Hydraulic-Mechanical Modeling on Fracture Transmissivity Evolution Around a Borehole

Chae-Soon Choi; Kyung-Woo Park; Byeong-Hak Park; Nak-Youl Ko; Sung-Hoon Ji

doi:10.9720/kseg.2021.1.055

All Issue

2021 Vol.31, Issue 1 Preview Page Next Page

Research Article

Hydraulic-Mechanical Modeling on Fracture Transmissivity Evolution Around a Borehole 시추공 주변 단열 투수도 진화에 대한 수리-역학 연동 모델링 평가

31 March 2021. pp. 55-66

PDF XML

Abstract

Hydraulic-mechanical (H-M) coupled numerical modeling was used to evaluate the evolution of hydrogeological properties in response to the installation and expansion of a borehole. A domain with a discrete fracture network was adopted for discontinuum modeling to simulate changes in fracture apertures. Comparison with real hydraulic test data shows that the effects of principal stress direction and expansion of borehole diameter were reasonably simulated by H-M coupled numerical modeling. The modeling confirmed that aperture changes depended on the principal stress direction, with an increase in aperture size due to vertical displacement being the dominant effect. A concentration of shear dilation around the borehole had an additional, subsidiary, effect on the hydrogeological evolution. These results show that the permeability of fractured rock can be increased by changing the hydraulic properties of a fracture through stress redistribution caused by the installation and expansion of a borehole.

Keywords

discrete fracture network

discontinuum modeling

vicinity of borehole

aperture change

본 연구에서는 방사성폐기물 처분 시 천연방벽의 수리 특성 진화와 관련하여, 시추공 설치 및 확공이 결정질 암반 내 단열 및 수리 특성에 영향을 미칠 가능성을 평가하기 위해 수리-역학 연동 수치해석을 수행했다. 시추공 부근에서의 간극 열림과 투수성 변화 여부를 평가하기 위해 단열망을 기반으로 한 불연속체 해석 도메인을 이용했다. 단열암반에서의 현장수리시험 모사를 통해 주응력방향과 시추공 직경 변화의 영향을 평가하였다. 먼저 단열의 간극변화가 주응력방향에 의존함을 확인했다. 그리고 수직변위에 의한 간극크기 증가가 지배적이었다. 시추공 부근에 전단팽창이 집중되는 것도 단열의 수리지질학적 진화에 영향을 미칠 수 있음을 알 수 있었다. 수치해석 결과는 시추공 설치 및 확공에 따른 응력교란에 의해 단열 특성이 변화하여 단열 암반의 투수성이 증가할 수 있다는 것을 보여준다. 추후 본 연구모델을 기반으로 실제 크기의 처분공 주변에서의 정확한 수리적 변화를 분석하기 위해서는 3차원 해석모델로 보완되어야 할 것으로 판단되었다.

키워드

단열망

불연속체해석

시추공 주변

간극변화

References

Agheshlui, H., Sedaghat, M.H., Matthai, S., 2018, Stress influence on fracture aperture and permeability of fragmented rocks, Journal of Geophysical Research: Solid Earth, 123(5), 3578-3592. 10.1029/2017JB015365

Baghbanan, A., Jing, L., 2008, Stress effects on permeability in a fractured rock mass with correlated fracture length and aperture, International Journal of Rock Mechanics and Mining Sciences, 45(8), 1320-1334. 10.1016/j.ijrmms.2008.01.015

Barton, N., Choubey, V., 1977, The shear strength of rock joints in theory and practice, Rock Mechanics and Rock Engineering, 10(1-2), 1-54. 10.1007/BF01261801

Chang, K.M., Lee, E.Y., Kim, C.L., Rhee, C.G., Kim, H.J., 2000, Estimation of conductivity tensor of fractured rocks from single-hole packer test, The Journal of Engineering Geology, 10(1), 13-25 (in Korean with English abstract).

Cho, H., Cheong, J.Y., Lim, D.H., Hamm, S.Y., 2017, Quantification of heterogenous background fractures in bedrocks of Gyeongju LILW disposal site, The Journal of Engineering Geology, 27(4), 463-474 (in Korean with English abstract).

Fox, A., Forchhammer, K., Pettersson, A., La Pointe, P., Lim, D.H., 2012, Geological discrete fracture network model for the Olkiluoto site, Eurajoki, Finland, Version 2.0; POSIVA 2012-27, POSIVA OY, Eurajoki, Finland.

Hartley, L., Hoek, J., Swan, D., Roberts, D., Joyce, S., Follin, S., 2009, Development of a hydrogeological discrete frcture network model for the Olkiluoto site descriptive model 2008; Working report 2009-61, POSIVA OY, Eurajoki, Finland.

Ji, S.H., Park, K.W., Lim, D.H., Kim, C., Kim, K.S., Dershowitz, W., 2012, A hybrid modeling approach to evaluate the groundwater flow system at the low- and intermediate-level radioactive waste disposal site in Gyeong-Ju, Korea, Hydrogeology Journal, 20(7), 1341-1353. 10.1007/s10040-012-0875-x

Jo, Y., Chang, C., Park, K.W., Ji, S.H., Lee, C., 2017, In situ stress estimation in KURT site, Journal of the Geological Society of Korea, 53(5), 689-701 (in Korean with English abstract). 10.14770/jgsk.2017.53.5.689

Lee, C., Yoon, S., Cho, W.J., Jo, Y., Lee, S., Jeon, S., Kim, G.Y., 2019, Study on thermal, hydraulic, and mechanical properties of KURT granite and Gyeongju bentonite, Journal of the Nuclear Fuel Cycle and Waste Technology, 17(S), 65-80 (in Korean with English abstract). 10.7733/jnfcwt.2019.17.S.65

Lim, D.H., 2002, Mass transport analysis in the near field of geologic repository, Ph.D. Dissertation, Department of Nuclear Engineering, University of California, Berkeley, 13-20.

Min, K.B., Rutqvist, C.F., Tsang, C.F., Jing, L., 2004, Stress-dependent permeability of fractured rock masses: a numerical study, International Journal of Rock Mechanics and Mining Sciences, 41(7), 1191-1210. 10.1016/j.ijrmms.2004.05.005

Park, K.W., Kim, K.S., Koh, Y.K., Choi, J.W., 2011, Synthetic study on the geological and hydrogeological model around KURT, Journal of the Korean Radioactive Waste Society, 9(1), 13-21 (in Korean with English abstract). 10.7733/jkrws.2011.9.1.13

Park, K.W., Ko, N.Y., Ji, S.H., 2019, Assesement of hydrogeological characteristics at BDZ-1 borehole in KAERI underground research tunnel, KAERI/TR-7750/2019, Daejeon, Korea.

Park, K.W., Ko, N.Y., Ji, S.H., 2020b, A study on the applicability of the hydraulic test method performed at an underground research facility in crystalline rock, Economic and Environmental Geology, 53(2), 121-131 (in Korean with English abstract)

Park, K.W., Park, B.H., Ko, N.Y., Ji, S.H., 2020a, Applicability of pulse tests to estimate transmissivity in crystalline rock, The Journal of Engineering Geology, 30(3), 223-235 (in Korean with English abstract).

Park, S., Kim, K.I., Kwon, S., Yoo, H., Xie, L., Min, K.B., Kim, K.Y., 2018, Development of a hydraulic stimulation simulator toolbox for enhanced geothermal system design, Renewable Energy, 118, 879-895. 10.1016/j.renene.2017.11.016

Synn, J.H., Park, C., Lee, B.J., 2013, Regional distribution pattern and geo-historical transition of in-situ stress fields in the Korean peninsula, Tunnel and Underground Space, 23(6), 457-469 (in Korean with English abstract). 10.7474/TUS.2013.23.6.457

Information

Publisher :Korean Society of Engineering Geology
Publisher(Ko) :대한지질공학회
Journal Title :The Journal of Engineering Geology
Journal Title(Ko) :지질공학
Volume : 31
No :1
Pages :55-66
Received Date : 2021-02-04
Accepted Date : 2021-03-09
DOI :https://doi.org/10.9720/kseg.2021.1.055

The Journal of Engineering Geology ISSN:1226-5268(Print) 2287-7169(Online) 지질공학

All Issue