The Earth Surface Science Institute (ESSI) PhD Projects

Using pumping testing to detect permeability anisotropy and presence of faults in the Sherwood Sandstone Aquifer

Supervisor(s): Noelle Odling, Jared West, Piroska Lorinczi

Pump testing provides a means of investigating hydraulic properties of both aquifers and hydrocarbon reservoirs and is routinely used in hydrogeology and petroleum engineering to estimate hydraulic parameters that are required to build flow models and support aquifer and reservoir management. Pump test data from a number of observation wells surrounding an abstraction well can also be used to detect large scale structure in the vicinity of an abstraction well, including the presence of faults which act as major flow conduits or barriers. The techniques used to carry out such analysis are a topic of active research in the hydrocarbon industry but are, to date, little used in hydrogeology to detect large scale structure of aquifers.

The Sherwood Sandstone, which outcrops over large areas of north and middle England, is the UK’s second most important aquifer supplying around 25% of abstractions in England and Wales. Both water quality and water resources are an issue in this heavily exploited aquifer (e.g. Bottrell et al., 2006). It is known that the Sherwood Sandstone contains faults which may significantly impact on groundwater flow but, due to lack of exposure and geophysical data, the precise nature (conduits or barriers) and extent of their influence on fluid flow is largely unknown.  Observations from scarce outcrops (such as sand quarries) have shown that faults on a range of scales occur in the Sherwood Sandstone and that these faults contain clay and/or sand deposits (see Figures 1 and 2), probably of glacial and/or geochemical origin (Wealthall  et al., 2001, Hough et al., 2006). Thus many of these faults are likely to act as barriers or semi-barriers to flow. Borehole and outcrop observations have also indicated that the aquifer contains open fractures that enhance flow compared to the sandstone matrix alone and this has been confirmed by existing hydraulic testing. Such fractures may generate anisotropy in hydraulic conductivity which will significantly influence contaminant transport in the aquifer but little is presently known about the extent of such anisotropy.

The aim of this project is to use pump testing and associated analysis techniques to detect permeability anisotropy and the presence of faults as conduits or barriers in the Sherwood Sandstone. Pump testing will be conducted using a number of existing abstraction stations in the aquifer in collaboration with Yorkshire Water and the project will make use of numerous observation wells maintained by the Environment Agency. The results of pumping tests and their analysis will be combined with 3D modeling of groundwater flow to build improved models of the aquifer that incorporates large scale structure and permeability anisotropy. The project outcome will greatly increase the understanding of flow in the Sherwood Sandstone Aquifer and thus aid in water quality and water resource management. 

The student will be trained in methods of aquifer characterization and testing (fracture characterization, pump testing, geophysical borehole logging, dilution testing, temperature profiling) and in methods of analyzing water level data from pumped and monitoring boreholes. The project will involve fieldwork in outcrop area of the Sherwood Sandstone in England, most notably in Yorkshire and Lincolnshire. Field work will include mapping of fractures and faults in available exposures (e.g. quarries), borehole testing using geophysical logging, aquifer characterization methods such as borehole dilution testing and temperature profiling, and the installation and maintenance of instrumentation (e.g. pressure transducers) in boreholes. Analysis of background water level data and drawdown data from pump tests will be done using a variety of in-house and commercial software (such as AquiferWin32) and there may be opportunity for the student to be involved in some computer program development (e.g. using Matlab) as part of the project.

References

Allen D.J., Barker J.A., Bloomfield J.P., Robinson V.K.  1997. The physical properties of major aquifers in England and Wales. BGS, Nottingham.

Bottrell SH., West LJ., Yoshida K. 2006. Combined isotopic and modelling approach to determine the source of saline groundwaters in the Selby Triassic sandstone aquifer, UK. In: UK Permo-Triassic Red Bed Sequence. Geological Society, London, Special Publications, 263, 325-338.
Hough E., Pearce, JM., Kemp SJ., Williams GM. 2006. An investigation of some sediment-filled fractures within redbed sandstones of the UK., Proc. Yorkshire Geological Society,56, 41-53.

Wealthall G.P., Steele A., Bloomfield JP, Moss RH., and Lerner DN. 2001. Sediment filled fractures in the Permo-Triassic sandstones of the Cheshire Basin: observations and implications for pollutant transport. Journal of Contaminant Hydrology, 50, 41-51.