We use a combination of experimental design, sketch-based reservoir modelling and flow diagnostics to rapidly screen the impact of sedimentological heterogeneities that constitute baffles and barriers on CO ₂ migration in depleted hydrocarbon reservoirs and saline aquifers of the Sherwood Sandstone Group and Bunter Sandstone Formation, UK. These storage units consist of fluvial sandstones with subordinate aeolian sand-stones, floodplain and sabkha heteroliths and lacustrine mudstones. The predominant control on effective hor-izontal permeability is the lateral continuity of aeolian-sandstone intervals. Effective vertical permeability is controlled by the lateral extent, thickness and abundance of lacustrine-mudstone layers and aeolian-sandstone layers, and the mean lateral extent and mean vertical spacing of carbonate-cemented basal channel lags in fluvial facies-association layers. The baffling effect on CO ₂ migration and retention is approximated by the pore vol-ume injected at breakthrough time, which is controlled largely by three heterogeneities, in order of decreasing impact: (1) the lateral continuity of aeolian-sandstone intervals; (2) the lateral extent of lacustrine-mudstone lay-ers; and (3) the thickness and abundance of fluvial-sandstone, aeolian-sandstone, floodplain-and-sabkha-heter-olith and lacustrine-mudstone layers. Future effort should be focused on characterizing these three heterogeneities as a precursor for later capillary, dissolution and mineral trapping.

Sketch-based modelling with flow diagnostics provides a prototyping approach to quickly build geomodels and generate quantitative results to evaluate volumetrics and flow behaviour. This approach allows users to rapidly test the sensitivity of model outputs to different geological concepts and uncertain parameters, and informs selection of geological concepts, scales and resolutions to be investigated in more detailed models. Rapid Reservoir Modelling (RRM) is a sketch-based modelling tool with an intuitive interface that allows users to rapidly sketch geological models in 3D. Geological models that capture the essence of heterogeneity of interest and related uncertainty can be created within minutes. Flow diagnostics then instantly computes key indicators of predicted flow and storage behaviour within seconds. Here we apply the prototyping approach to three aspects of geoenergy modelling: (1) scenario screening to identify heterogeneities with the most impact; (2) use of mini-models and hierarchical models to derive effective properties; and (3) training of geoscientists and engineers to investigate the impact of geological interpretations on storage volumes and connectivity. Geomodels addressing all three aspects are constructed and analysed quickly, using simple, geologically intuitive workflows that do not require prior geomodelling expertise.