TM 5-3820-256-10
(2)
When making the log, the bottom of the well casing will be detected when the probe enters it. The effect on
the curves will be that both fall off to extremely low values, 5 to 20 ohm-feet, and then remain fairly
constant. Where the casing is seated into very low resistive shale, it may be rather difficult to determine the
exact position of the casing by this method.
i.
The SP Curve.
(1)
The spontaneous potentials measured in a well are of great value in deep oil wells where saline waters are
encountered. For these situations, the SP curve exhibits a great deal of character and can be related to
relative changes in formation permeability.
(2)
When logging in fresh water horizons, the SP curve usually has too few features to provide any useful
information.
2-35.
Setting Surface Casing. (See figure 2-44). Surface casing is used when the overburden near the surface is
prone to "caving in". The following procedures are performed after only a shallow portion of the hole has been drilled.
a. Lubricate the o-ring in the coupling and assemble the coupling to the leader pipe assembly. Install the nylon
locking spline.
b. Install the elevators around leader pipe just below the coupling.
Figure 2-44. Setting Surface Casing
2-106
