Page 108 - Basic Well Log Analysis for Geologist

GAMMA RAY LOGS

Figure 37. Example density log with gamma ray log. This example illustrates the curves and scales of a gamma ray log, and is
also used to pick values for Figure 38.
Track #1—The gamma ray log is the only one represented on this track. Note that the scale increases from left-to-right,
and ranges from 0 to 150 API gamma ray units.
‘Tracks #2 and #3—These tracks include logs representing bulk density (p,). density porosity (¢,)). density correction
curve (A,,), and a tension curve,
Bulk density (p,) is represented by a solid line and ranges from 2.0 to 3.0 gm/ce increasing from /efi-to-right.
Density porosity (@p) is represented by a dashed line and ranges from — 10% to +30 increasing from
right-to-left. The correction curve (A,) is represented by a dotted-and-dashed line and ranges from —0.25 to
of
+(0).25 gm/ce increasing from left-to-right, but only uses the right half the track. The tension curve is a log that
measures how much weight is being pulled on the wireline during logging. It is represented by a broken line and
ranges from 2,000 to 12.000 Ibs increasing from right-to-left, but it only uses the right half of the track.
At the example depth of Figure 38 (13.570 ft). pick the gamma ray reading of the formation. It is 28 gamma ray units (the
scale measures in increments of 15 units: slightly less than two units from Q).
Next pick the minimum gamma ray reading from the log (13.590 ft: GR,in = 15 gamma ray units), and the maximum
gamma ray reading from the log (13,720 ft; GRyy, = 128 gamma ray units).

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