team 2013). Th is is the fraction of the theoretical stor- age resource that can be accessed using all currently available technologies regardless of cost. Th e International Energy Agency recommended that the fi rst step in all CO2 storage resource estimates should be to assess the TASR (Heidug 2013). 87 Th e CO2StoP estimate diff ers in one main respect from the TASR estimated by the U.S. Geological Survey method, namely that CO2StoP adds the storage capacity of hydrocar- bon fi elds to that of the saline aquifers. Th is has to be done because the pore volume of the hydrocarbon fi elds is not provided in the project’s database, so it cannot be subtracted from the pore volume of the storage units before their stor- age capacity is estimated. Th ere are other minor diff erences in the constraints and assumptions; nevertheless, the two methods produce results that are suffi ciently similar to allow them to be compared. Results Th e assessment of the various fractions of the CO2 geological storage resource performed in the CO2StoP project is cur- rently only at a provisional level. Unfortunately, large diff er- ences exist between the types and quality of data available for each country, and the extent to which the data can be made public also varies widely. Some countries only have data avail- able from traps for buoyant fl uids, where the TASR will be low not taking into account any potential for storage outside such traps by residual saturation. Some countries have included aquifer formation data; here the TASR calculation will be more meaningful. In the great majority of countries, uncer- tainties related to lack of reservoir parameter data also re- main. Th e acquisition of such data will potentially require a sustained campaign of geological mapping and characterisa- tion of storage capacity, or at least signifi cantly more time and fi nancial resources to assemble and enter all available data. Th ese factors limit the results obtained from the CO2StoP project and it is recommended that further resources are made available for improving the results. In a European context, the technically accessible CO2 storage resource (TASR) or theoretical storage resource should only be used for extra-European international re- source comparisons because it is clear that the TASR is sev- eral times greater than the practical CO2 storage capacity. Consequently quoting the TASR can be misleading, giving false impressions of capacity if a critical distinction between resource and reserve estimates is not made. CO2StoP GIS Data analysis tool CO2STOP DATA INTERROGATION SYSTEM CO2 injection capacity Data entry system View, filter and export data Import results DSF: Deep Saline Formation DGF: Depleted Gas Field FILL DATA CALCULA- TIONS & DATA CHOICES PRIMARY INPUT OUTPUT DATA StoreFit Areas studied for the CO2SToP GIS S to ra ge i d C ap ac it y d at ab as e (M t) F ie ld e x e n t (k m 2 ) T h ic k n e ss (m ) S T O R A G E U N IT T R A P T R A P N A M E C A S E N A M E C A S E n o MESSAGES input file output file Countries studied Countries not par- ticipating in CO 2 StoP project Aquifer daughter units Hydrocarbon daughter units Storage units Formations length name 62 89 Fig. 2. Schematic representation of the Database Analysis & Interrogation Tool, showing the GIS and the StoreFit Monte Carlo analysis tool. Arrows indicate data exchange between the separate elements of the tool. The map shows the reported resources in the CO2StoP project. 8888 Conclusions Th e calculations of CO2 storage locations throughout Europe made by the CO2StoP project database paint a broad picture, but also identify the gaps in our knowledge. Th ese gaps must be fi lled with further data entry and, potentially, new geological studies, seismic surveys and drilling must be undertaken to make more precise data available. A common European legislation allowing equal access to proprietary subsurface information would be benefi cial for this purpose. It is critically important to understand the assumptions that lie behind the storage capacity estimates. Th ese are espe- cially relevant for saline formations, the capacities of which were derived without taking regulatory or economic limita- tions into account. Th e CO2StoP method has made signifi cant progress to- wards establishing probabilistic estimates of the CO2 storage resource in Europe in a way that will allow comparisons with other regions of the world, and which will also be useful to policy makers. However, the partial data entry into the pro- ject database means that the current project only marks the beginning of the process of resource estimation and certainly not the end. Acknowledgements Th e CO2StoP project was funded by the European Commission (project no ENER/C1/154-2011-SI2.611598). We express our sincere thanks to Andrei Bocin-Dumitriu (EC Joint Research Centre) and to Kai Tullius, Øivind Vessia, Rakel Hunstad and Ilinca Balan from the European Com- mission, Directorate General for Energ y for their help and support with this project and to this report and the other deliverables. We also thank the CO2StoP project partners for their contributions of country specifi c information. Legal notice Th is publication is based on a project for the European Commission; how- ever it refl ects the views only of the authors, and the commission cannot be held responsible for any use which may be made of the information con- tained therein. References Bachu, S., Bonijoly, D., Bradshaw, J., Burruss, R., Christensen, N.P. Hollo- way, S. & Mathiassen, O.M. 2007: Estimation of CO2 storage capacity in geological media – phase 2. Work under the auspices of the Carbon Sequestration Leadership Forum (www.cslforum.org). Final report from the task force for review and identifi cation of standards for CO2 storage capacity estimation, 43 pp. Washington: Carbon Sequestration Leadership Forum. Blondes, M.S. et al. 2013: National assessment of geologic carbon diox- ide storage resources –methodolog y implementation. 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U.S. Geological Survey Geologic Carbon Dioxide Storage Resources Assessment Team 2013: National assessment of geologic carbon dioxide storage resources – results (ver. 1.1, September 2013). U.S. Geological Survey Circular 1386, 41 pp. Van der Meer, L.G.H. & van Wees, J.D. 2006: Eff ects of CO2 solubility on the long-term fate of CO2 sequestered in a saline aquifer. Th e Leading Edge 25, 1276–1280. Authors’ addresses N.P., Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. E-mail: nep@geus.dk A.B.-D., European Commission, DG JRC, Institute for Energy and Transport, Energy Technology Policy Outlook Unit, Westerduinweg 3, 1755 LE Petten, The Netherlands. S.H. & K.K., British Geological Survey (BGS), Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG, UK. F.N., TNO, Earth Environment and Life Sciences, Postal address: P.O. Box 80015, 3508 TA Utrecht, The Netherlands. N.S., British Geological Survey, Murchison House, West Mains Road, Edinburgh, EH9 3LA, UK.