# Mass balance equation

${\displaystyle \rho =\phi \rho _{\mathrm {f} }+(1-\phi )\rho _{\mathrm {m} }\ }$
where ${\displaystyle \phi }$ is the total porosity, ${\displaystyle \rho }$ is the measured bulk density, ${\displaystyle \rho _{\mathrm {m} }}$ is the density of the rock matrix, and ${\displaystyle \rho _{\mathrm {f} }}$ is the density of the saturating fluid.