Linking outcrop analogue with flow simulation to reduce uncertainty in sub-surface carbon capture and storage: an example from the Sherwood Sandstone Group of the Wessex Basin, UK

Abstract

Modelling the behaviour of carbon dioxide (CO2) injected into sub-surface reservoirs as part of carbon capture and storage (CCS) strategies is often performed using models that incorporate very limited geological detail, particularly at the subseismic (metre to decametre) scale. Those modelling studies that incorporate varying degrees of geological realism show the inherent risks and uncertainties that can result from neglecting heterogeneity and reservoir–caprock topography along the migration path of an injected CO2 plume. A key problem is that detailed geological data are often not available for the relatively deep saline aquifers that are an important target for CCS. Deep saline aquifers fall between the relatively data-rich environments of shallow freshwater aquifers and hydrocarbon reservoirs and it is in these settings that outcrop analogues may play an important part in reducing the risks and uncertainties associated with CCS. This study uses an example from the Sherwood Sandstone Group (Otter Sandstone Formation) of the Wessex Basin to show how an outcrop study can impart a much greater understanding of heterogeneity in critical reservoir–caprock zones. Here the transition from the Sherwood Sandstone Group (fluvial sandstone reservoir) to the Mercia Mudstone Group (playa lacustrine mudstone seal) is not simple, but includes a major change in fluvial style that introduces considerable heterogeneity at the top of the reservoir. The study shows how laser-scanned outcrop can be used to rapidly construct static geological models that are taken through to flow simulations. In combination, the use of appropriate outcrop analogues and flow modelling can reduce the risks and uncertainties associated with CCS.

Using core and outcrop analogues to predict flow pathways in the subsurface: examples from the Triassic sandstones of north Cheshire, UK

“…Recent numerical modelling studies (e.g. Newell and Shariatipour, 2016) have used cell sizes that are too large to account for the heterogeneities identified in this study; however with future improvements in computing capabilities, it will be im-portant to model these sub-seismic scale heterogeneities to fully understand the impact they have on flow in these units.…”

Evolving stratigraphy of a Middle Triassic fluvial‐dominated sheet sandstone: The Otter Sandstone Formation of the Wessex Basin (UK)

“…The Pennington Point Member has a sharp or erosive contact with the underlying amalgamated sheet sandstones of the Chiselbury Bay Member (Figure d). Localized scours on the basal erosion surface are variably infilled with sandstone, mudstone, or a heterolithic combination of both (Newell & Shariatipour, ). The upper contact of the Pennington Point Member with the Mercia Mudstone Group is gradational, with a progressive decrease in sandstone bed thickness and an increase in the proportion of mudstone.…”

“…The Pennington Point Member is made from a number of distinct lithofacies: Isolated point bar deposits: These are best observed in the cliffs at High Peak near Big Picket Rock where they occur immediately below the Mercia Mudstone Group on cliff faces that cut the deposits at a high angle relative to palaeoflow direction. Although inaccessible, they have been mapped using terrestrial laser scan data (Figure ; Newell & Shariatipour, ). The point bar deposits are up to 6 m thick and comprise a lower bar core composed of trough cross‐bedded sandstone that passes upwards and laterally into a series of inclined sandstone and mudstone bed couplets that downlap onto a relatively horizontal basal erosion surface. Splay sandstones: These are represented by bundles of relatively thin (<1 m) tabular or lenticular sandstone beds interbedded with mudstone (Figure ).…”

Characterizing flow pathways in a sandstone aquifer: Tectonic vs sedimentary heterogeneities

“…This work investigates the sandstone aquifer of the Triassic St Bees Sandstone Formation, which represents the basal part of the Sherwood Sandstone Groupthe second most important UK aquifer in terms of the amount of groundwater abstracted (Allen et al, 1997;Binley et al, 2002;Smedley et al, 2002). The Sherwood Sandstone Group has been the object of recent studies of sedimentary heterogeneities (e.g., Medici et al, 2015;Newell et al, 2016;Wakefield et al, 2015).…”