Short Normal Log is the type of Electrical Survey which was invented by the Schlumberger Brothers in 1927. And later it was replaced by Induction log and Laterolog in 1950s and 1960s.

1. WELL LOGGING

2. Short Normal Log (SN Log)
TOPIC

3. • Short Normal Log is the type
of Electrical Survey which
was invented by the
Schlumberger Brothers in
1927. And later it was
replaced by Induction log and
Laterolog in 1950s and 1960s.
HISTORY

4. • It measures resistivity with
direct current (DC) or low
frequency alternating current
(AC) using the principles
of Ohm’s Law.
PRINCIPLE

5. • The basic measuring system
has two current electrodes, A
and B.
• Two voltage measuring
electrodes, M and N.
TOOLS
A COMBINED LONG
AND
SHORT NORMAL MEASUREMENT

6. • A current is passed between A
and B, and the resulting voltage
is measured at M and N.
WORKING

7. FORMULA FOR FORMATION RESISTIVITY
CALCULATION
• If the formation is uniform, the formation resistivity, Rt, can be
computed from the formula:
Rt = K * V / I
• Where V is the voltage between M and N,
• I the intensity of the current flowing from A to B.
• K is a geometric factor that depends upon the relative distance
between A, B, M, and N and is a constant for a given electrode
arrangement.

8. UNIT
• Ohm-metre

9. LOG SPACING FOR SHORT NORMAL LOGS
• Log spacing is the distance AM, usually 16 inches for the short
normal.
• There is a second M electrode at a 64 inch spacing for the long
normal.
• The N electrode in the actual circuit is placed about 18 feet above
the tool to reduce resistance effects from the near surface due to dry
or frozen ground.
• The electrode spacing is measured from the center of the “A”
electrode at the bottom of the tool to the center of the “M” electrode.

10. ADVANTAGE OF SHORT SPACING IN
SHORT NORMAL LOG
• The advantage of 16 or 8 inch spacing is that thin beds are better
defined.
• When invasion is important, It is necessary to measure at least two or
more horizontal depths. Using two or more electrode spacings it is
possible to define zones that have invasion.
• Two resistivity curves can show relative “ability of formations to
produce”.
• Invasion curves are available for determination of invasion related to
differences in deep and shallow resistivity.

11. DRAWBACK
• It did not work in cased holes.
• Thickness of the bed is more.
• Not correct reading for beds whose thickness equal to 3 feet or 36
inches or more.
• If the bed thickness is less then 6 Inches it also show disturbance in
readings.
• It worked poorly in salty mud.

12. Composite of gamma, short-normal resistivity, fluid column
resistivity, caliper, and televiewer logs.