Static and Dynamic Estimates of CO2 Storage Capacity in Two Saline Formations in the UK
- Min Jin (Heriot Watt University) | Gillian E. Pickup (Heriot Watt University) | Eric James Mackay (Heriot Watt University) | Adrian Christopher Todd (Heriot Watt University) | Alison Monaghan (British Geological Survey) | Mark Naylor
- Document ID
- Society of Petroleum Engineers
- SPE EUROPEC/EAGE Annual Conference and Exhibition, 14-17 June, Barcelona, Spain
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 5.1.5 Geologic Modeling, 6.5.3 Waste Management, 5.1.1 Exploration, Development, Structural Geology, 4.3.4 Scale, 3 Production and Well Operations, 5.4.2 Gas Injection Methods, 5.9.2 Geothermal Resources, 6.5.1 Air Emissions, 5.5 Reservoir Simulation, 5.10.1 CO2 Capture and Sequestration, 5.4 Enhanced Recovery
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Estimation of CO2 storage capacity is a key step in the appraisal of CO2 storage sites. Different calculation methods may lead to widely diverging values. The compressibility method is a commonly used static method for estimating storage capacity of saline aquifers: it is simple, easy to use and requires a minimum of input data. Alternatively, a numerical reservoir simulation provides a dynamic method which includes Darcy flow calculations. More input data are required for dynamic simulation, and it is more computationally intensive, but it takes into account migration pathways and dissolution effects, so is generally more accurate and more useful. For example, the CO2 migration plume may be used to identify appropriate monitoring techniques.
Two typical saline aquifer storage sites were analysed using both static and dynamic methods. One site has a comparatively simple geology, while the other has a more complex geology. For each site both static and dynamic capacity calculations were performed. CO2 injection for 15 years was followed by a closure period lasting thousands of years. The proportion of dissolved CO2 and the proportion immobilised by pore scale trapping were calculated.
The results of both geological systems show that the migration of CO2 is strongly influenced by the local topography of the upper surface of the aquifer formation. The calculated storage efficiency for the first site varied between 0.5% and 1% of total pore volume, depending on whether the systems boundaries were considered open or closed. Simulation of the deeper, more complex geological system gave storage capacities as high as 2.75%.
This work is part of the CASSEM (CO2 Aquifer Storage Site Evaluation and Monitoring) integrated study to derive methodologies for assessment of CO2 storage in saline formations. Although, static estimates are useful for initial assessment, we demonstrate the value of performing dynamic storage calculations, and the opportunities to identify mechanisms for optimising the storage capacity.
Keywords: CO2, Storage Capacity, Saline Aquifer
Carbon Capture and Storage (CCS) is considered to be an important means of reducing greenhouse gas emissions. CO2 may be stored in depleted oil and gas fields, deep saline aquifers or unmineable coal seams. Of these options, deep saline aquifers have the greatest storage potential both world-wide (IPCC, 2005) and in the UK (SCCS, 2009). However, there is much uncertainty in the size and structure of aquifers compared to hydrocarbon reservoirs and estimation of CO2 storage capacity is therefore a key step in the appraisal of CO2 storage sites. This procedure is, however, complex (Bachu et al., 2007a; van der Meer and Egberts, 2008) and the results of estimations at regional or global level are widely scattered (Bachu et al., 2007a) due to different assumptions and lack of data. One of the most important assumptions is the boundary condition, i.e. whether the aquifer is closed (finite) or open (infinite), not only at the site scale but also at the basin or region scale.
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