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Sequential Methods for Coupled Geomechanics and Multiphase Flow

Sequential Methods for Coupled Geomechanics and Multiphase Flow

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B.5. δφ FOR SINGLE-PHASE FLOW 231<br />

B.5 δφ <strong>for</strong> single-phase flow<br />

We derive the expression of δφ based on Geertsma (1957)’s work, where p is the fluid tension.<br />

Note that p in this thesis is the fluid pressure. We denote by Vp <strong>and</strong> Vb the pore <strong>and</strong> bulk<br />

volumes, respectively. Then the change of Vp with respect to the movement of the solid<br />

skeleton is expressed as<br />

which yields<br />

δVp<br />

Vp<br />

=<br />

<br />

1<br />

Vp<br />

∂Vp<br />

∂p<br />

δVp = ∂Vp<br />

∂p<br />

<br />

<br />

<br />

σv<br />

− 1<br />

Vp<br />

<br />

<br />

<br />

σv<br />

δp + ∂Vp<br />

<br />

<br />

<br />

∂σv<br />

p<br />

p<br />

<br />

∂Vp <br />

δp +<br />

∂σv<br />

1<br />

Vp<br />

δσv, (B.19)<br />

<br />

∂Vp <br />

<br />

∂σv<br />

p<br />

(δσv + δp). (B.20)<br />

Similarly, the change of Vb with respect to the movement of the solid skeleton is described<br />

as<br />

which yields<br />

δVb<br />

Vb<br />

=<br />

<br />

1<br />

Vb<br />

∂Vb<br />

∂p<br />

δVb = ∂Vb<br />

∂p<br />

<br />

<br />

<br />

σv<br />

− 1<br />

Vb<br />

<br />

<br />

<br />

σv<br />

δp + ∂Vb<br />

<br />

<br />

<br />

∂σv<br />

p<br />

p<br />

<br />

∂Vb <br />

δp +<br />

∂σv<br />

1<br />

Vb<br />

δσv, (B.21)<br />

<br />

∂Vb <br />

<br />

∂σv<br />

p<br />

(δσv + δp). (B.22)<br />

Under the condition that δσv + δp = 0, we obtain <strong>for</strong> the dilation of the solid grains<br />

δVp<br />

Vp<br />

= δVb<br />

Vb<br />

= − 1<br />

δp =<br />

Ks<br />

1<br />

δσv, (B.23)<br />

Ks<br />

where Ks is the stiffness of the solid grains. Since the drained bulk modulus Kdr is defined<br />

as<br />

1<br />

Vb<br />

<br />

∂Vb <br />

<br />

∂σv<br />

p<br />

= 1<br />

, (B.24)<br />

Kdr

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