Dictionary:Gardner’s equation

Term	Gardner's equation
Pronunciation	gard’ n∂r
Series	Geophysical Reference Series
Author	Robert E. Sheriff
DOI	http://dx.doi.org/10.1190/1.9781560802969
ISBN	978-1-56080-118-4
Store	SEG Online Store

Gardner's equation, or Gardner's relation, named after G. H. F. Gardner and L. W. Gardner, is an empirically derived equation that relates seismic P-wave velocity to the bulk density of the lithology in which the wave travels. The equation reads:

$\rho =\alpha V_{p}^{\beta }$

where $\rho$ is bulk density given in g/cm³, $V_{p}$ is P-wave velocity given in ft/s, and $\alpha$ and $\beta$ are empirically derived constants that depend on the geology. Gardner et al. proposed that one can obtain a good fit by taking $\alpha =0.23$ and $\beta =0.25$. Assuming this, the equation is reduced to:

$\rho =0.23V_{p}^{0.25}.$

If $V_{p}$ is measured in m/s, $\alpha =0.31$ and the equation is:

$\rho =0.31V_{p}^{0.25}.$

This equation is very popular in petroleum exploration because it can provide information about the lithology from interval velocities obtained from seismic data. The constants $\alpha$ and $\beta$ are usually calibrated from sonic and density well log information but in the absence of these, Gardner's constants are a good approximation.

The empirical relationship that density is proportional to the 1/4 power of P-wave velocity:

$\rho =aV_{\mathrm {P} }^{\frac {1}{4}},$

where a is 0.31 when V is in m/s, 0.23 when in ft/s.