Abstract
Papers relating to artificial subsurface cracks are reviewed, with special attention given to the fracture mechanics approach to the design of the artificial subsurface heat-exchange systems used in geothermal heat extraction. This approach is compared with the classical approaches which have been empoyed in oil and/or gas well stimulation. A variety of methods for mapping the artificial, subsurface cracks are also reviewed since the development of the methods is one of the key themes involved in the design of subsurface cracks. The demonstrative field experiments of extracting heat from hot dry rocks are also surveyed, since they are the best practical examples. Finally, the basic concept for the design of artificial subsurface cracks is briefly described following the successful results of the Γ-project at Tohoku university on geothermal heat extraction.
