Seismic for geothermal
Geothermal exploration is underpinned by subsurface understanding. Mark Ireland, Charles Dunham and Jon Gluyas make the case for UK government-supported seismic data acquisition
Modern seismic nodal systems (shown here) are compact, require little space and can be easily deployed, even in built-up areas
In 2021, almost half of energy demand for buildings globally was for space and water heating (IEA, 2022). In the UK, the heating of buildings (homes, commercial and public) accounts for 23% of carbon emissions, so, as part of a least-cost pathway to meet our net-zero commitment, the government has set a target of 18% of the national heat demand to be met by heat networks by 2050 (DESNZ & BEIS, 2021; updated 2023). Deep, low-enthalpy geothermal energy (typically resources located at depths greater than 500 m) could offer a baseload for heating (and cooling) and significantly contribute to the expansion of our low-carbon heat networks (Gluyas et al., 2018). The utilisation of low-enthalpy geothermal energy for heat is established (Agemar et al., 2014), but the successful exploration and characterisation of geothermal resources requires subsurface geoscience data.
Figure 1: Location of existing seismic data compared to built-up areas. Most seismic data come from the Carboniferous Basins of Northern England and the Midlands, or the Mesozoic Basins of Southern England. Data density varies dramatically, with the greatest coverage of 2D data located across the Wessex and East Midlands Basins. At a more granular scale (top right panel, Bournemouth to Portsmouth, and lower right panel, Northeast England), while data coverage exists, it is absent across built-up areas.
Current data
Seismic reflection surveys and borehole data allow geoscientists and engineers to carry out comprehensive assessments of geothermal resource potential. However, the cost of such data acquisition means that currently most assessments rely on legacy data. To date, the UK has only sparse coverage of seismic data, confined largely to areas targeted for petroleum exploration between the 1910s and 2000s. In many areas of high heat demand, such as built-up urban areas, there is no seismic data coverage (Ireland et al., 2021). Three-dimensional seismic reflection data from onshore cover less than 3,000 km2 (or 1%) of the landward area, yet those built-up areas likely most suited to the development of heat networks cover an area of 14,141 km2 – and rarely do these areas overlap (Fig. 1).
Recognising that the lack of data coverage limits or prevents organisations from making informed evaluations of the potential for geothermal energy for heating projects, many European countries, including the Netherlands, Germany and Belgium, have embarked on dedicated seismic surveying. For example, as part of the Dutch SCAN Programme in the Netherlands, 1,811 km of 2D seismic data were acquired (Rehling et al., 2023). It is essential that the UK also embarks on a programme of publicly funded seismic data acquisition for the super-low-carbon, sustainable, renewable heat resource that occurs below everyone’s feet.
Technological transformation
As recently as 2015 the UK government funded seismic data acquisition for oil and gas exploration on the UK Continental Shelf in areas with few existing seismic data (OGA, 2015). During this programme, ~20,000 km of 2D seismic data were acquired at a cost of £20 million. A similar injection of funds for a data acquisition programme that targets the seismic imaging of the deep onshore subsurface has the potential to highlight opportunities for geothermal exploration across the UK.
We’re not the first to suggest this. The BGS made a similar plea in 2020 (Abesser et al., 2020). So what has changed? In the UK, there is limited practical experience of how far seismic acquisition technologies have come. Most recent 3D seismic surveys for oil and gas in the UK used cabled systems and dynamite. However, industry leading technologies are dramatically changing the speed of surveys, minimising their impact, and ultimately reducing the cost, while at the same time significantly improving the quality of the seismic data obtained. Buildings and infrastructure traditionally make onshore seismic data acquisition in urban areas challenging and logistically complex. Now nodal seismic receivers remove the requirement for cabled systems and allow ultra-high density seismic acquisition onshore, with improved safety and reduced environmental impact. New-to-market seismic sources, for example eVibes, an electric seismic source that uses a direct drive electromagnetic motor, enable compact sources to be built, while achieving the required depth of penetration (Tranter et al., 2022).
De-risking geothermal at scale
A government-supported programme could provide a scalable and cost-effective mechanism for seismic data acquisition across multiple areas of the UK. An alternative to central government support could be for multiple regional and local government agencies to collaborate. This approach could adopt the oil and gas sector, multi-client acquisition model, where seismic surveys are acquired by a seismic acquisition company over multiple areas of interest (Micenko, 2016). With the acquisition to be underwritten by regional and local government, the subsequent data could be made available to freely (or at a very low cost) support development of the nascent geothermal sector and ultimately the decarbonisation of heat in the UK.
Seismic reflection data provide confidence in drilling targets, and while the cost of 3D seismic is much higher than 2D, experience from the oil and gas sector shows that the success rate of drilling is improved significantly when using 3D over 2D seismic data (Aylor, 1999). As highlighted by David Banks (page 28), for deep geothermal resources to be a promising option for low-cost and low-carbon heat requires a reservoir target at depth with favourable characteristics identified through play-fairway analysis – which is exactly where seismic data come in.
Geophysical surveying alone will not unlock the geothermal potential of the UK. However, it will enable the interpretation of the structural and stratigraphic architecture of sedimentary basins, thereby supporting informed decision making ahead of the capital expenditure associated with drilling, where well costs could be between £1.6 and
£1.8 million per kilometre (Arup, 2021).
Field acquisition equipment at RAF Leeming. Modern nodal systems (as shown in the main article image) are compact and require little storage space. Enough nodes for a high-density survey over a built-up area could require as few as four pallets of receivers. Nodes can be deployed by small teams (pictured, top). Newcastle University employed a lightweight, tractor-mounted weight drop (pictured, left) and acquired a good seismic image to ~1 km depth.
CASE STUDY: Newcastle University – RAF Collaboration
In a first of its kind for the UK, Newcastle University recently acquired a high-density 3D seismic survey as part of a collaborative project with the RAF, utilising STRYDE nodal receivers. The survey deployed 3,271 nodal seismometers across a ~5 km2 area at RAF Leeming in North Yorkshire. Taking advantage of the latest nodal technology enabled the simultaneous acquisition of passive and active source seismic surveys, with reduced logistical and operational complexity and zero impact on continuous operations at a site with intricate ongoing activity. The reduced entry cost associated with the deployment of lightweight nodal systems and the use of a lightweight, low-impact seismic source, together with the ease of deployment, enabled data acquisition that until recently would have been prohibited by traditional cabled systems.
Dr Mark Ireland
School of Natural and Environmental Sciences, Newcastle University, UK
Dr Charles Dunham
School of Natural and Environmental Sciences, Newcastle University, UK
Prof Jon Gluyas
Department of Earth Sciences,
Durham University, UK
Acknowledgements
Newcastle University thanks STRYDE for the support of the geophysical surveying at RAF Leeming and Rees Geophysical for providing the source for surveying activities surveying.
Further reading
A full list of further reading is available at geoscientist.online
• Abesser, C. et al. (2020) Unlocking the potential of geothermal energy in the UK; British Geological Survey, 22pp. (OR/20/049) (Unpublished); www.nora.nerc.ac.uk
• Agemar, T. et al. (2014) Energies 7, 4397–4416
• Arup (2021) Deep Geothermal Energy: Economic decarbonisation opportunities for the United Kingdom; www.r-e-a.net
• Aylor, W. J. Jr. (1999). J. Pet. Technol. 51 (06), 52–56, SPE-56851-JPT
• Banks, D. (2023) Geoscientist 33(3), X-Y
• DESNZ & BEIS (2021) Heat and buildings strategy; www.gov.uk (updated 2023)
• Gluyas, J. et al. (2018) Proc. Inst. Mech. Eng. Part J. Power Energy 232, 115–126
• EA (2022) Heating, IEA, Paris; www.iea.org
• Ireland, M. T. et al. (2021) Front. Earth Sci. 9
• Micenko, M. (2016) Seismic window: The age of multi-client seismic. CSIRO Australia. Preview, 34–34; www.publish.csiro.au
• OGA (2015) OGA completes data acquisition in £20m UK seismic campaign; www.gov.uk
• Rehling, J. et al. (2023) First Break 41, 33–43
• Tranter, N. et al. (2022) First Break 40, 47–5
