Page 375 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 351

Drilling Problems [ ]
3.3.1

When reaming a kickoff in softer formations, take precautions to
ensure that a sidetrack is not inadvertently drilled. Use low WOB/high-
er RPM and, if necessary, make a special trip with a bit-sized hole open-
er and a bullnose to ream out the hole before drilling ahead.
If stuck in this situation, jar and work the string upwards. The jar
should be free.
Ledges. Ledges may form where soft and hard formations alter-
nate. Run slowly when tripping in at these points. Note and ream any
resistance seen on trips.
To free the string if stuck by a ledge, jar up if stuck while running
in or down if stuck while pulling out.
Mobile formations. Sticking in salt may occur fast enough for the
bit to get stuck as it drills. This condition, if it occurs, is hard to avoid
altogether but may be reduced by using a water-based mud that leach-
es the salt slightly as drilling progresses. Higher mud weights may (or
may not) help to keep the salt under control. Bits are available that drill
slightly off center and therefore cut an overgauge hole; they may be
helpful when drilling in problem-flowing salts. If the string is sticking
while drilling or has high drags on connections, try drilling one or two
meters at a time, then pick up and ream down before continuing.
If the salt moves more slowly and causes problems mainly when
tripping back through it, try programming wiper trips through a newly
drilled hole after a short time (refer to “Undergauge hole” in Section
3.3.1, “Stuck Pipe”).
When stuck in salt, start jarring immediately and if not free with-
in a few jar blows, prepare a freshwater pill while continuing to jar. If
it does not jar free quickly, it is unlikely that jarring alone will free the
string. Analysis of cases of salt sticking indicate that once stuck in salt,
jarring alone only frees the pipe within the first 10 minutes.
If the well is likely to have other mobile formations present, wiper
trip and ream as dictated by hole conditions. If stuck, start jarring in
the opposite direction right away.
Cuttings beds. Ensure mud rheology and annular velocities are
sufficient to keep the hole clean while drilling. This will be more diffi-
cult as inclination increases. The most difficult hole to clean is between
45° and 55° inclination. Circulate clean at the highest practical no-loss
rate before pulling out, not just bottoms up, displacing a pill around if
necessary. If cavings are causing a problem, a slight increase in mud

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