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

Abstract

Abstract. Borehole core provides detailed vertical data which is used to interpret subsurface sand body architectures, but assumptions are made on the relationship between the lateral and vertical thickness, and the interconnectivity of units. The sedimentological complexity of the Sherwood Sandstone Group succession in this area, passing between aeolian and fluvial packages creates local- to regional-scale heterogeneities which will impact flow pathways within the rockmass. Measured thickness in boreholes might represent an architectural element's true maximum thickness or more likely, a partial thickness as a result of incision by overlying facies types or as a result of the borehole sitting towards the margins of individual elements (e.g. tapering margin of channel elements). Length and thickness data were measured from a suite of primary core data and secondary published outcrop studies in north-west England. The addition of outcrop studies in combination with the borehole data provides a dataset from which the likely lateral extent of the architectural frameworks within the Triassic sandstones can be extrapolated. The interpreted high resolution sub-seismic architecture contributes to an increased understanding of flow pathways and the effect these may have on groundwater as well as sustainable energy technologies such as low-temperature geothermal aquifers, carbon storage and energy storage.

Use of Outcrop as Substitute for Subsurface Shale: Current Understanding of Similarities, Discrepancies, and Associated Challenges

“…The similarity between the properties of the outcrop and the equivalent sandstone and carbonate subsurface formation samples exists mainly in petrophysical properties, of which the mineralogy is most often matched. ,, However, limited studies have been performed to compare the properties of subsurface shale reservoir formations with their surface outcrops. Mineralogy of organic shales and mudstones is a key control factor of reservoir quality and completion in the development phase.…”

“…The detailed outcrop studies enable us to add significant fidelity to our understanding of the geological characteristics of the producible shale formations. Outcrop characterization in both vertical and lateral extents is used to construct flow models that depict flow in the units at the subseismic scale . The properties directly measured on the outcrop analogs can provide insight into the behavior of subsurface sections and help in minimizing the uncertainties while designing the characterization models of the reservoir.…”