Tunnel and Underground Space (터널과지하공간)

Korean Society for Rock Mechanics and Rock Engineering (한국암반공학회)
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Coupled Hydro-Mechanical Modelling of Fault Reactivation Induced by Water Injection: DECOVALEX-2019 TASK B (Benchmark Model Test)

유체 주입에 의한 단층 재활성 해석기법 개발: 국제공동연구 DECOVALEX-2019 Task B(Benchmark Model Test)

  • Park, Jung-Wook (Geologic Environment Division, Korea Institute of Geoscience and Mining Resources) ;
  • Kim, Taehyun (Geologic Environment Division, Korea Institute of Geoscience and Mining Resources) ;
  • Park, Eui-Seob (Geologic Environment Division, Korea Institute of Geoscience and Mining Resources) ;
  • Lee, Changsoo (Radioactive Waste Disposal Research Division, Korea Atomic Energy Research Institute)
  • 박정욱 (한국지질자원연구원 지질환경연구본부) ;
  • 김태현 (한국지질자원연구원 지질환경연구본부) ;
  • 박의섭 (한국지질자원연구원 지질환경연구본부) ;
  • 이창수 (한국원자력연구원 방사성폐기물처분연구부)
  • Received : 2018.12.14
  • Accepted : 2018.12.21
  • Published : 2018.12.31
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Abstract

This study presents the research results of the BMT(Benchmark Model Test) simulations of the DECOVALEX-2019 project Task B. Task B named 'Fault slip modelling' is aiming at developing a numerical method to predict fault reactivation and the coupled hydro-mechanical behavior of fault. BMT scenario simulations of Task B were conducted to improve each numerical model of participating group by demonstrating the feasibility of reproducing the fault behavior induced by water injection. The BMT simulations consist of seven different conditions depending on injection pressure, fault properties and the hydro-mechanical coupling relations. TOUGH-FLAC simulator was used to reproduce the coupled hydro-mechanical process of fault slip. A coupling module to update the changes in hydrological properties and geometric features of the numerical mesh in the present study. We made modifications to the numerical model developed in Task B Step 1 to consider the changes in compressibility, Permeability and geometric features with hydraulic aperture of fault due to mechanical deformation. The effects of the storativity and transmissivity of the fault on the hydro-mechanical behavior such as the pressure distribution, injection rate, displacement and stress of the fault were examined, and the results of the previous step 1 simulation were updated using the modified numerical model. The simulation results indicate that the developed model can provide a reasonable prediction of the hydro-mechanical behavior related to fault reactivation. The numerical model will be enhanced by continuing interaction and collaboration with other research teams of DECOVALEX-2019 Task B and validated using the field experiment data in a further study.

본 논문에서는 국제공동연구 DECOVALEX-2019 프로젝트의 일환으로 수행된 Task B Benchmark Model Test(BMT)의 연구 결과를 소개하였다. Task B는 'Fault slip modelling'을 연구주제로 하며, 유체의 주입으로 인해 발생하는 단층의 재활성과 수리역학적 연계거동을 예측할 수 있는 해석기법을 개발하는 데에 목적이 있다. BMT 시나리오 해석은 각 참가팀들의 수치모델이 단층의 수리역학적 연동거동을 적절히 모사할 수 있는지 교차검증함으로써 각 해석코드의 완성도를 높이기 위하여 수행되었으며, 주입압 적용 조건, 단층 물성, 수리역학적 연동해석 조건 등에 따라 7개의 해석 모델로 이루어져 있다. 본 연구에서는 TOUGH-FLAC 연동해석 기법을 이용하여, 역학적 변형으로 야기되는 단층의 수리적 물성 변화와 간극의 기하학적 변화를 동시에 반영할 수 있는 수리역학적 커플링 모듈을 개발하였다. BMT 시나리오 해석을 위하여 Task B 1단계(Step 1) 연구에서 개발된 수치모델을 일부 수정하였고, 단층의 변형에 따른 압축률과 투수계수, 단층의 해석 메쉬의 변화가 해석에 반영될 수 있도록 하였다. 단층의 투수량계수와 저류계수가 단층 내 압력 분포, 주입수량, 변위, 응력 등 수리역학적 거동에 미치는 영향을 검토하였으며, 수정된 수치모델을 기수행된 1단계 연구에 적용하여 해석결과를 업데이트하였다. 해석 결과, 본 연구에서 개발한 해석기법이 물 주입으로 인한 단층의 거동을 합리적인 수준에서 재현할 수 있는 것으로 판단할 수 있었다. 본 연구의 해석모델은 Task B에 참여하는 국외 연구팀들과의 의견 교류와 워크숍을 통해 지속적으로 개선하는 한편, 향후 연구의 현장시험에 적용하여 타당성을 검증할 예정이다.

Keywords

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Fig. 1. Geometric information of BMT simulations and Step 1 models

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Fig. 2. Stepwise pressure injection scheme

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Fig. 3. Grid for host rock and interface for fault used in FLAC3D

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Fig. 4. Grid for fault used in TOUGH2 (initial mesh)

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Fig. 5. Coupled hydro-mechanical process and data transfer between TOUGH2 solid elements and FLAC3D interface nodes (after Park et al., 2018)

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Fig. 6. Pressure distributions estimated at 800 s of water injection (BMT1, BMT2 and BMT3)

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Fig. 7. Pressure distributions along the direction of the fault strike estimated at 200 s and 800 s of water injection (BMT1, BMT2 and BMT3)

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Fig. 8. Injection flow rate (BMT1, BMT2 and BMT3)

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Fig. 9. Pressure at the monitoring point P3 (BMT1, BMT2 and BMT3)

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Fig. 10. Effective normal stress at the injection P1(BMT1, BMT2 and BMT3)

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Fig. 11. Normal displacement along the direction of the fault strike estimated at 800 s of water injection (BMT1, BMT2 and BMT3)

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Fig. 12. Pressure distributions along the direction of the fault strike estimated at 200 s and 800 s of water injection (BMT4, BMT5,BMT6 and BMT7)

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Fig. 13. Injection flow rate (BMT4, BMT5, BMT6 and BMT7)

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Fig. 14. Pressure at P3 (BMT4, BMT5, BMT6 and BMT7)

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Fig. 15. Fault normal displacement along the direction of the fault strike estimated at 200 s and 800 s of water injection (BMT4 to BMT7)

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Fig. 16. Total normal stress, effective normal stress, shear stress and shear strength at P1 (BMT5 to BMT7)

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Fig. 17. Results of FM2 of Step 1 at 453 s of injection

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Fig. 18. Contour of displacement (FM2 of Step 1); the scaled arrow denotes the direction and magnitude of fault displacement at injection point P1.

Table 1. Numerical models of Task B participating teams

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Table 2. Material properties for Step 1 and BMT simulations

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Table 3. Descriptions of BMT simulations and updated information in hydro-mechanical coupling (α: compressibility, k: permeability)

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