Effective porosity (${\varphi }_e$)

Effective porosity is the pore-volume fraction accessible to connected transport under the specified measurement or model. It excludes isolated pore volume and may also exclude poorly exchanging regions on the transport timescale, so $0\le {\varphi }_e\le \varphi$ for total porosity $\varphi$. In a simple mobile-volume model the mean pore velocity is $q/{\varphi }_e$; the assumptions behind that model matter when interpreting tracer arrival times. A sample with total porosity $0.25$ but mobile pore fraction $0.20$ and Darcy flux $2.0\times 10^{-5}\mathrm{m}{\mathrm{s}}^{-1}$ has mobile mean pore velocity $1.0\times 10^{-4}\mathrm{m}{\mathrm{s}}^{-1}$. Woessner and Poeter discuss the role of connectivity and slowly exchanging pores.^[ref]