Page 450 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 426

[ ] Practical Wellsite Operations
3.7.5

noted on the drilling program and is also marked on maps of the area
(which should be recent since variation changes over time).

3.7.5. Magnetic Single Shot Survey Tool

Refer to “Monel drill collars and stabilizers—selection and use” in
Section 2.3.2 for information on calculating the number of non-mag-
netic drill collars needed for taking magnetic surveys.
Alternative camera units. There are three different camera units
that use either a timer set at surface, a motion sensor, or a Monel detec-
tor that fires one minute after it detects the presence of a Monel drill
collar. If the survey will be run on wireline, the motion sensor or Monel
detector is preferable if the hole is not sticky, since it will fire 1 minute
after reaching bottom. If the survey barrel is to be dropped, either to be
fished on wireline or left in the string during a trip out, then use the
timer unit allowing at least two minutes per thousand meters plus a
minute for surface preparation prior to dropping (for example, at 4000
m allow 9 minutes). By using the correct unit, you will know exactly
when the unit will start to expose the film, without wasting time wait-
ing for the timer to go off long after reaching bottom. This allows the
string to be worked until a few seconds before the camera will go off—
an advantage if sticking is a problem.
Preparing the tool to take a survey. If the kit has not been run
recently, test whichever unit is to be used. Either set the timer, start it
going and time the bulbs lighting, or stand the unit in a corner with the
Monel test ring in place or with the motion sensor unit switched on.
All three bulbs should light for approximately 60 seconds when the
camera unit fires. If not, check the bulbs and batteries.
Once the camera unit to be used has been tested OK, screw onto
the bottom the angle unit relevant to the expected inclination. For low-
angle/vertical wells use the 0-10 unit, for higher angles use the one
with the maximum reading that is next above the expected angle. Look
at the camera loading gate and ensure that it is closed. Pick up the film
magazine; hold it in position against the camera loading gate. Pull the
loading lever right out and gently push it back in. If there is film in the
magazine, it should pick one up and push it against the closed gate.

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