Density Channel to Velocity Conversion

Use the option Database Tools > Database Utilities > Convert Density to Velocity, (geogxnet.dll(Geosoft.GX.VelocityToDensity.DensityToVelocity;Run)*), to convert a channel containing rock densities into seismic velocities using one of several published methods. The option is also available in the GM-SYS Profile Modelling extension.

Convert Density Channel to Velocity dialog options

Input density channel	Select the name of the existing channel containing density values to be converted. Script Parameter: DEN2VEL.CHANNELINPUT
Density units	Select the density units the values in the input channel represent. Script Parameter: DEN2VEL.UNITSINPUT
Output velocity channel	Select the name of the new or existing channel that will contain the calculated velocity values. Script Parameter: DEN2VEL.CHANNELOUTPUT
Velocity units	Select the velocity units for the calculated velocities. Script Parameter: DEN2VEL.UNITSOUTPUT
Method	Select the conversion method from the list. Script Parameter: DEN2VEL.METHOD
Dummy outside range	Each conversion method is defined within a range of velocities (and corresponding densities). Check this box if you wish to dummy calculated values that fall outside of the defined range. Script Parameter: DEN2VEL.DUMMY

Application Notes

Published empirical relationships between seismic velocity and bulk density of various rock types are commonly used in processing seismic data (Gardner et al., 1974; Brocher, 2005).  The Convert Velocity Channel to Density GX and Convert Density Channel to Velocity GX utilize 5th order polynomial expansions to approximate several of these relationships to less than 0.001 g/cm³ variance.  Velocity to Density function and the inverse Density to Velocity function should match to within 4 significant figures.

Additional Methods

We have implemented Gardner, Nafe-Drake, and some other conversions as 5th order polynomial functions. The method names, coefficients, and appropriate velocity ranges are stored in the vel_density.csv file in the Oasis montaj distribution. Coeffients for Nafe-Drake, Christensen & Mooney, and Godfrey et al. methods are adapted from Brocher (2005). "Gardner" methods use coeffients derived from the tables in Gardner et al., 1974.

Additional Velocity-to-Density conversion functions may be added by editing the %USERPROFILE%\Documents\Geosoft\Desktop Applications \csv\vel_density.csv file. The conversion must be represented by a 5th order or lower polynomial, as described in the file header.  Coefficients are appropriate for Velocity units of m/s and Density units of g/cm³ and unit conversions are performed by the GXs.

References