[A-HW23] Isotope Hydrology 2023

[AHW23-01] Residence time estimation of geothermal fluids using environmental tracers

★Invited Papers

*Koki Kashiwaya¹, Ikuya Inukai², Ikuto Sakai¹, Yohei Tada¹, Kensuke Matsumoto³, Hiroyuki Matsuzaki⁴, Katsuaki Koike¹ (1.Graduate School of Engineering, Kyoto University, 2.Graduate School of Engineering, Kyoto University (Former affiliation), 3.Okuaizu Geothermal Co., Ltd, 4.The University Museum, The University of Tokyo)

Keywords:Geothermal fluid, Residence time, Environmental tracer

Against climate change caused by global warming, many countries, including Japan, aim to achieve carbon neutrality by 2050. Under such circumstances, the promotion of renewable energy utilization is required. Geothermal energy is a type of renewable energy. Japan's geothermal resources, estimated by Muraoka et al. (2008) to be 23.47 GW, are among the three largest in the world. Geothermal power generation is a representative form of geothermal energy utilization. Imamura et al. (2016) estimated that geothermal power generation emits less carbon dioxide, a typical greenhouse gas, over its life cycle than other power generation methods, such as wind, solar, and nuclear. Therefore, further utilization of geothermal power generation can contribute to reducing carbon dioxide emissions. In geothermal power generation, geothermal fluid is extracted from an underground geothermal reservoir that contains high-temperature geothermal fluid to the surface through wells and returned underground after being used for power generation. The steam volume and reservoir temperature must be maintained for sustainable geothermal power generation. However, the steam volume may drop after the start of geothermal power generation, making sustainable power generation difficult. Geothermal fluid is the medium that carries heat in a geothermal system. Information on the origin, recharge and circulation conditions of geothermal fluid, especially the speed of circulation, is important to consider the sustainable utilization of geothermal energy. From this viewpoint, the authors have been applying environmental tracers to estimate the residence time of geothermal fluids. In this presentation, we will review the environmental tracers used to estimate the residence time of groundwater containing geothermal fluid, introduce examples of application in geothermal areas in Indonesia and Fukushima Prefecture, and discuss how environmental tracers can be used to estimate the residence time of geothermal fluid.

References
Imamura, E., Iuchi, M., Bando, S. (2016) Comprehensive assessment of life cycle CO₂ emissions from power generation technologies in Japan. CRIEPI Report, Y06.
Muraoka, H., Sakaguchi, K., Komazawa, M. (2008) Assessment of hydrothermal resource potentials in Japan 2008. The Journal of the Geothermal Research Society of Japan, 30, Supplement, B01.