A pore volume $\begin{array}{l}\Omega_\phi\end{array}$ fraction of bulk rock volume $\begin{array}{l}\Omega_r\end{array}$ containing the hydrodynamically connected fluids (also called free fluids) within each pore element:

$\begin{array}{l}\displaystyle \phi_e = V_\phi = \frac{\Omega_\phi}{\Omega_r}\end{array}$

It splits into two components: open porosity and closed porosity:

$\begin{array}{l}\displaystyle \phi_e = V_{\rm open} + V_{\rm closed}\end{array}$

The log name is PHIE.

Effective porosity is a function of reservoir pressure at a given location $\begin{array}{l}p({\bf r})\end{array}$

(1)	$\begin{array}{l}\displaystyle \phi(\mathbf{r}, \ p) = \phi_0(\mathbf{r}) \exp \left[ - \int_{p_i}^p c_r(p) \, dp \right]\end{array}$

where

$\begin{array}{l}c_r(p)\end{array}$	pore compressibility
$\begin{array}{l}p_i\end{array}$	initial formation pressure

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See also