Porosity (effective)

The rock volume  $//<![CDATA[ \begin{array}{l}\Omega_R\end{array} //]]>$ is split into three major components: effective pore volume  $//<![CDATA[ \begin{array}{l}\Omega_e\end{array} //]]>$, shale volume  $//<![CDATA[ \begin{array}{l}\Omega_{sh}\end{array} //]]>$ and rock martix  $//<![CDATA[ \begin{array}{l}\Omega_m\end{array} //]]>$:

The usual practice is to use relative volumes:

which are measured in V/V units (or fracs) and honor the following constraint:

The relative effective pore volume  $//<![CDATA[ \begin{array}{l}\phi_e\end{array} //]]>$ contains free or connate fluids (water, oil , gas) and called effective porosity.

It corresponds to air porosity of the dried laboratory cores:  $//<![CDATA[ \begin{array}{l}\phi_e = V_{\rm air \, core}\end{array} //]]>$.