Development of coupled numerical simulator for describing processes within rocks from fracture generation to long-term change of fracture permeability

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K14826
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 22030:Geotechnical engineering-related
• Research Institution: Osaka University
• Principal Investigator: Ogata Sho 大阪大学, 大学院工学研究科, 助教 (50868388)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 岩盤内亀裂 / 透水特性 / 化学現象 / 連成数値シミュレータ / 高レベル放射性廃棄物地層処分 / 亀裂の内部構造

Outline of Final Research Achievements

We attempted to develop a coupled simulator that can solve the entire process from the rock fracture generation to the subsequent reaction-driven permeability change. First, a constitutive model that can predict the ratio of fracture contact area, which is an important parameter in the calculation of geochemical reaction in a fracture, was constructed, and its validity was verified through comparison with results of mechanical tests. Then, a new coupled simulator was developed by integrating above-mentioned constitutive model with a fracturing analysis model and a coupled model including geochemical reactions. Finally, a proposed simulator was applied to long-term prediction assuming the geological disposal of high-level radioactive waste. Predicted results showed that after numerous fractures were generated during excavation, the pressure dissolution occurred within the generated fractures, resulting in a long-term reduction in permeability.

Free Research Field

岩盤工学、地盤工学、資源工学

Academic Significance and Societal Importance of the Research Achievements

本研究で構築した連成数値シミュレータによって、岩盤内に新たに生成された亀裂が辿る一連の素過程（生成～経年変化）を計算機上ではじめて一気通貫に表現できるようになる。その結果、地層処分や地熱発電といった、初期施工時に新たな亀裂の生成を伴う種々の地下開発事業における岩盤の透水特性を従来より格段に精度よく予測可能となる。これにより、高レベル放射性廃棄物地層処分施設の物質閉じ込め性能や地熱貯留層における地熱流体回収性能等を時系列で定量評価可能となり、地層処分技術の安全性や地熱発電の生産性の更なる向上に貢献し得ると考えられる。