Page 376 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 352

[ ] Practical Wellsite Operations
3.3.1

weight may help to stop the caving, depending on the cause of the cav-
ing, (if this will not cause losses), and cavings may cause a dirty annu-
lus during the trip, giving problems even if the hole was clean at the
start of the trip.
If the well cannot be cleaned by normal circulation for holes up to
45° inclination, circulate around a high viscous pill while moving the
string to disturb the cuttings beds. In higher inclinations, turbulent
flow is more effective, therefore, a low vis pill at high rate while mov-
ing the string may work better. In very high-angle holes using OBM,
pumping a base oil pill for turbulence can strip off the wall cake and
cause the hole to collapse as the hydrostatic will not then fully support
the bore wall.
On tripping out, steadily increasing drags will indicate dirty hole.
This could be caused by not circulating clean, or possibly by higher
formations caving into the hole even after circulating clean. In a devi-
ated well, cuttings beds may accumulate on the low side, which can be
hard to shift; this problem gets worse with increasing hole angle and
washouts.
The immediate actions are to stop pulling out and to clean up the
wellbore. If circulating normally has not cured the problem, consider
additional measures. This could include pumping at higher rates, rotat-
ing and reciprocating the pipe to disturb cuttings beds, pumping high,
or low viscosity pills as noted above.
Getting stuck by packing off on cuttings beds is a difficult situa-
tion. Circulation will probably not be possible and the string may not
move at all. The sticking force will increase with time as more solids
settle around the string. Keep pressure on the standpipe (not so much
as to induce losses) and try to work the string down, using torque if
possible. Once circulation is re-established, circulate as fast as possible
and continue to work the string down. Once free, clean up the well
before continuing with other operations.
It is possible that the string cannot be freed by these methods. The
alternatives are then to backoff and either wash over the string, side-
track, or abandon the well.
If a decision is made to wash over the string, it is best to washover
and recover in one run without stopping circulation. Otherwise, while
the washover string is being pulled and the fishing string run, solids
may again settle around the fish. Backoff at a convenient depth just

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