Pre-stack Inversion: Log Analyses
The Log Analysis tab shows a display of various elastic logs commonly used in the industry, derived from the three fundamental logs – Vp, Vs and Density (Rho). Other, petrophysical logs may also be sensitive or important to evaluating the data such as gamma ray, water saturation, total organic carbon (TOC) so they can also be displayed alongside (taken straight from Kingdom).
From the series of displays you can pick up on what elastic properties can be used and the sensitivity of the logs to the prospect with some elastic logs being sensitive to fluid while others are sensitive to lithology or rock matrix.
Any number of logs can be displayed dependent on how many you have selected.
The logs plotted are useful for typical sand classification.
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.
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
Polygons can be drawn over areas of the cross plot where shales, for example are thought to be. The data point samples within the polygon will be highlighted on the well log in the Log Analysis tab thus showing you can isolate lithologies by elastic parameters.