Page 378 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 354

[ ] Practical Wellsite Operations
3.3.1

To get free, try to establish circulation while working the string
down and applying torque. If off bottom, a surface jar may help to get
movement and circulation. Once circulation is established, pump as
fast as possible without inducing losses and try to clean up the well.
Keep the string moving. On a floating rig, use the riser boost pump to
help lift the debris to surface.
Geopressured formation. In shales where the formation pore pres-
sure is greater than the mud hydrostatic, slivers of formation will tend
to be pushed into the wellbore. Use higher mud weight, if possible, to
reduce or eliminate this and keep the hole clean, using pills if necessary.
Where the formation is left exposed for a long time, very large
washouts can occur that may lead to other problems with large
chunks of formation falling in, big cuttings beds forming, fish becom-
ing impossible to recover (if they fall over in the washout,) and bad
cement jobs. If the formation cannot be controlled with mud weight,
then ensure that the casing can be run within a short time of drilling
the formation.
It may also be possible to displace cement into the washouts and
drill through it, leaving the cement to stabilize the formations. Adding
fibers to the cement may be prudent to reduce the possibility of cement
blocks. Also, fiberglass pipe can be run as if it were casing, placing
cement in the washout and allowing a “pilot hole” through the cement
for drilling out.
In the case of pipe sticking due to geopressured formation collapse,
the method of recovery is discussed in Section 3.3.1, “Cuttings beds.”
Fractured and faulted formations. Some formations are already
naturally fractured before being drilled into. This can again cause large
chunks of rock to enter the wellbore causing mechanical sticking.
Since the damage is already done, avoid making it worse by minimiz-
ing swab/surge pressures and drillstring vibrations, drilling at low
angle if possible, getting through it quickly, and casing it off.
Circulation may well be possible if mechanically stuck with large
pieces of formation above the BHA. Maintain circulation and
work/bump the pipe down until free. Start with light bumps because
shock waves from the string may cause further bits of formation to
come loose. When the string can be moved down, keep the string mov-
ing and circulate clean. It may be necessary to backream up to pass the
obstruction. Ream carefully when running back in.

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