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

• Published in: Geothermics Vol. 27; no. 5; pp. 507 - 534
• Main Authors: Muraoka, Hirofumi, Uchida, Toshihiro, Sasada, Masakatsu, Yagi, Masahiko, Akaku, Kohei, Sasaki, Munetake, Yasukawa, Kasumi, Miyazaki, Shin-ichi, Doi, Nobuo, Saito, Seiji, Sato, Ko, Tanaka, Shoichi
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 14.08.1998
• Subjects: deep drilling; geothermal resources; granitic pluton; high temperature; Japan; Kakkonda; metamorphic aureole; Kakkonda; granitic pluton; metamorphic aureole; Japan; deep drilling; geothermal resources; high temperature
• ISSN: 0375-6505; 1879-3576
• DOI: 10.1016/S0375-6505(98)00031-5

The exploration well WD-1a was drilled to a depth of 3729 m in the Kakkonda geothermal field, northeast Japan, using efficient 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 profile up to 380°C to a depth of 3100 m, and a conduction-controlled profile with a very high gradient from 3100 m to the bottom of the hole, where the temperature is 500°C. WD-1a may be the first geothermal well that encountered 500°C, which exceeds the conventional hydrostatic boiling-point curve. An inflection point of the temperature–depth profile at 3100 m and about 380°C reflects 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.