Effective Porosity

Effective porosity, a dimensionless number, is the percentage of the total volume of a rock that is capable of transmitting fluids.  It is an important parameter in reservoir engineering and hydrogeology as it determines the capacity of a rock to store and transmit fluids such as oil, gas, or water.  Unlike total porosity, which includes all the pore spaces in a rock, effective porosity only considers the interconnected pore spaces that contribute to fluid flow.  Effective porosity is typically measured using core samples from the reservoir and analyzing them in a laboratory.  It can also be estimated from well logs and other indirect methods.  Effective porosity is usually lower than total porosity because not all pore spaces are interconnected or contribute to fluid flow. 

Factors that can Influence Effective Porosity

Grain Size and Sorting  -  Well-sorted sediments with uniform grain sizes tend to have higher effective porosity.
Cementation  -  The degree to which grains are bonded together can reduce the effective porosity.
Fracturing  -  Natural fractures in the rock can enhance the effective porosity by providing additional pathways for fluid flow.
Compaction  -  Over time, compaction can reduce the pore space and thus the effective porosity.

Effective Porosity formula
\( n_e \;=\;  V_{ep}  \;/\; V_b   \)
Symbol	English	Metric
\( n_e \) = Effective Porosity	\(dimensionless\)	\(dimensionless\)
\( V_{ep} \) = Effective Pore Volume	\(in^3\)	\(cm^3\)
\( V_b \) = Bulk Volume	\(in^3\)	\(cm^3\)