| Title | Numerical modeling of hydrothermal system in the western region of Kirishima volcano in Kagoshima Prefecture, Japan |
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| Authors | T. Amane, N. Jun |
| Year | 2024 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Kirishima Volcano, hydrothermal system, conceptual model, numerical model |
| Abstract | Well-developed geothermal areas exist in the Ogiri and Shiramizugoe areas, located in the western part of the Kirishima Volcano. As understanding the hydrothermal system is extremely important for sustainable geothermal development, numerical models of hydrothermal systems under natural conditions have been developed to investigate both areas. However, the reproduction of pressure profiles in this area remains an issue, and one possible reason is the existence of an impermeable layer between the Ogiri and Shiramizugoe areas. Thus, in this study, we classified the part of the NW fault between the Ginyu and Shiramizugoe faults that are distributed in a high-density area, estimated from the airborne gravity anomaly method survey (Nishijima, 2016). We created a model wherein the Ogiri and Shiramizugoe areas are independent of each other by the impermeable layer owing to low permeability. Simulations were conducted using HYDROTHERM-Version 3.2 (Kipp et al., 2008) to investigate the hydrothermal system. The simulation results indicated that the calculated pressure profiles of the wells located in the target area were approximately 5 MPa higher than the measured values. As all voids in this model were saturated with water up to the surface block, the differences between the calculated and actual groundwater levels can be attributed to the fact that the calculated pressure values exceed the measured values. Therefore, when the influence of the groundwater surface is corrected using the pressure determined from the simulation, the pressure difference between the Ogiri and Shiramizugoe areas can be reproduced. Therefore, we developed a model that can explain the temperature and pressure in this area by reducing the permeability of the NW fault distributed in the high-density area between the Ogiri and Shiramizugoe areas. |