The Impact of Subsurface Heterogeneity on the Performance of Aquifer Thermal Energy Storage (ATES) Systems

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. In this context, geothermal energy present one of the potential 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. A particular design of open loop geothermal installations support Aquifer Thermal Energy Storage (ATES) systems which allow the seasonal storage of waste heat in the subsurface for subsequent use to meet heating demands. The efficiency of the system relies on the productivity of the well installations as well as suitable aquifer properties (incl. aquifer permeability & porosity and thermal properties).

The planned research project will investigate the impact of subsurface heterogeneity on the performance of ATES installations. Subsurface heterogeneities may be associated with depositional features of sedimentary aquifers or discontinuities such as fractures, igneous intrusions or faults and may affect hydraulic and thermal properties of the host rock. These heterogeneities may affect the groundwater flow regime within the aquifer unit and impact on ability of the aquifer to store and conduct heat. This in turn may ultimately affect the overall efficiency and sustainability of the ATES installation.

The project will use the Triassic Sherwood Sandstone Aquifer as a case study example. The Sherwood Sandstone Aquifer is an important regional aquifer across central England and Northern Ireland that hosts deep potable groundwater to depth >100m. The study will combine full-scale field experiments utilising existing borehole installations at Queen's University Belfast with numerical modelling studies. The study will combine the baseline characterisation of the aquifer system by completing a series of active borehole geophysical measurements, hydraulic borehole tests, with the long-term monitoring of experimental thermal injection tests using fibre optic distributed temperature sensing. Collected monitoring data will be integrated into numerical heat transport models to evaluate field-scale subsurface properties to better understand the impact of aquifer heterogeneity on system performance.