Page 388 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 364

[ ] Practical Wellsite Operations
3.3.3

should drop when pumping ceases to the level supported by the for-
mation fluid pressure, and the cement that has moved up the annulus
will probably drop down back to the loss zone.

3.3.3. Washout Detection Procedure

A washout occurs when a hole appears in the drillstring. This
may come from erosion, a damaged tool joint face, or a crack in the
string. If left uncontrolled a washout can quickly become a drillstring
failure because most drilling fluids are fairly abrasive and will soon
cut metal away under high pressure. An otherwise avoidable fishing
job will result.
Washouts can be prevented by regular inspection of the drillstring
components, ensuring correct handling and torquing up of the drill-
string and avoiding excess fatigue stresses (see Section 1.5.2, “Dogleg
Severity Limits—Combined Buildup and Turn”).
A washout may be suspected when a steady drop in circulating
pressure is seen with steady pump rates, no change in mud properties,
and no other apparent symptoms. This can usually be seen by looking
at the geolograph chart recorder. Determining that a washout has
occurred is a process of elimination.

1. Eliminate a formation fluid influx. Reducing surface pressure
could be caused by a kick. Flowcheck before doing anything else.
If that is OK, then:
2. Eliminate a leak in the high-pressure rig system or a change in
mud properties. Close the lower kelly cock and pressure test the
system from the pumps to the kelly cock. With pressure on, com-
pare the gauge readings on the driller’s console, standpipe mani-
fold, and choke panel to ensure that a gauge problem has not
caused the alarm. While that is happening, check that no fresh
mud, water, or chemicals were added to the system giving a change
in mud rheology. If that is OK, then:
3. Eliminate a drop in pump efficiency. Take pressures with each
pump at the same slow circulating rate that was last taken (usual-
ly at the beginning of the tour or when the bit got to the bottom).
If one pump shows lower pressure than before, check out the fluid

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