The Role of Salt Tectonics in the Energy Transition: An Overview and Future Challenges

Abstract

In this paper we examine the role salt tectonics can play in a number of key energy transition technologies, namely, energy storage as gas in salt caverns (e.g. hydrogen and compressed air), CO2 storage, and geothermal energy. For each of these technologies we explore: i) fundamental concepts and driving forces; ii) how and why the properties of salt are of importance; and iii) the key salt-related technical challenges, potential future research directions, and technical approaches needed for large-scale development. We highlight how salt-bearing basins offer vast potential for development throughout the energy transition including, but not limited to: i) the likely demand for thousands of new hydrogen storage caverns inside salt bodies by 2050; ii) a likely early focus for porous media CO2 storage sites in basins strongly influenced by salt tectonics; and iii) enhanced geothermal energy potential in and around salt bodies. Effective exploitation of these resources will require a deeper understanding of the internal composition, geometry, and evolution of salt structures and their surrounding sediments, and potentially the development of more predictive models of salt tectonic behaviour. Critically, we see the need to integrate learnings of salt tectonics gained in the academic, mining, solution mining, and oil and gas communities, and apply a fresh perspective to answer research questions of relevance to the energy transition. Developing this new understanding will help optimise design, reduce geotechnical risk, and improve efficiency for energy transition technologies, thus indicating a strong future demand for salt tectonic research.

Experimental study of geophysical and transport properties of salt rocks in the context of underground energy storage

“…The presence of structural discontinuities and heterogeneities (e.g. shape, orientations and composition of insoluble lithologies, halite fabric and stress‐related microstructural changes; Field et al., 2019) influences largely the safety and placement of salt caverns that may be used for UHS activities (Cyran, 2020; Duffy et al., 2023). We have observed how vertical discontinuities that control fluid migration (dispersion or channelling) may be undetectable from acoustic P‐ and S‐wave attributes (i.e.…”

“…Salt caverns are meant to play an important role in the net-zero energy transition challenge, initially covering short-term fluctuations in energy demand (e.g. Duffy et al, 2023) and serving also as safe locations for seasonal and long-term underground hydrogen storage (UHS) (Tarkowski & Czapowski, 2018). The process of solution mining and cavern formation at shallow depths (where halite is not in a plastic deformation regime) involves (i) injecting water using injection tubing to dissolve the underground salt and form brine and (ii) extracting the brine solution to surface with a production tubing set, sufficiently below the injection point to extract the higher density brine flowing downwards (Fokker, 1995).…”

The potential of salt-embedded basins for energy transition. The Estopanyà and Boix synclines (South-Central Pyrenees) as outcrop analogues of a geothermal reservoir

“…Due to the almost impermeable character of salts, they have been broadly studied for natural gas and petroleum reservoirs as potential seals and hydrocarbon traps (e.g., subsalt traps, Evans et al, 1991;Magri et al, 2008;Urai et al, 2008;Warren, 2016). Moreover, the rheology of halite and other chlorides allows them to migrate from deep to shallower locations, at the time they modify the geothermal gradient due to their high thermal conductivity (i.e., salt-chimney effect, O'Brien and Lerche, 1984 In this context, salt diapirs and walls and their anking sedimentary successions are being proposed for an increasing amount of carbon-neutral and decarbonization purposes, like the emplacement of salt caverns for subsoil hydrogen storage (Lankof and Tarkowski, 2020;Lankof et al, 2022;Muhammed et al, 2022;Allsop et al, 2023) Carbon Capture and Storage (CCS) (Evans and Holloway, 2009), or geothermal energy production (Huenges, 2016;Daniilidis and Herber, 2017;Duffy et al, 2023). Contrary to the non-porous, low permeable, and highly thermal conductive halite, salt-anking sedimentary rocks show signi cant compositional and petrophysical variability depending on factors such as lithology, diagenesis, and fracturing (Sass and Götz, 2012;Moeck, 2014;Rowan et al, 2020a;Mitjanas et al, 2024).…”

“…Therefore, salt structures and their associated sedimentary basins may constitute proper analogues of sedimentary reservoirs sealed by evaporites, which often include high thermal conductive salts such as halite (over 6 Wm − 1 K − 1 at 20 ºC, Clauser and Huenges, 1995). This scenario puts saltembedded basins and minibasins in the focus of geothermal exploration as potential targets (Raymond et al, 2022;Duffy et al, 2023;Marín et al, 2023) (Fig. 1).…”

Characterising the internal structural complexity of the Southern North Sea Zechstein Supergroup Evaporites

“…Much of the current understanding of evaporite sequences has come from their association and the subsequent data acquisition with prolific hydrocarbon provinces, such as the Precaspian Basin (Rowan et al, 2019), the South Atlantic conjugate margins (Blaich et al, 2008; Wen et al, 2019), the Zagros basin (Amthor et al, 2005; Bordenave & Hegre, 2010) and the North Sea (Peryt et al, 2010), where sequences are important for both trapping geometries and seals (Archer et al, 2012; Sarg, 2001). Similarly, evaporite formations will likely be important components in many subsurface developments required for the energy transition, in particular for geological storage sites (Duffy et al, 2023).…”