Deep geothermal resources survey program: igneous, metamorphic and hydrothermal processes in a well encountering 500°C at 3729 m depth, kakkonda, japan

The exploration well WD!0a was drilled to a depth of 2618m in the Kakkonda geothermal _eld\ northeast Japan\ using e.cient borehole cooling techniques[ The well penetrated an entire shallow hydrothermal convection zone\ an entire contact metamorphic aureole and part of a neo!granitic pluton[ The recovered temperature of the well indicates a boiling point!controlled pro_le up to 279>C to a depth of 2099 m\ and a conduction!controlled pro_le with a very high gradient from 2099mto the bottom of the hole\ where the temperature is 499>C[ WD!0a may be the _rst geothermal well that encountered 499>Cwhich exceeds the conventional hydrostatic boiling!point curve[ An in~ection point of the temperature depth pro_le at 2099m and about 279>C re~ects the brittle plastic boundary[ The brittle plastic boundary constrains the maximum depth of fracture formation\ and the fracture distribution constrains the maximum depth of hydrothermal convection[ 0887 CNR[ Published by Elsevier Science Ltd