Compressibility of single-phase fluid with density $\begin{array}{l}\rho_f\end{array}$ and molar volume $\begin{array}{l}V_{mf}\end{array}$ :

(1)	$\begin{array}{l}\displaystyle c_f = \frac{1}{\rho_f} \frac{\partial \rho_f}{\partial p} = -\frac{1}{V_{mf}} \frac{\partial V_{mf}}{\partial p}\end{array}$

This can be redefined in terms of fluid volume $\begin{array}{l}V_f\end{array}$ :

Symbol	Dimension	SI units	Oil metric units	Oil field units
$\begin{array}{l}c_f\end{array}$	M^-1 L¹T²	Pa^-1	kPa^-1	psi^-1

The multi-phase compressibility is a simple sum of its components.

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See also