Title: Quantitative investigation of potential geothermal systems in Ireland
Researchers: Dr Sarah Blake, Prof. John Walsh
The need to reduce greenhouse gas emissions is an important issue facing society at present, and EU member states have agreed to a 40 % reduction in emissions by 2030 . Renewable energy, including geothermal energy, will play an important role in achieving this goal. Appropriately designed, large-scale geothermal energy systems can satisfy society’s “energy trilemma”, by providing a secure energy supply that is economical and environmentally sustainable. In 2015, heat production accounted for 39 % of the total annual energy expenditure in Ireland. Currently, renewable energy contributes 6.5 % to this heat energy expenditure, and our national target is 12 % by 2020. Although there are currently no large-scale, deep geothermal heating projects in Ireland, it is nonetheless feasible that geothermal energy can provide a sustainable and stable supply of heat energy to help us meet this national target. In many locations worldwide, well designed, deep geothermal systems are providing affordable, large-scale heating and cooling solutions and reducing greenhouse gas emissions (e.g., Paris, France; Southampton, United Kingdom; and Heerlen, the Netherlands. Geothermal energy potential depends largely upon the amount of heat available (dependent on temperature and volume of water). The installation of such a system commonly involves drilling a series of deep wells, which facilitate the abstraction of heated waters and the re-injection of the relatively cooled wastewaters. This undertaking consequently requires an advanced and site-specific understanding of the geology, hydraulic properties, groundwater chemistry and geothermal gradient of any proposed geothermal system.
Ireland is located far from any active plate boundaries and is non-volcanic and largely aseismic. As a result, the geothermal gradient is quite low at about 25 °C/km on average in the centre of country . Therefore, any geothermal energy available in Ireland is most likely to be low-enthalpy (< 150 °C at economically feasible depths). Low-enthalpy geothermal settings are being exploited for large-scale heating projects in the examples given above, using groundwaters with temperatures as low as 31 °C (Heerlen, the Netherlands). These systems are well-proven, commercially successful projects. Neither the geothermal gradient nor the hydrogeological setting in Ireland precludes the presence of significant low-temperature geothermal resources at depth.
The geothermal energy potential of Ireland was assessed in the SEAI Geothermal Energy Resource Map of Ireland , and also during the SFI-funded IRETHERM project, which primarily used electromagnetic geophysical surveys over strategic geothermal target types. From a practitioner’s perspective, both the SEAI report and the IRETHERM project were hampered by a lack of deep borehole data in Ireland. For the IRETHERM project, the geothermal targets were chosen for their geothermally favourable geological attributes rather than their location close to potential end-users of the energy. The results of IRETHERM identified several lithologies with promising heat production rates (granites and shales), large volumes of permeable sandstones at depth in Northern Ireland , and highlighted the likely importance of Cenozoic strike-slip faults in the circulation of hydrothermal fluids. The aim of this project will be to build upon this previous research in a pragmatic way by investigating the geothermal plays of specific Irish sites with the objective of identifying promising sites for future geothermal systems and exploration boreholes. This project will bridge the gap between purely academic research and the implementation of geothermal systems in an Irish setting