Sedimentary flow heterogeneities in the Triassic U.K. Sherwood Sandstone Group: Insights for hydrocarbon exploration

Abstract

Fluvial and aeolian sedimentary successions host important hydrocarbon resources as well as major groundwater aquifers. This review of the lithological characteristics of Triassic fluvio‐aeolian successions of the Sherwood Sandstone Group (United Kingdom) demonstrates how distance from a fluvial sediment source and rate of rift‐related tectonic subsidence play important roles in governing reservoir quality in continental successions. Increasing distance from the fluvial sediment source area results in increased porosity and permeability in deposits of mixed fluvial and aeolian reservoir successions that accumulated in arid and semiarid settings. Indeed, successions of the U.K. Sherwood Sandstone Group reveal an increase in the proportion of highly permeable deposits of aeolian origin with increasing distance from the principal uplands, represented by the Armorican Massif in northern France, which formed the main source for delivery of fluvial sediment to a series of rift basins. A progressive reduction in the discharge of fluvial systems entering and passing through a series of interlinked rift basins encouraged aeolian accumulation in more distal basins. Extensional tectonics enabled preservation of highly permeable aeolian facies in basins subject to high rates (≳100 m/Myr) of tectonic subsidence by rapidly placing such deposits below the water table. However, successions exclusively characterized by fluvial lithofacies record decreases in both porosity and permeability with increasing distance (~250–750 km) from the sediment source due to the coupling of porosity reduction and increasing clay content.

Permeability of rock discontinuities and faults in the Triassic Sherwood Sandstone Group (UK): insights for management of fluvio-aeolian aquifers worldwide

“…Morpho-structural highs in Great Britain served as a major source of sediment for fluvial systems. The principal sediment source of these fluvial systems of Triassic age is represented by the Armorican Massif in northern France (McKie and Williams 2009;Medici et al 2019b). Extensional tectonics continued after the Permo-Triassic climax and continued to affect basins in England throughout much of the Jurassic and Cretaceous (Chadwick and Evans 1995;Chadwick 1997).…”

“…The progressive reduction in the discharge of this Triassic system entering a series of interlinked rift basins (see Fig. 1b,c) may have encouraged aeolian sedimentation, accumulation and preservation in the northern, more distal, basins (Medici et al 2019b).…”

“…However, lithofacies associations of aeolian origin (LA3) are characterized by cross-bedded dune deposits, fine-grained sandstones of damp interdune origin and siltstones of wet interdune origin (Mountney and Thompson 2002). Note that detail of lithostratigraphy, lithofacies arrangements and link with depositional palaeoenvironment of the fluvio-aeolian deposits of the Sherwood Sandstone Group can be found in McKie and Williams (2009) and Medici et al (2019b).…”

“…However, this work reviews the multi-scale properties of both deposits of aeolian and fluvial origin buried up tõ 4 km depth. Previous reviews on the multi-scale properties of fluvial and aeolian successions focus at depths <~150 mBGL (Allen et al 1997;Tellam and Barker 2006), or on the effect on flow of the sedimentary heterogeneities to guide hydrocarbon exploration on optimization of oil recovery (Medici et al 2019b). The petrohydraulic properties of the Triassic fluvio-aeolian deposits of Great Britain have been reviewed by Medici et al (2019b) in relation to sedimentological factors including reconstructed palaeoclimate and depositional palaeoenvironment.…”

Three‐dimensional forward stratigraphic modelling of the sedimentary architecture of meandering‐river successions in evolving half‐graben rift basins

“…Assessing and predicting lithological complexity in the fill of rift basins is important for two principal reasons: (a) it enables models to be developed whereby the sedimentary record can be used to reconstruct histories of basin evolution and to help assess the impacts of tectonic control on sedimentation, (b) from an applied standpoint, the deposits of fluvial successions in rift basins form major oil and gas reservoirs (Corbett, Hamdi, & Gurav, 2012;Hamdi, Ruelland, Bergey, & Corbett, 2014;Medici, West, & Mountney, 2018b), serve as important groundwater aquifers (Lockwood, 2001;Medici, West, & Mountney, 2016;Tellam & Barker, 2006), and act as potential sites for long-term carbon sequestration (Bachu, 2000) and for the underground storage of radioactive waste (Bath et al, 2006;Medici, West, & Mountney, 2018a). Point-bar deposits of meandering rivers are of particular importance in applied geology due to their economic potential as major hydrocarbon reservoirs (Jolley, Fisher, & Ainsworth, 2010;Larue & Hovadik, 2006).…”