Hirofumi Muraoka

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

Abstract 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.

Development of the Vertical Electro Magnetic Profiling (VEMP) method

Abstract As a part of the “Deep-Seated Geothermal Resources Survey (DSGR)” project being undertaken by the New Energy and Industrial Technology Development Organization (NEDO), the “Vertical Electro Magnetic Profiling (VEMP)” method is being developed to accurately obtain deep resistivity structures. The VEMP method takes multi-frequency three-component magnetic field data in an open hole well using controlled source transmitters emitted at the surface (either loop or grounded-wire sources). Numerical simulations using EM3D have demonstrated that phase data of the VEMP method is not only very sensitive to the general resistivity structure, but will also indicate the presence of deeper anomalies. Forward modelling was used to determine the required transmitter moments for various grounded-wire and loop sources for a field test using the WD-1 well in the Kakkonda geothermal area. VEMP logging of the WD-1 well was carried out in May 1994 and the processed field data matches the computer simulations quite well.