The Potential For The Exploitation Of Geothermal — страница 4

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density.? Over half the resources are located in east Yorkshire and Lincolnshire, essentially rural areas lacking concentrated populations.? The other UK areas are little better, though several large conurbations in the midlands and North West could benefit form geothermal schemes such as that in Southampton.? For example, there has been discussion about reopening and exploiting the Cleethorpes well if high flow rates could be maintained at around 50°C (see Boyle, G10 p388).? Should fossil fuel prices ever escalate again, no doubt geothermal aquifers in the UK will receive much more attention than at present.Hot Dry Rock Technology (HDR)When asked whether there is potential in the UK for geothermal electricity production Dr Robin Curtis of GeoScience Limited stated ?there is no

potential for electricity power generation in the UK other than by Hot Dry Rock Technology which is still being developed in a few other countries but is currently on hold in the UK?.Hot Dry Rock technology is often referred to as ?heat mining? and aims to exploit volumes of hot rock that contain neither enough permeability nor enough ?in situ? fluid in their natural state for commercial exploitation.? The permeability is created by stimulation techniques and the fluid is placed and circulated artificially (see Ledingham, P1 p4).Research on hot dry rock technology began in the 1970?s to develop reservoir creation and exploitation techniques that would allow access to an almost limitless resource base virtually independent of location. The original dream behind HDR concept was

that if a method could be found to induce permeability into basement rocks that would not otherwise support significant flows of water, then this would give access to the huge amount of thermal energy stored within the accessible layers of the Earth?s crust.Such a resource would be available virtually everywhere, would reduce dependence on imported fuels, provide temperatures adequate for electricity generation even in tectonically stable regions, and would discharge very little waste and almost no greenhouse gases (see Ledingham, P11 p296).Of the three principal granite zones in the Eastern Highlands, Northern England and Southwest England, the latter is characterised by the highest heat flow, as shown in (Appendix 5a).? However, large areas of the more northerly granite masses

are covered by low thermal conductivity sedimentary rocks and so, from The Heat Conduction Equation, temperatures will be higher at depth than if the granite bodies came to the surface.By the mid-1980s, detailed evaluation of the radio-thermal and heat conduction properties of all the granite areas still demonstrated, as shown in (Appendix 8a), that the South-West England granite mass is the best HDR prospect.? Substantial areas of Cornwall and Devon are projected in (Appendix 8b) as having temperatures above 200°C at 6km depth and it has been estimated that the HDR resource base in South?West England alone might match the energy content of current UK coal reserves.? One estimate suggested that 300-500MW (about1016Ja-1) could be developed in Cornwall over the next 20-30 years

with much more to follow later (see Boyle, G10 p388).? However, for technological and economic reasons, the pace of progress is unlikely to be that fast.The principle of HDR technology is to circulate a fluid between an injection well and a production well, along pathways formed by fractures in hot rocks. A deep heat exchanger is then created, and the fluid transfers heat to the surface, where it can be converted to electricity. This process is contained in a closed-loop and no gas or fluid escapes in the atmosphere. The hot fluid produced under pressure at the wellhead flows through a heat exchanger, vaporizing a secondary low-boiling working fluid This fluid, usually isobutane, is then passed through a turbine driving an electric generator (Appendix 10) (see reference16).Since

the early days of HDR research, the main question has been whether HDR technology can be made to work, i.e. whether a sufficiently large heat exchanger with acceptable hydraulic properties can be created in rock of low natural permeability so that economic quantities of heat can be extracted. The only method of testing the concept and of developing the techniques for engineering the reservoir is via large-scale field experiments. The UK-project in Rosemanowes, Cornwall was the second such project to be initiated and has produced a great deal of new information about deep crystalline rock masses and techniques to investigate them (see reference15). The Experiments with HDR carried out at Rosemanowes in Cornwall served to demonstrate some of the outstanding uncertainties in HDR