WGG Equation (Wyllie)
The WGG sonic porosity \phi_s equation is :
(1) | \frac{1}{V_{p \ log}} = \frac{1-\phi_s \ C_p}{V_{p \ m}} + \frac{\phi_s \ C_p}{V_{p \ f}} |
where C_p is compaction factor, accounting for the shaliness specifics and calculated as:
(2) | C_p = \frac{V_{shс}}{V_{sh}} |
where
V_{sh} – p-wave velocity for adjacent shales,
V_{shc} – p-wave velocity reference value for tight shales (usually 0.003 ft/μs).
GGG Equation (Gardner, Gardner, Gregory)
The GGG sonic porosity \phi_s equation is :
(3) | \frac{1}{V^{1/4}_{p \ log}} = \frac{(1-\phi_s)}{V^{1/4}_{p \ m}} + \frac{\phi_s}{V^{1/4}_{p \ f}} |
The above equation is based on the Gardner correlation for sonic density:
(4) | \rho_s = 171 \cdot V_{p \ m}^{1/4} |
where \rho_s is measured in \rm \big[ \frac{m^3}{kg} \big] and V_{p \ m} is measured in \rm \big[ \frac{m}{\mu s} \big]
and mass balance equation:
(5) | \rho_s = (1-\phi_s)\rho_m + \phi_s \rho_f |
RHG Equation (Raymer, Hunt, Gardner)
The RHG sonic porosity \phi_s equation is :
(6) | V_{p \ log} = (1-\phi_s)^2 V_{p \ m} + \phi_s V_{p \ f} |
and only valid for \phi_s < 0.37.