The storage of CO2 in porous, saline formations naturally results in the displacement of ambient pore waters. In large, permeable formations this can be readily accomplished, but in smaller, or less permeable formations the pressure needed to displace the pore fluid may be significant. To improve our ability to predict the volume of CO2 which can be safely stored, and to predict the displacement of pore fluids and the buildup of ambient pressure we are modelling the propagation of pressure throughout the reservoir. This signal, of enhanced pressure, drives small deformations which can be observed in minute ground motion detectable over large distances from satellite imagery. By constructing reduced models to explain this surface ground deformation in current storage sites we can understand something of the distribution of pressure over time within storage reservoirs.
For the storage potential of the UK North Sea to be realised, CO2 will have to be stored over a range of reservoir types, from older lithified and less permeable rocks to much younger more permeable sites. Research will focus on understanding transient pressure response, pressure propagation, induced strain and post-injection pressure decay in aquifers of varying degrees of cementation, rigidity, and edimentological and structural complexity via multi-scale numerical and analytical modelling. This will examine the impact of small-scale rock heterogeneity, the effect of compartmentalisation by faults and their damage zones, and by stratigraphical and diagenetic complexity, on the amount of CO2 that can be stored in each reservoir type. Data will be obtained from a number of reservoirs covering the range of length scales that control the pressure response both proximally and distally. Data scale-up from these reservoirs will include core-size pore distribution, outcrop, 3D seismics and extended period satellite surface elevation records. The work will focus on faults and fault damage zones (e.g. deformation bands) as the flow behaviour of these to different fluids is not well understood. The bulk flow properties of these features will be established, so they can be properly incorporated into storage assessments and storage security evaluations. A key outcome of the work will be the ability to upscale the results from core/outcrop scale to reservoir scale through the use of multi-scale flow models, analytical models and umerical upscaling tools. Results will interface with the process models developed in WP B2. Modelling will be calibrated by real datasets from large-scale production and storage including: injection pressures; long-term pressure recharge; dynamic well tests; time-lapse seismics; syn and post-injection InSAR surface elevations. It will utilise findings from the DiSECCS project (EP/K035878/1) which has developed new seismic tools for identifying and characterising pressure changes in injection reservoirs. The work will result in improved understanding of pressure build-up, propagation and decay in faulted and heterogeneous reservoirs.