Engineered Geothermal Programme in the UK

Proceedings World Geothermal Congress 2010 Bali, Indonesia, 25-29 April 2010 Engineered Geothermal Program in the UK R. Baria1, G. MacPherson-Grant1, J. Baumgaertner2, A. Jupe3 and J. Cowles3 1EGS Energy UK Ltd. Penzance, Cornwall, TR18 4SL UK, 2BESTEC GmbH, Landau, D-76829 Germany, 3altcom Limited, Penzance, Cornwall, TR18 4SL UK [email protected], [email protected], [email protected], [email protected], [email protected] Keywords: Keywords: Engineered Geothermal System Geothermal energy is generally categorised as a “new (EGS), Geothermal Energy and UK EGS resource. renewable energy” but that is not the case in the short to medium term. Depending on the type of geothermal ABSTRACT resource, it may take anything up to 20,000 years to recover naturally the energy extracted from an exhausted Recent uncertainty in the supply of energy and the effect of Engineered Geothermal System. global warming raised a call for a review of the potential of geothermal energy in the US. A study was commissioned Geothermal energy has been used by people since the dawn by the US DoE via Massachusetts Institute of Technology. of civilisation in many parts of the world for bathing and The study concluded that if Enhanced Geothermal System washing clothes from hot springs, an expression of technology was pursued seriously then it was anticipated geothermal energy on the surface, Cataldi, et al., (1999). that something like 11,000GWe could be generated by Similarly, when geothermal energy is mentioned, the 2050. general public perception is that it is found in places such as New Zealand, Iceland, etc. on the crustal boundaries where Similarly, in 1986 an assessment was carried out by the the crust is thin, i.e. from hydrothermal fields. Nothing can Camborne School of Mines which indicated that a mature be further from the truth, as we all know that the Engineered Geothermal System (EGS) technology could temperature normally increases as one goes deeper into the supply around 10% of the electricity demand in the UK for earth’s crust. This means that to access the right around 200 years. Both of these assessments show that temperature to exploit geothermal energy one would have there is a vast energy resource which can supply base load to go deeper in some parts of the world and shallower in 24 hours a day continuously with virtually no effect on the others. To extract the geothermal energy economically, it environment. makes sense to extract it from shallower depth first and The concept of EGS itself is very simple but the deeper at a later date to take advantage of the improvement development of the associated technology has taken longer in the deep drilling technology and increasing price of than anticipated. Following the technological success at the energy. European project in Soultz, France, and a commercially Although the initial idea of exploiting the heat resource at funded EGS plant in Landau, Germany, it was just a matter depth was developed at Los Alamos and named “Hot Dry of time before the UK participated in the exploitation of this Rocks”, the technology to exploit it has gone through a technology. number of innovations. Associated titles such as “Hot Wet In the 80’s the UK helped to pioneer the development of Rock”, “Hot Fractured Rock”, “Enhanced Geothermal this technology by establishing ground rules for the System”, etc. have been given to try to fit it to a specific in migration of fluid in specific stress conditions, which are situ geological condition. Although Los Alamos was the fundamental to the development of this technology. An front runner during the 1970’s, the concept appealed to International Conference on EGS (Hot Dry Rock) was Japan and Western Europe and the centre of gravity of this organized in 1989 and the proceedings were published to technology moved to Western Europe between the late highlight the resource available in the UK and the progress 1980’s and the present day. made to date on this technology, Baria, R. (1990). As the technology continued to develop to address new In view of the large resource in the UK and the current state challenges, it became evident that solutions were required of the technology, a company has been established to to be engineered to fit with the local conditions at depth. exploit the EGS potential in the South West of England. This lead to acceptance of the title “Engineered Geothermal The first phase is a background study to identity a favorable Systems” (EGS) as there is likely to be some variation in resource area and to develop a work plan to exploit it. The the in situ condition and an engineering solution will be company, EGS Energy Ltd, includes BESTEC GmbH and required to address it. The advantage of this approach altcom Limited as partners, thus reinforcing the reduces the risk of classifying it into specific concepts and technological and management potential of the company. termination of the project if it does not fit into the preconceived idea. Considering this as an EGS reduces this type of risk and premature termination of projects, as from 1. INTRODUCTION past experience one can find a solution to meet the new At the 2005 Annual Geothermal Resource Council’s challenge. meeting in Reno, the title for the book of Abstracts was “Geothermal Energy - The World’s Buried Treasure” and 2. EGS DEVELOPMENT IN THE UK how true this is. The general public at large is not aware of the potential of Geothermal Energy in being able to supply The United Kingdom, like many parts of the world, is not a major portion of our primary energy needs. fortunate enough to be on the crustal margins and therefore does not have the advantage of high temperature at shallow depth and the likely presence of exploitable quantities of 1 Baria et al. fluid at these depths for hydrothermal operations. The UK’s Devonian and Carboniferous basinal sediments, which research on the EGS project at the Rosemanowes site probably developed on thin continental crust, between 1976 and 1993 made a significant contribution to Willis-Richards, et al. (1986). The partly exposed granite the understanding of the physical process involved in the batholith extends for 200km along the spine of SW creation of an EGS reservoir: diagnostic methods to England, and probably extends further to the west across determine its physical parameters, developing techniques to the continental shelf. interpret the data and the potential EGS resource in the UK. The EGS programme at Rosemanowes was specifically Exposed granite copulas are characterised by heat flows of tailored to keep it under 100°C so that the technology from between 110 and 135mW/m2 compared to regional values the oil and gas industry could be used to understand the of 60-5mW/m2, Tammemagi and Wheildon (1974), Francis physical processes involved in the development of an EGS (1981), see Figure 1. technology. The radiogenic internal heat production of granite samples During the latter part of the project, development of averages about 5.0µW/m3, compared country rock values reservoir creation modelling (FRIP); high temperature close to 2.0µW/m3. No significant variation in heat instrumentation (220°C); diagnostic techniques such as production is observed down the 2.6km vertical section of microseismic monitoring, engineering assessment for a the deepest wells at the Rosemanowes site. This lack of deep system, the UK potential EGS resource, etc. were vertical fraction of the radiogenic heat producing elements prepared to lead the existing programme to the next phase is likely to be a general property of peraluminous S-type of the development of going down to 6000m depth to granites such as that found under SW England, Webb, et al. exploit the EGS resource at 200+°C. A review was carried (1985), Sawka (1986). If the heat producing contrast out by the Department of Trade and Industry (DTI) at the between the granite and the country rock measured near the time and based on the limited data, it was concluded that surface is maintained over the entire 10 to 15km thickness the technology was not economically attractive, even of the granite batholiths, Tomb (1977), Al-Rawi (1980), though the resource assessment showed that the accessible then the heat flow anomaly can be attributed entirely to the EGS resource was vast and had the potential of supplying high heat productivity of the granite batholiths, without any around 10% the UK’s electricity requirement for 200 years. contribution from entire lower crust or mantle. 3. CONSOLIDATION OF EGS RESEARCH IN W. EUROPE During this period, it became apparent that a demonstration EGS project at greater depth was needed to address commercial parameters and technology. It was also recognised that significant funding from the European Commission (EC) would be required. Realignment took place and a European EGS project was established at Soultz, France, in 1988 with funding support from the EC, Germany, France, and - in the early stages - from the UK. The research on EGS carried out at Soultz lead to a number of conclusions - some of them are listed below: Figure 1: Heat Flow Measurements in the Carmenellis a. Tensional regimes such as grabens are relatively Area with Figures Large Enough to Read easier to manipulate then compressive stress regimes. Modelling of the EGS resource was established taking into b. Open systems and closed systems required a consideration the shape of the granite (gravity survey, different approach for designing a circulation density measurements, seismic survey, outcrop and system. information from deep wells etc) 3D thermal modelling c. Fluid is likely to flow proximately in maximum (heat flow, heat production, regional heat flow, thermal principle stress direction and is controlled by the conductivity, etc.) thermal resource (temperature with depth in situ stress and joint network.

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