5:15 PM - 6:45 PM
[SVC28-P05] Deep underground structure and hydrothermal conceptual model inferred from integrated geophysical surveys - Part2
Keywords:Kuju volcano, Otake-Hatchobaru geothermal field, Supercritical geothermal resource, Geothermal system conceptual model, Hydrothermal simulation
Kuju Volcano is located in central Oita Prefecture. Kuju-Iwoyama is one of the active volcanoes, which caused a phreatic eruption in 1995, and contains many fumaroles and hot springs. The project "Potential survey and estimation of power generation of supercritical geothermal resources in the Kuju area", funded by the New Energy and Industrial Technology Development Organization (NEDO), has been progressing in this area since 2021. This project aims to create a hydrothermal conceptual model based on geophysical, geological, and geochemical characteristics. To obtain these properties, surveys such as MT, seismic, gravity, and fumarole gas analysis have been carried out.
We developed a conceptual model of the geothermal system in this area, including the distribution of resistivity (Aizawa et al., 2022) and analysis of gas isotopes from vents and hot springs (Ishibashi et al., 2022). According to this conceptual model, some faults in the Hatchobaru area extend into the deep basement rock and may serve as pathways for magmatic fluids. In addition, the temperature distributions from boreholes drilled in this area indicate the presence of a high-temperature zone on the west side of Mt. Kuroiwa, with many seismic sources detected in this high-temperature zone. Therefore, it is possible to consider the existence of an upflow path for high-temperature volcanic fluids, possibly accompanied by magmatic fluids, in the western part of Mt. Kuroiwa.
Since the last year's report, additional knowledge has been gained through reflection seismic surveys, additional geochemical investigations, and the discovery of traces of new volcanic activity on Mt. Kuroiwa (Soeda et al., 2023). Considering these new findings, the conceptual model was updated by incorporating these results. Three-dimensional modelling of the heat-water flow was also performed based on the updated conceptual model.
As a result of this modelling, a model has been estimated that generally explains the temperature and pressure of the deep reservoir and the shallow reservoir in the Hatchobaru-Otake area where geothermal development is taking place, and we present the updated conceptual model and the results of the heat-water flow modelling.
We developed a conceptual model of the geothermal system in this area, including the distribution of resistivity (Aizawa et al., 2022) and analysis of gas isotopes from vents and hot springs (Ishibashi et al., 2022). According to this conceptual model, some faults in the Hatchobaru area extend into the deep basement rock and may serve as pathways for magmatic fluids. In addition, the temperature distributions from boreholes drilled in this area indicate the presence of a high-temperature zone on the west side of Mt. Kuroiwa, with many seismic sources detected in this high-temperature zone. Therefore, it is possible to consider the existence of an upflow path for high-temperature volcanic fluids, possibly accompanied by magmatic fluids, in the western part of Mt. Kuroiwa.
Since the last year's report, additional knowledge has been gained through reflection seismic surveys, additional geochemical investigations, and the discovery of traces of new volcanic activity on Mt. Kuroiwa (Soeda et al., 2023). Considering these new findings, the conceptual model was updated by incorporating these results. Three-dimensional modelling of the heat-water flow was also performed based on the updated conceptual model.
As a result of this modelling, a model has been estimated that generally explains the temperature and pressure of the deep reservoir and the shallow reservoir in the Hatchobaru-Otake area where geothermal development is taking place, and we present the updated conceptual model and the results of the heat-water flow modelling.