Investigation of the Impact of Thermal Plumes on Aquifer Properties and Ground water quality

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Global energy needs are steadily rising with a predicted increase of 45% within the next 15 years. In the long-term, sustainable energy is hoped to connect economic growth to increased social equity while preserving natural resources in line with the UN sustainable development goals. Geothermal energy presents one of the key pillars to achieve this goal. The application of shallow geothermal energy systems has been increasing over the past decades with >1.7 million units installed across the EU in 2015. One of the commonly applied designs for geothermal installations are open loop systems consisting of abstraction and re-injection wells installed in the aquifer system/groundwater body to extract heat from or to inject/store heat into the aquifer. The efficiency of the system relies on the productivity of the well installations as well as suitable aquifer properties (incl. aquifer permeability & porosity). At the same time, groundwater bodies are also increasingly targeted for water supply as surface water resources become threatened by the effects of climate change. The research project will investigate the impact of thermal plumes associated with geothermal installations on aquifer parameters (e.g., porosity & permeability) and water quality. Thermal plumes are not only likely to reduce aquifer porosities & permeabilities by facilitating inorganic precipitation and secondary mineralisation but also by promoting microbial activity within the aquifer with the additional biomass adding to the reduction of aquifer porosities. This in turn will affect the overall efficiency and sustainability of the geothermal installation and reduce the sustainable yield of the groundwater body for water supplies. The project will use the Triassic Sherwood Sandstone Aquifer (SSA) as a case study example. The SSA is an important regional aquifer across central England and Northern Ireland hosting potable groundwater to depth >100m. The study will combine bench-scale tank experiments with full-scale field experiments utilising existing borehole installations at Queen's University Belfast. The study will combine the baseline characterisation of the aquifer system by completing a series of active borehole geophysical measurements, hydraulic tests, hydrochemical sampling and microbial profiling with the long-term monitoring of experimental thermal injection tests. Hydrochemical and microbial sampling & analysis will be supplemented with downhole temperature monitoring using fibre optic sensors and biogeophysical monitoring of microbial activity. Collected monitoring data will be integrated into numerical heat transport models to evaluate field-scale thermal properties of the aquifer and to better understand the impact of thermal plumes on aquifer properties. The project will be run in close collaboration with the British Geological Survey (BGS) and the Geological Survey of Northern Ireland (GSNI).