Deep Geothermal Structure and Hydrothermal System in the Otake-Hatchobaru Geothermal Field, Japan

Abstract

For the study-project of NEDO to evaluate the deep-seated geothermal potential in Japan, the Otake-Hatchobaru geothermal field, a representative fault-controlled hydrothermal system, was selected as a study area. By integrating the existing data we developed a conceptual and a numerical model of the field to represent the extent of the hydrothermal system. The conceptual model indicates that the majority of geothermal fluids discharging fiom the existing wells are supplied by a lateral flow moving above the granitic basement rocks. This interpretation is quantitatively supported by numerical simulation, Accordingly a deep reservoir of around 300?C is believed to exist near the granitic basement along faults which produce conduits for ascending fluids. We need to continue our studies through deep drilling to verify the characteristics of deep reservoirs and to ascertain whether the deep recharge is supplied fiom the granitic basement or not.