DEPTH PLOT BASICS
Log data depth plots are described by the depth scale, number of presentation tracks, and the curve names and scales for each that appear in each track. Logs recorded in the field usually have 3 tracks, one on the left of the depth values and two on the right, the latter may be combined into a single wide track. Depth plots that contain computed results, with or without raw data, can have any number of tracks.

The tables below give details of the common depth scales and curve complement for a few of the more common log suites. The curve name table shows the so-called "correlation track" first; it would appear as the left hand track of almost every depth plot.

A composite plot can merge several log displays into a single plot with any number of tracks, and may also have tracks with computed petrophysical results.

Customized depth plots are common, but to make life easier for those who have to use the data, it pays to make the plots as uniform as possible. This means the curve scale direction,  scale values, line colours, line codes, and overall layout are consistent over time and location.

An excellent low-cost LAS File View and Depth Plot program is available at Everett Energy Software. Follow the link to view a detailed features list.

PRACTICAL CONSIDERATIONS
Traditional depth plots of well log data are 8.25 inches wide so they can be printed on standard 8.5 inch paper at full size. If you create a wider plot, printer defaults will shrink both width and length so it will no longer be at the depth scale you specified. You can still see it full size on the computer screen but not on a simple printer. Professional software and wide bed printers overcome this limitation.

For the well log descriptions listed in the tables below, the standard API well log layout is recommended. It consists of 3 tracks, each 2.5 inches wide, with a 0.75 inch wide depth track between Tracks 1 and 2. See examples in the next Section. Each track is divided vertically into 10 equal divisions for linear scales, or into 3 or 4 logarithmic cycles for logarithmic scales.

A log header with log name and well location (and other useful information) is placed at the top of the log, followed by the curve names and scale information, centered over the appropriate track. Most log headers generated by commercial software omits critical information. The header should include the analyst's name, contact information, and time/date stamp. There is nothing more frustrating than trying to sort these items out two years after the plot was made.

For composite plots of raw data or computed results, a 4 track presentation that fit standard printers is a de facto standard. It consists of a 0.5 inch depth track on the left, followed by 4 tracks of width 1.875 inches. More width and more tracks are often seen, but usually at reduced scale when printed, except for those with expensive wide bed printer/plotters.

An excellent low-cost LAS File View and Depth Plot program is available at Everett Energy Software. Follow the link to view a detailed features list.

LAS file editing and repair software is available from KC Petrophysics (free and commercial versions). Follow the link to view a detailed features list.


DEFAULT  PLOT  LAYOUTS
 

DEFAULT  PLOT  LAYOUT  EXAMPLES

Typical resistivity log (left) and sonic log (right) displayed on traditional log tracks. Correlation curves in Track 1 to the left of the depth track and specific log curves in Tracks 2 +3.  Shading on sonic log indicates bad data caused by fractures.


Density neutron PE log on Limestone scale (left) and same log displayed on Dolomite scale (right). Red shading indicates density neutron crossover which could indicate light hydrocarbons OR limestone. PE curve indicates pure dolomite so crossover shows gas or very light oil.


Composite plot in this example combines correlation and resistivity tracks, with porosity,
 saturation, permeability, and lithology results tracks.