(1) Depth scale. Depth scales vary with locale and requirements. Most single logs are recorded on two different films at once, and the two films may optionally be on different depth scales. One film may be for correlation and the other tor detailed interpretation, or one may be for normal use and the other for quick-look interpretation by the overlay technique.
In North America the depth scales for correlation use are: 1 or 2 in. of film per 100 ft. of hole (i.e., on a scale of 1:1200 or 1:600 in terms of feet of film per feet of hole). The usual scale for detail use is: 5 in. of film per 100 ft. of hole (i.e., 1:240). An expanded scale of 25 in. per l00 ft. (l:48) is available for close scrutiny of short sections, and a special 60 in. per 100 ft. scale (1:20) is used for dipmeter logs.
Most of the rest of the world uses decimal scaling (1:1000, 1:500, 1:200, 1:40, 1:20) based either on the foot or the meter. Metric logs are easily identified by the fact that depth numbers appear at each 50-m. level, while logs scaled in feet have depth numbers at each 100-ft. level.
(2) Grid scale type. Usualy linear, logarithmic, or split. Observe illustration. The hybrid scale, which is not shown, was used before the logarithmic scale for use with laterolog type surveys.
(3) Grid scale sensitivity. The scale on which the magnitude of the measured signal is recorded. It corresponds to the value given to the full-scale deflection of the galvanometer or pen, or the width of one track (100 small divisions) on linear scales; center or midscale (one-half width of one track = 50 small divisions) on hybrid scales.
(4) Chemical scale. A deposit that accumulates on solid surfaces (e.g., casing. tubing, rock. etc.) or in perforations and other apertures. It reduces fluid production from the formation.