Page 377 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 353

3.3.1
Drilling Problems [ ]

above the stuck point and then run the following fishing assembly:
Washover shoe and pipe, long enough to reach below the bottom
stabilizer or just above the bit sub to stab into the top fish connection
- circulating sub with the sleeve already open - drill collars - fishing jar
- drill collars - accelerator – HWDP, etc.
Washover the fish, screw into the fish without interrupting circu-
lation, continue to circulate, and pull/jar free. By having the open cir-
culating sub inside the top of the washover pipe, circulation is main-
tained all the time, even if the fish is plugged inside with solids (as is
likely).
Reactive formation. There are two types of reactive formation:
those that hydrate and slough in (Gumbo) and those that collapse due
to brittle failure. Both types are likely to be time sensitive, therefore,
the casing program should allow them to be cased off within the time
that they stay stable.
In the first case, ensure that the level of inhibition is carefully
maintained as per program and increase if necessary. Monitor the con-
dition of the cuttings for signs of hydration. Minimize swab and surge
pressures. Plan operations to minimize the time spent with open hole
before running casing, but do not take risky short cuts.
For brittle failure type formations, higher mud weight is the best
stabilizing mechanism. Ensure that the hole is kept clean while
drilling. Avoid drilling at critical rotary speeds to minimize string
vibrations. Minimize swab and surge pressures.
For both types of reactive formation, consider wiper trips careful-
ly. Wiper trips should only be done when the wiper trip is likely to help
improve the overall situation. Refer to Section 3.3.8, “Preplanned Wire
tripping,” for general information on wiper trips. Trip carefully and
start up and stop the pumps slowly to minimize swabs and surges, all
of which can help destabilize the formation.
In the case of pipe sticking due to reactive formation collapse or
sloughing, refer to the method discussed in the Section 3.3.1, “Cuttings
beds.” Also see the wellbore stability topics in Section 2.9.1.
Tophole collapse. This may occur since very shallow formations
are unconsolidated and there is little overbalance to help stabilize the
wall. If possible, drill with returns to the rig (for greater hydrostatic)
on an offshore well, and use a mud with good wall cake-forming char-
acteristics or pump high solids slugs around to help plaster the hole.

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