A Hot Dry Rock geothermal reservoir has been created at a depth of 2000 m in granite. The stimulation was carried out using 40 000 mí (10 million US gal) from a 350 m open hole section that had been treated with a purposedesigned explosive tool. On-line seismic mapping has shown that the reservoir has developed in the direction of the maximum principal stress despite the fact that the joint directions are not orientated in that direction. Photographic and television inspection has been used to correlate acoustic seisviewer and conventional wire logging results including observations of fracture width at the wellbore during pressurisation. Downward growth of the reservoir has been observed despite the fact that the stimulation fluid was fresh water. This has been explained tentatively as predominantly shear growth because the shear stress gradient is subhydrostatic due to the highly anisotropic stress field. Preliminary calculations have shown that the reservoir structure has a volume of 100-200 million mí but there is no direct, low resistance flow path between the wells and the residence time is in excess of 5 days.

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