Page 449 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 425

3.7.4
Directional Drilling [ ]

There is an exception to the rule of not jetting more than a short
distance on each kelly. Large hole (over 16 in) is difficult to jet, but is
possible. Jetting may have to be done for a full kelly down followed by
a rotary drilled kelly down.
Smith Tool produces a special bit for jetting. This is like a tricone
bit with one cone missing and a large circulation slot where the third
cone would normally be. This bit has a right-hand walk tendency.
Marine wholesale distributors tools are not used when jetting due
to the large flow rates necessary. Single shot surveys are quite adequate
(and much cheaper) than MWDs and string orientation is accurate
from the table because there will be little difference between bit and
kelly direction due to the shallow depth.
Since drilling is fairly fast and the annulus will get loaded up with
cuttings, a float in the string is necessary. Otherwise, time will have to
be spent on circulating before every survey to prevent strong backflow.

3.7.4. Single Shot Surveys—General Points

The hole should be clean before running the survey and with no
serious concerns as to hole condition. It is possible to take surveys in
fairly sticky hole with a lot of care, using a timer unit and stopping the
bit off bottom about 10 seconds before the survey, starting to move the
string down, initially, 60 seconds after stopping.
A kelly cock should always be put on the top of the string and if
wireline is to be run through it, use a metal protector with the bottom
cut out to prevent the line cutting the thread.
Sandline should not be used for running or pulling surveys if there
is an alternative. It is hard to control and the wire will twist up into a
tangled mess when the tension is released as the survey barrel lands,
unless the drum is stopped immediately. If it is used, do it with care
and keep everyone clear of the rotary. Rigs should be equipped with a
slick wireline winch.
The azimuth read from the magnetic compass should be corrected
for magnetic variation. If the variation is east, add the variation to the
magnetic azimuth. If the variation is west, subtract it from the mag-
netic azimuth to give the corrected azimuth. The variation should be

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