Baseline surface- and groundwater monitoring prior to an onshore shale gas operation in the Vale of Pickering, UK

Abstract

A comprehensive programme of baseline groundwater hydrochemical monitoring has been carried out in connection with the proposed hydraulic fracturing of a 2–3 km deep Bowland Shale gas reservoir in borehole KM8 at Kirby Misperton, North Yorkshire, UK. The monitoring infrastructure encompassed five on-site boreholes with hydraulically open intervals ranging from shallow weathered cover to a c. 200 m deep Corallian limestone aquifer, six off-site wells (hydraulically open in superficial materials and/or Kimmeridge Clay) and four surface-water monitoring stations. Groundwater chemistry was high stratified with depth, ranging from slightly acidic, fresh, very hard Ca–HCO 3 –SO 4 waters in shallow weathered cover, to brackish, calcium-depleted, highly alkaline waters in the Corallian aquifer. Dissolved methane was detected in most boreholes, with 10 μ g l −1 being typical of shallow boreholes and around 50 mg l −1 in the Corallian. Low ethane concentrations and isotopic evidence suggest that the methane was predominantly microbial in origin (carboxylate fermentation at shallow depth, natural methanogenic CO 2 reduction at greater depth). Elevated dissolved ethane (20–30 μ g l −1 ) was found in one well of intermediate depth, suggesting admixture of a possible thermogenic component, although this could be derived directly from the Kimmeridge Clay penetrated by the well.