Compressibility of multiphase fluid in thermodynamic equilibrium at a given pressure p and temperature T is a simple sum of its single-phase components:
(1) | c_f(p, T) = \sum_{\alpha} s_\alpha \cdot c_\alpha(p,T) |
where
s_\alpha | \alpha-phase saturation, subjected to \sum_{\alpha} s_\alpha = 1 |
---|---|
c_\alpha(p, T) | \alpha-phase compressibility as function of pressure p and temperature T |
In most popular practical case of a 3-phase fluid model this will be:
(2) | c_f = s_w \, c_w + s_o \, c_o + s_g \, c_g |
where \{ w, \, o, \, g \} mean water phase, oil phase and gas phase.
Some applications (like multi-phase pressure diffusion) account for the impact of phase exchange on the total compressibility which require some corrections to equation
(2):
(3) | c_t(s,P) = c_r + c_w s_w + c_o s_o + c_g s_g + s_o [ R_{sp} + (c_r + c_o) R_{sn} ] + s_g [ R_{vp} + R_{vn}(c_r + c_g) ] |
See Non-linear multi-phase pressure diffusion @model for derivation of (3).
See also
[Multi-phase pressure diffusion][Compressibility] [Single-phase fluid compressibility]