A module based on log input; the Cross-Plot module allows pairs of Elastic Parameters to be selected for display. Certain pairs are defined for selection, but you can also select your own pairing – including petrophysical logs to find a relationship between elastic logs and any petrophysical log.
Each point represents one sample from the logs and a third log can also be selected as the colour bar adding further detail to the plot. Data is automatically resampled in the depth domain to 0.25m. If you wish to display a cross-plot in the time domain the default sample rate can be changed from between 1-20 with the frequency max able to be adjusted between 1-125Hz.
Polygons can be drawn on the cross plot to isolate the lithology or fluid target you are aiming to determine. Gas sand, for example, can be clearly separated from background shale in an AI vs PR cross plot.
The display can be in linear or log. If the linear fit is selected it will be displayed on the plot and the values of the linear regression shown including the Goodness of Fit (GOF) and the Mudrock or Gardners Rule will be displayed on the appropriately selected cross plot (Vp vs Vs and Vp vs Rhob, respectively).
The plot will display the robust regression linear fit if selected and the Mudrock line if the plot is Vp vs Vs. Gardners Rule will be shown if the plot is Vp vs Rho in the Log Scale.
Mudrock line – In rock physics and petrophysics, the mudrock line, (also called Castagna’s equation or Castagna’s relation), is an empirical linear relation between seismic P-wave velocity and S-wave velocity in brine-saturated siliciclastic rocks (i.e. sandstones and shales).Gardners Rule – relates seismic P-wave velocity to the bulk density of the lithology in which the wave travels. It can provide information about the lithology from interval velocities obtained from seismic data. The constants are usually calibrated from sonic and density well log information but in the absence of these, Gardner’s constants are a good approximation.