Abstract
The effect of hydro-mechanical (HM) coupling on the hydraulic properties of the fractured rock mass was investigated for unidirectional and radial flow configurations by numerical simulation, theoretical analysis and practical verification. The discrete element method was used to numerically investigate the effect of HM coupling on the hydraulic properties of the fractured rock mass. The representative elementary volume (REV) size for radial flow configuration (RFC) is smaller than that for unidirectional flow configuration (UFC). But the REV size first decreases and then increases as the lateral stress coefficient increases from 0.333 to 3 for both RFC and UFC. The effect of HM coupling induces the aperture increase and thus an increase in the permeability. The apertures of fracture sets were found to jointly dominate the permeability in UFC, whereas the minimum apertures of the fracture sets dominate the permeability in RFC under HM coupling. Analytical solutions for the permeability of fractured rock masses were developed in RFC and UFC. The analytical solution in RFC was verified against the results of field injection tests conducted in an underground oil storage caverns. Using the solution, two limits for the scattered permeability coefficients of the fractured rock mass were obtained in field injection tests with consideration of the HM coupling. The aperture change with the elevated injection pressure was calculated, and the used to explain observations of on the variation in the permeability coefficient with the injection pressure.
Article Highlights
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The effect of HM coupling on the hydraulic properties was investigated for radial and unidirectional flow configurations.
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REV sizes decreased firstly and then increased with the lateral stress coefficient.
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The permeability coefficients increased firstly and then decreased with the lateral stress coefficient.
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Analytical solutions to permeability subjected to HM coupling were developed.
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The solutions were verified against field observations on the permeability.
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- A :
-
Section area
- b :
-
Fracture aperture
- b 0 :
-
Initial fracture aperture
- d :
-
The width of block intersected
- e r, e θ :
-
Unit vectors in polar coordinate system
- F f :
-
Force on a fracture exerted by fluid
- Δh :
-
Difference in water heads
- g :
-
Gravity acceleration
- i, j :
-
Unit vectors in rectangular coordinate system
- J r, J θ :
-
Hydraulic gradient radial and tangential directions
- k :
-
Fracture permeability coefficient
- K :
-
Permeability tensor
- k e :
-
Permeability coefficient of rock mass with a set of fractures
- k r :
-
Equivalent permeability coefficient in RFC
- k u :
-
Equivalent permeability coefficient in UFC
- K n :
-
Fracture normal stiffness
- L 1 :
-
Length of flow
- L f :
-
Length of fracture
- p :
-
Fluid pressure
- p 1, p 2 :
-
Fluid pressure at the two ends of the fracture
- Δp :
-
Fluid pressure drop
- q :
-
Flow rate
- q r, q θ :
-
Flow rate in radial and tangential directions, respectively
- Q :
-
Flow rate
- r 1 :
-
Radius of a surface
- r i :
-
Radius of the inner boundary
- r e :
-
Radius of the outer boundary
- s i :
-
Joint spacing
- u n :
-
Fracture normal displacement
- V r, V θ :
-
Flow velocities in radial and tangential directions, respectively
- σ n :
-
Fracture normal stress
- τ :
-
Fracture shear stress
- λ :
-
Lateral stress coefficient
- ρ w :
-
Fluid density
- ν w :
-
Coefficient of kinematic viscosity
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Acknowledgements
This study was financially supported by the National Natural Science Foundation of China with No. 51779045, Liao Ning Revitalization Talents Program with No. XLYC1807029, the Fundamental Research Funds for the Central Universities with Nos. N2001026, N2001025 and N2101005, Liaoning Natural Science Foundation with Nos. 2019-MS-114 and 2019-YQ-02.
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Li, W., Wang, Z., Qiao, L. et al. The effects of hydro-mechanical coupling on hydraulic properties of fractured rock mass in unidirectional and radial flow configurations. Geomech. Geophys. Geo-energ. Geo-resour. 7, 87 (2021). https://doi.org/10.1007/s40948-021-00286-x
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DOI: https://doi.org/10.1007/s40948-021-00286-x