Table 2. Hydro-gas model parameters for...

Table 2.

Hydro-gas model parameters for FEBEX

Equation	Parameter	Units	Symbol	FEBEX (intact)	Path I*	Path II*
van Genuchten retention curve	Capillary pressure	MPa	$P_{0}$	20	20	20
	Shape parameter in WRC	—	$ψ_{0}$	0.18	0.18	0.18
	Parameter in $P (ϕ)$	—	C	2	2	2
	Parameter in $λ (ϕ)$	—	D	4	4	4
Advective Darcy flux	Reference intrinsic permeability	m²	$k_{0}$	4 × 10⁻²¹	4 × 10⁻²¹	4 × 10⁻²¹
	Reference porosity	—	$ϕ_{0}$	0.44	0.44	0.44
	Initial porosity	—	ϕ	0.33	0.33	0.33
Gas relative permeability	Gas relative permeability – constant	—	A	100	100	100
	Gas relative permeability – power	—	n	3	3	3
Cubic law for permeability	Initial aperture to calculate a variable aperture	m	$b_{0}$	—	1 × 10⁻⁹	1 × 10⁻⁹
	Spacing of the fractures	m	a	—	1 × 10⁻⁵	4 × 10⁻⁵
	Reference strain to calculate aperture variations	—	$ε_{0}$	—	1 × 10⁻⁶	1 × 10⁻⁶
	Maximum aperture. Upper bound of aperture	m	$b_{\max}$	—	2 × 10⁻⁸	3 × 10⁻⁸
Diffusive Fick flux	Tortuosity coefficient	—	$τ$	0.8	0.8	0.8
	Diffusion coefficient**	m²/s	D	3 × 10⁻¹⁰	3 × 10⁻¹⁰	3 × 10⁻¹⁰

Equation	Parameter	Units	Symbol	FEBEX (intact)	Path I*	Path II*
van Genuchten retention curve	Capillary pressure	MPa	$P_{0}$	20	20	20
	Shape parameter in WRC	—	$ψ_{0}$	0.18	0.18	0.18
	Parameter in $P (ϕ)$	—	C	2	2	2
	Parameter in $λ (ϕ)$	—	D	4	4	4
Advective Darcy flux	Reference intrinsic permeability	m²	$k_{0}$	4 × 10⁻²¹	4 × 10⁻²¹	4 × 10⁻²¹
	Reference porosity	—	$ϕ_{0}$	0.44	0.44	0.44
	Initial porosity	—	ϕ	0.33	0.33	0.33
Gas relative permeability	Gas relative permeability – constant	—	A	100	100	100
	Gas relative permeability – power	—	n	3	3	3
Cubic law for permeability	Initial aperture to calculate a variable aperture	m	$b_{0}$	—	1 × 10⁻⁹	1 × 10⁻⁹
	Spacing of the fractures	m	a	—	1 × 10⁻⁵	4 × 10⁻⁵
	Reference strain to calculate aperture variations	—	$ε_{0}$	—	1 × 10⁻⁶	1 × 10⁻⁶
	Maximum aperture. Upper bound of aperture	m	$b_{\max}$	—	2 × 10⁻⁸	3 × 10⁻⁸
Diffusive Fick flux	Tortuosity coefficient	—	$τ$	0.8	0.8	0.8
	Diffusion coefficient**	m²/s	D	3 × 10⁻¹⁰	3 × 10⁻¹⁰	3 × 10⁻¹⁰

*Path I and ‘Unconnected Section I’ (Figure 3) have the same model parameters. Path II and ‘Unconnected Section II’ have the same model parameters. Intact clay refers to regions of the model domain where no advective flux of free gas occurs

**The diffusion coefficient was not measured directly, as the test focused on advective flow. The adopted value is representative – rather than being a measured value for FEBEX – and aligns with the magnitude of diffusion coefficients reported for comparable materials (Section 3.4)

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