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

Giacomo Medici,L. Jared West,Nigel P. Mountney,Michael Welch

doi:10.1007/s10040-019-02035-7

Giacomo Medici, L. Jared West + Show 2 more

Open Access

https://doi.org/10.1007/s10040-019-02035-7

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Abstract

Fluvio-aeolian sedimentary successions host groundwater aquifers at shallow depths (<~0.15 km), which overlie geothermal and shale-gas reservoirs, and nuclear waste repositories at intermediate depths (~0.15–2.0 km). Additionally, such deposits represent petroleum reservoirs at greater depths (~2.0–4.0 km). The need to improve conceptual understanding of the hydraulic behaviour of fluvial-aeolian sandstone successions over a large depth interval (~0–4 km) is important for socio-economic reasons. Thus, the hydraulic properties of the Triassic Sherwood Sandstone aquifer in the UK have been reviewed and compared to similar fluvio-aeolian successions. The ratio between well-scale and core-plug-scale permeability (Kwell-test/Kcore-plug) acts as a proxy for the relative importance of fracture versus intergranular flow. This ratio (which typically varies from ~2 to 100) indicates significant contribution of fractures to flow at relatively shallow depths (<~0.15 km). Here, permeability development is controlled by dissolution of calcite-dolomite in correspondence of fractures. The observed ratio (Kwell-test/Kcore-plug) decreases with depth, approaching unity, indicating that intergranular flow dominates at ~1 km depth. At depths ≥ ~1 km, dissolution of carbonate cement by rock alteration due to groundwater flow is absent and fractures are closed. Aeolian and fluvial deposits behave differently in proximity to normal faults in the Sherwood Sandstone aquifer. Deformation bands in aeolian dune deposits strongly compartmentalize this aquifer. The hydro-structural properties of fluvio-aeolian deposits are also controlled by mineralogy in fault zones. A relative abundance of quartz vs. feldspar and clays in aeolian sandstones favours development of low-permeability deformation bands.

Highlights

Fluvial and aeolian deposits commonly form thick sedimentary successions (>1 km) in basins for which accommodation was generated in response to compressional, strike-slip and extensional tectonics, as well as thermal subsidence (Bosellini 1989; Waugh 1973)—for example, continental deposits of fluvial and aeolian origin represent a part of foreland
Geothermal production wells are planned in correspondence of extensional faults with large damage zones to exploit the property of maximum permeability parallel to the fracture planes (Loveless et al 2014; Moreno et al 2018)
This article provides valuable insights for management of deep (~0.15–2.0 km) siliciclastic fluvio-aeolian aquifers which are the object of renewed attention due to the growing interest in geothermal energy and protection from escape of contaminants from deep hydraulic fracturing of shale gas reservoirs, and in connection with deep nuclear waste repositories

Summary

Introduction

Siliciclastic deposits of continental origin can serve as important hosts for groundwater resources, and geothermal and Hydrogeol J (2019) 27:2835–2855 hydrocarbon reservoirs (Aldinucci et al 2008; Colombera et al 2019; McKie et al 2010; Tellam and Barker 2006; Yuan et al 2015). At depths up to ~2,000 mBGL, siliciclastic aquifers of fluvial and aeolian affinity overlie targets for production of shale gas in NW Europe (Loveless et al 2018). Faults in sandstone influence the potential for upwards transport of contaminants from both nuclear waste repositories and hydraulically fractured reservoirs of shale gas (Bense et al 2013, 2016; Cai and Ofterdinger 2014; Flewelling and Sharma 2014). Geothermal production wells are planned in correspondence of extensional faults with large damage zones to exploit the property of maximum permeability parallel to the fracture planes (Loveless et al 2014; Moreno et al 2018)

Objectives

Conclusion