Hot dry rock geothermal energy

Hot dry rock (HDR) is an extremely abundant source of geothermal energy that is difficult to access. A vast store of thermal energy is contained within hot – but essentially dry and impervious crystalline basement rocks found almost everywhere deep beneath Earth's surface.^[1] A method for the extraction of useful amounts of geothermal energy from HDR originated at the Los Alamos National Laboratory in 1970, and Laboratory researchers were awarded a US patent covering it.^[2]

This technology has been tested extensively with multiple deep wells drilled in several field areas around world including the US, Japan, Australia, France, and the UK and investment of billions of research funds. It continues to be the focus, along with a related technique called Enhanced Geothermal System (EGS), for sizable government-led research studies involving costly deep drilling and rock studies. Thermal energy has been recovered in reasonably sustainable tests over periods of years and in some cases electrical power generation was also achieved. However no commercial projects are ongoing or likely due to the high cost and limited capacity of the engineered reservoirs, associated wells, and pumping systems. Commonly tests have opened just one or more fractures such that the reservoir surface heat exchange areas are limited. For this technology to successfully compete with other energy sources, drilling costs would have to drop drastically or new approaches that result in much more extensive, complex, and higher rate flow paths through actual fracture networks would have to be established. The enthusiasm in the research community is justified by the vast extent of the energy supply and the low environmental impact of the method, however significant breakthroughs will be required to make this a commercial energy resource.

^ Armstead, H. C. H., and Tester, J. W., 1987. Heat Mining, E. & F. N. Spon, London and New York, pp. 34–58
^ Potter, R. M., Smith, M. C., and Robinson, E. S., 1974. “Method of extracting heat from dry geothermal reservoirs,” U. S. patent No. 3,786,858

[1] Armstead, H. C. H., and Tester, J. W., 1987. Heat Mining, E. & F. N. Spon, London and New York, pp. 34–58

[2] Potter, R. M., Smith, M. C., and Robinson, E. S., 1974. “Method of extracting heat from dry geothermal reservoirs,” U. S. patent No. 3,786,858

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