[A-HW24] Isotope Hydrology 2024

[AHW24-P08] Effectiveness of independent component analysis in elucidating hydrochemical evolution processes of geothermal fluids

*Koki Kashiwaya¹, Katsuaki Koike¹ (1.Graduate School of Engineering, Kyoto University)

Keywords:geothermal fluid, groundwater, hydrochemical evolution, independent component analysis

With the need to reduce greenhouse gas emissions as a countermeasure against climate change, further utilization of geothermal energy is expected because of its advantages, such as low CO₂ emissions and stable power output. Many forms of geothermal energy use, including geothermal power generation, utilize the heat of geothermal fluid. Therefore, it is necessary to prevent the depletion of geothermal fluid for sustainable use of geothermal energy, and it is important to estimate the circulation regimes of geothermal fluid, such as how water is recharged and flows in a geothermal system. Geochemical properties of geothermal fluids, including isotopic compositions, are useful for estimating the circulation regimes of geothermal fluids because they depend on the origins of geothermal fluids and processes experienced by geothermal fluids, such as mixing of water from different origins, water-rock reactions with rocks distributed along the flow path, phase transformation of water, and so on. The authors have focused on Independent Component Analysis (ICA), a type of unsupervised learning method, for extracting information on the processes experienced by geothermal fluids from geochemical data obtained in analyses of geothermal fluid samples. In previous studies by the authors, it has been implied that the compositions of water before mixing can be estimated by applying ICA to the concentration data of mixed water samples. However, whether ICA can identify processes other than mixing has not been examined. In this presentation, concentration data are generated with known hydrochemical evolution processes using a geochemical modeling code PHREEQC, and independent component analysis is applied to them to estimate the hydrochemical evolution processes. Based on the results, the effectiveness of independent component analysis in elucidating the hydrochemical evolution processes of groundwater and geothermal fluids is discussed.