Effects of CO2 injection on shallow groundwater resources : a hypothetical case study in the Sherwood Sandstone aquifer, UK

The far-field effects of CO2 storage on onshore potable groundwater systems is examined for a hypothetical injection site within the Sherwood Sandstone Group (SSG) on the East Lincolnshire coastline, United Kingdom (UK). Using the quasi-three dimensional object-orientated groundwater flow model ZOOMQ3D, supported by conceptualisation and aquifer parameterisation of the wider hydrogeological setting, injection of 15 Mt/year of CO2 for 20 years (60 Ml/day groundwater equivalent) into the aquifer at depth is simulated. Model scenarios are carried out which test the dissipation of pressures up-dip within the storage formation. When applying typical vertical hydraulic conductivity of 10−6 m/day to the Mercia Mudstone Group (MMG) caprock groundwater pressure heads in the shallow confined SSG aquifer, 60 km up dip, where it is used for potable water supply, increase by 0.01–10 m. Groundwater levels within the unconfined aquifer, 80–100 km up-dip from the injection zone, increase by <0.01–1 m with a corresponding increase in river flows of approximately 1.7%. Two important points are observed, firstly that the degree of impact on shallow groundwater systems is highly sensitive to the vertical leakage assigned to the caprock. When the leakage co-efficient is increased by one order of magnitude groundwater heads in the potable aquifer are reduced by two orders of magnitude. Secondly, that the response of groundwater pressure heads to injection is rapid, as is the subsequent recovery. Using a groundwater model, in addition to detailed reservoir modelling, provides a useful tool to assess the potential scale of impact of CO2 storage on shallow groundwater systems and can be used to aid the regulation of such operations. © 2012 Natural Environment Research Council (NERC). Published by Elsevier Ltd. All rights reserved