Development of high-accuracy geothermal reservoir model, considering the time-dependent behaviour of rock mass discontinuities

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K15493
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 31020:Earth resource engineering, Energy sciences-related
• Research Institution: Kumamoto University
• Principal Investigator: Sainoki Atsushi 熊本大学, 大学院先端科学研究部(工), 准教授 (70802049)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: 地下資源 / 誘発地震 / き裂性岩盤 / 地殻応力 / 拡張有限要素法 / 等価連続体モデル

Outline of Final Research Achievements

In this study, three study problems related to the development of high-accuracy geothermal reservoir model have been addressed. First, the method to simulate the heterogeneous stress distribution in a fractured rock mass has been developed. To achieve this, we employed the crack tensor model to simulate the metre-scale heterogeneity of stress state in the rock mass. Next, the simulation method that considers fluid leak-off from a rock discontinuity to the surrounding rock matrix has been developed in the framework of the finite element method. The method considers not only fluid flow in a macro-scale rock discontinuity but also fluid permeation to the surrounding rock mass with micro fractures. Finally, the stress state of discontinuity surface asperities was experimentally investigated on a micro scale by means of micro-focused X-ray CT and image analysis. Then, it was clarified that stress concentration locally takes place in the asperities.

Free Research Field

地下資源開発

Academic Significance and Societal Importance of the Research Achievements

き裂性岩盤内部の応力分布は極めて複雑であり、局所的な応力集中領域が点在していることが明らかとなった。この局所的な応力集中は、地熱貯留層や地下鉱山で生じる誘発地震と密接に関係している可能性が高く、誘発地震の高精度予測手法を開発する上で極めて重要になると考えられる。また、今回開発した拡張有限要素法をベースとした誘発地震シミュレーションコードにおいても、今後、水圧破砕や超臨界地熱発電など様々な分野への応用が期待される。最後に、不連続面表面アスペリティの微視的な応力状態は、不連続面の非線形挙動や時間依存性の水理特性変化を明らかにするための鍵になると考えられる。