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Part of the bulk rock volume containing the hydrodynamically connected fluids called free fluids.

The log name is PHIE

Although the fluid inside the pore is movable but some pores maybe isolated from each other and do not contribute to rock permeability

See also

A pore volume 

\phi_e  = \frac{V_\phi}{V_r}

The log name is PHIE.

The reason to introduce this concept is that a part of the actual inter-grain void is filled with shale thus reducing the actual volume available for fluids.

It splits into two components:

subject to condition:

\phi_e = \phi_{\rm opn} + \phi_{\rm cls}

 
Effective porosity is a function of reservoir pressure at a given location

\phi_e(\mathbf{r}, \ p) = \phi_{ei}(\mathbf{r}) \exp \left[ \int_{p_i}^p c_\phi(p) \, dp \right]

where

This leads to the effect of Porosity Shrinkage.

Since the pore compressibility is very low (~ c_ϕ  = 0.5 ÷ 1.5  GPa^-1) and has a weak dependence on  reservoir pressure  for subsurface rocks in petroleum reservoirs the 

\phi_e(\mathbf{r}, \ p) = \phi_{ei}(\mathbf{r}) \cdot \left[ 1 + c_\phi \, (p-p_i) + 0.5 \, c_\phi^2 \, (p-p_i)^2 \right]

Most Subsurface E&P Disciplines (except Petrophysics) usually omit index "_e" and denote Effective porosity as 

See also

...

Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petrophysics (PP) / Volumetric Rock Model

[ Basic reservoir properties ] [ Pore volume ] [ Connected pore volume ] [ Closed pore volume ] [ Porosity ] [ Open porosity ] [ Closed porosity ][ Initial Porosity ϕ_i ]

[ Pore compressibility @model ]Volumetric Rock Model