The Mise-á-la-masse Survey of Geothermal Resources using HT-8 Well in Hatchobaru Geothermal Area

The mise-a-la-masse survey has been used mostly for the ore prospecting in the mining industry. In 1984, the mise-á-la-masse survey was carried out using a casing pipe of HT-8 well in Hatchobaru geothermal area in order to map geothermal reservoirs. The measurement gave rise to the sharply contoured residual anomalies due to high contrasts of resistivities among the geothermal fluid, hydrothermaly altered zones and surrounding formations. The residual maps derived from the data processing clearly indicated several promissing low resistivity zones including the present production zone where the almost all of productive wells located inside. It was confirmed that the strike of faults which regulated the upstream of the geothermal fluid and lateral distribution of geothermal reservoirs showed a good correlation with those determined by the Schlumberger resistivity and magnetotelluric surveys in this area.