Structural controls on geothermal systems in the Northern Volcanic Zone, Iceland

The world moves necessarily towards finding cleaner, more sustainable energy sources to ensure reductions in carbon emissions whilst looking to provide for the world's energy needs. As a globally available form of clean energy, geothermal will have an ever more important part in this process, with the high-energy outputs of geothermal systems in volcanically active areas such as Iceland playing a key role. As such, it is crucial to ensure that future geothermal site exploration both maximises geothermal potential and ensures sustainability of the underlying geothermal system.

Subsurface structures, from large-scale bounding faults through to distributed networks of fractures, can act as boundaries and limits to the distribution of heat and fluids within volcanically driven geothermal systems (e.g., Eugenio et al., 2020). Fracture networks, acting as either conduits or barriers to fluid flow, are key for providing sustainable routes for fluid extraction and recharge (e.g., Perez-Flore et al., 2016). Poor understanding of the constraints these provide can lead to over-exploitation and a reduction in the longevity of the geothermal system and impact the surrounding environment (e.g., Bromley et al., 2013). As such, understanding the mechanisms of these structures and how they limit or act as conduits to fluid flow is key for both determining the useable extent of the geothermal system and for assessing the likely impact of fluid extraction and future changes to stress environments on both the structures and the long-term sustainability and usability of the subsurface geothermal environment.

With primary focus on the Theistareykir geothermal system, this project will use the wealth of data acquired by Landsvirkjun during geothermal energy production at both Krafla and Theistareykir sites, to compare and contrast structural controls of these two volcanically driven geothermal systems. The project will build upon the numerous studies that make use of an additional range of geological and geophysical data and methods from across the two sites, for example, surface fault mapping, geochemical analysis, micro-seismic mapping, fracture network models, seismic profiling (e.g. Hjartardottir et al., 2014, Khodayar et al., 2018, Scott et al., 2019, Millet et al., 2020) and conceptual models of the geothermal systems (see figure 2) (e.g., Mortensen et al., 2009, Saby et al., 2020). This project will look to understand how structures, from larger bounding faults through to distributed fracture networks, work as controls on fluid and heat flow in the geothermal system. It will look to examine the mechanics of how fault structures act as boundaries for a geothermal system, investigating how these might change following fault reactivation and the impact of these changes to the boundary conditions and constraints of the geothermal system. Additionally, the project may have the opportunity to incorporate data from newly drilled geothermal wells in the south of the Theistareykir geothermal fields, currently planned to start within the duration of the project