[S-VC30] 火山の熱水系

[SVC30-01] Evaluation of aperture structure and fluid flow using numerical modeling in volcanic rocks stimulated by a chelating agent under geothermal conditions

*Luis Salala¹、Noriaki Watanabe¹、Noriyoshi Tsuchiya¹ (1.Graduate School of Environmental Studies, Tohoku University)

キーワード：EGS, Chelating agent, Permeability enhancement, Andesite, Selective dissolution of minerals

Enhanced geothermal systems (EGS) are recognized as a viable renewable energy source in areas with high geothermal temperatures. Nevertheless, geothermal reservoirs can experience reduced permeability during exploration or operation. Research on chelating agents in geothermal environments is widespread as a complementary method to conventional methods such as hydraulic and chemical stimulation. Previous studies have reported rapid and significant improvements in the permeability of granitic and volcanic rocks using aqueous solutions of glutamic acid-L-diacetic acid (GLDA) under acidic (Watanabe et al., 2021; Salalá et al., 2023) and alkaline conditions (Takahashi et al., 2023). However, clearance about how the formation of voids due to selective mineral dissolution influences permeability enhancement still needs to be studied. Furthermore, the optimal time of chelating agent solution injection still needs to be determined. In this study, we conducted several simulations using a 2D fracture model, the mode of minerals of an andesitic rock, and the rate of dissolution of minerals by GLDA aqueous solution at pH 4 and 10 to observe the permeability evolution of volcanic rock. The study results were consistent with those obtained experimentally, where rapid enhancement of permeability by GLDA solution injection is obtained in the first 20 minutes of injection for the acidic condition and in the first 5 minutes for the alkaline conditions. This simulation allowed us to understand the development of the fluid flow path and how this is better improved at alkaline conditions, where the connectivity of voids created by the selective dissolution of the groundmass allows to enhance the permeability better. This numerical modeling can be the starting point to simulate the permeability enhancement behavior due to the injection of GLDA as a function of the mode of minerals, applying it to predict the behavior of GLDA chemical stimulation to other kinds of volcanic rocks.

Keywords: EGS, chelating agent, permeability enhancement, andesite, selective dissolution of minerals.

Watanabe et al., 2021. Scientific Reports 11. https://doi.org/10.1038/s41598-021-99511-6
Salalá et al., 2023. Geothermics 107. https://doi.org/10.1016/j.geothermics.2022.102586
Takahashi et al., 2023. Geothermics 109. https://doi.org/10.1016/j.geothermics.2022.10264