[S-VC35] Hydrothermal systems of volcanoes

[SVC35-P03] Development of a numerical simulator for non-isothermal multiphase fluid flow with silica reactive transport processes in magmatic hydrothermal systems

*Norihiro Watanabe¹, Yasuo Matsunaga¹, Atsushi Okamoto², Noriyoshi Tsuchiya², Masaoki Uno², Takashi Akatsuka³, Tatsuya Kajiwara³, Hanae Saishu¹, Takuya Ishibashi¹, Yusuke Yamaya¹, Hiroshi Asanuma¹ (1.National Institute of Advanced Industrial Science and Technology, 2.Graduate School of Environmental Studies, Tohoku University, 3.Geothermal Engineering Co., Ltd.)

Supercritical geothermal reservoirs, which are estimated to exist at depths of 3 to 5 km beneath volcanic and geothermal areas in Japan, are expected as a next-generation geothermal resource. Previous studies have suggested that these reservoirs may be composed of ultrahigh-temperature, high-pressure fluids (equivalent to or above the critical point of water) stored beneath silica-sealing layers. However, the existence of the layer has not yet been confirmed through drilling. In addition, the formation mechanism of the layer is still unknown. Hence, better understanding of the silica seal layer is one of the important issues for the exploration of supercritical geothermal resources. In this study, we developed a numerical simulator that can take into account heat, fluid, and silica reaction transport in magmatic hydrothermal systems to investigate the possibility that silica seal layers can be formed by magmatic hydrothermal activity. The simulator can handle temperatures up to about 800°C and pressures up to 500 MPa. The simulator models magmatic water as salinewater (H₂O-NaCl) and can support single-phase, gas-liquid two-phase, and gas-liquid-solid three-phase states as fluid states. Currently, only the quartz-salinewater reaction is considered in the reactive transport. In the presentation, using the developed simulator, we will discuss the fluid state change, silica precipitation behavior during magmatic fluid ascending, and the influence of subsurface temperature and pressure conditions on the behavior.