Impacts on groundwater quality from abandoned hydrocarbon wells - final report

Bell, R.A.; Bearcock, J.M.; Bowes, M.J.; Milne, C.J.; Scheidegger, J.M.; White, D.; Taylor, H.; Lister, T.R.; Smedley, P.L.; Ward, R.S.. 2018 Impacts on groundwater quality from abandoned hydrocarbon wells - final report. Nottingham, UK, British Geological Survey, 113pp. (CR/18/061N) (Unpublished)

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Abstract/Summary

This report details a reconnaissance investigation carried out between 2016 and 2018 from a British Geological Survey (BGS)–Environment Agency (EA) collaboration on the impacts of abandoned hydrocarbon (HC) wells on groundwater quality in England. The investigation involved collation of a database of HC wells that were identified from records provided by DECC (Department of Energy & Climate Change; now BEIS: Business, Energy & Industrial Strategy) as being abandoned (as opposed to operational or unspecified), categorising according to factors such as oil or gas designation, depth of HC resource, time since abandonment, productive life, absence of active wells nearby, and occurrence and type of overlying aquifer(s). From this categorisation, a subset of 27 sites were shortlisted for further investigation and fact sheets were produced for each outlining regional geology, hydrogeology and potential groundwater monitoring points in the area. Using these factsheets, four study areas were assessed as being most suitable for further field investigation. These comprised two gas fields: Nooks Farm (Staffordshire), and Ashdown (Sussex), and two oil fields: Hemswell (Lincolnshire) and Lomer (Hampshire). Groundwater sampling campaigns were conducted in 2016–2017 in the four study areas, with potential sampling points identified within a 5 km buffer zone around (downstream of) the HC well or HC field. In several areas, the number of sampling points was very limited as locations of HC wells do not necessarily have any relationship with locations of overlying aquifers. In others, large numbers of sites were deemed unsuitable for sampling, for reasons including disuse, decommissioning, safety or lack of access. This made representative sampling of groundwater a severe challenge. Suitable sites from the four study areas were sampled twice during the project, with a total of 48 groundwater samples being collected over the two campaigns. Results from both sampling rounds have shown that the presence of hydrocarbons in the groundwater is limited. In the first sampling round, a maximum dissolved methane (CH4) concentration of 407 μg/L was recorded. However, this relatively high value was not repeated when the site was visited during the second round of groundwater sampling. The value was below the threshold required for δ13CCH4 isotopic analysis. Some groundwater samples showed detectable quantities of organic compounds including VOCs (volatile organic compounds) and PAHs (polycyclic aromatic hydrocarbons) as well as pesticides, herbicides, fungicides, surfactants, analgesics and veterinary compounds. These were, however, almost invariably present in low concentrations, none could be linked unequivocally to the presence of abandoned HC wells and many were clearly due to other anthropogenic activities. As a result of the difficulties finding representative and suitable groundwater sampling sites, a further reconnaissance was undertaken in May 2017 to identify potential alternative gas and oil fields. This confirmed further the difficulties in finding suitable areas for investigating groundwater quality and further groundwater sampling was therefore not attempted. An alternative approach was used to investigate two abandoned HC well areas: Ashdown, one of the original study areas, and a new location at Bolney (also Sussex). A soil gas survey was completed at each of these locations in order to investigate whether soil gas proximal to the former well location contained any evidence of HC leakage. Due to poor ground conditions at the time of sampling, the results are ambiguous, but do show elevated concentrations of both CO2 and CH4. Further work in dry ground conditions would be required to say with certainty that these concentrations are linked directly to the presence of the gas wells.

Item Type:	Publication - Report
Funders/Sponsors:	British Geological Survey, Environment Agency
Additional Information. Not used in RCUK Gateway to Research.:	This item has been internally reviewed, but not externally peer-reviewed. Report made open by authors in June 2019.
Additional Keywords:	GroundwaterBGS, Groundwater, Groundwater quality, Methane and shale gas
Date made live:	05 Jun 2019 13:36 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/523676

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