Page 193 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 169

2.3.2
Directional Planning [ ]

(saline water based). An alternative to this is using a side entry sub,
leaving the downhole probe permanently on-line. The main problem is
if the BOPs have to be closed because the wire will be outside the drill-
string and the BOP may not seal around it. The wire is also quite like-
ly to be damaged if the BOP is closed.
Directional surveys from wireline logging tools. Logging tools
that are run at the end of a hole section can give directional surveys.
If one of these tools is to be run anyway, it may be possible to save
the time/cost of running a multishot survey. A wireline logging tool
will also give very short intervals between stations (the survey is con-
tinuous), which should allow for a more accurate determination of
wellbore position.
Dipmeter tools require an accurate wellbore location to give actu-
al magnitude and direction of dip from the measurements that the tool
takes while logging. A directional plot can therefore be obtained from
a dipmeter run. This survey will have to be “tied back” or attached to
a previous survey that gives a known wellbore location, inclination,
and azimuth at or closely above the top of the surveyed interval.
Schlumberger FMS and FMI logs also give directional surveys.
Before relying on these tools to avoid running a separate gyro mul-
tishot, check to ensure that the logging tool surveys can be used as
definitive surveys per local government regulations and your own
company policy.
Schlumberger also has a north-seeking gyro survey tool. It locates
its own position on the Earth but unfortunately has to be left station-
ary for a long time in the rotary table to do this. Calibrating the tool
prior to the run can take a very long time and probably for this reason
does not seem to be run that often.
Monel drill collars and stabilizers—selection and use. The steel
contained in the drill string components can become so strongly mag-
netized that it creates large errors in magnetic compasses. Monel drill-
string components are not magnetic and are run to give a sufficient dis-
tance between the surveying instrument and the magnetic fields of the
steel drill collars. The distance necessary to give sufficiently low errors
can be calculated; it varies by the inclination and azimuth of the well-
bore at the point of measurement. Refer to Figure 2-6.

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