Page 368 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 344

[ ] Practical Wellsite Operations
3.2.1

may be caused by overloading the cyclone. The cyclone is removing
more solids than can exit at the underflow discharge. The cure is to
reduce the solids content of the mud (by using other mud cleaning
equipment upstream or changing to finer shaker screens if possible), or
reduce the feed volume. If the desilters are showing rope discharge and
the desanders are not in use, starting up the desanders will be beneficial
and may solve the problem. The desanders allow the desilters to work
more efficiently and should normally be used, if available.
If the cone lining is worn it will affect the operation of the cyclone
and also could lead to rope discharge. Ongoing wear will be rapid and
eventually the lining will wear through if it is not changed.
Sometimes solid particles accumulate around the bottom of the
cone inside and affect the action of the cone to produce rope discharge.
Remove and replace the outlet pipe, flush with water inside the cone,
pipe, and manifold inlet.
If the feed inlet becomes partially or completely blocked, there will
be no spiral action and mud will simply fall out of the bottom. This
may be mistaken for rope discharge, but the mud will not have any spi-
ral motion. This wasted mud will contain mud that has already been
cleaned by the other cyclones in the bank (since mud will be flowing
back through the overflow discharge pipe from the discharge mani-
fold). Therefore, not only is mud being wasted, but the work of the
remaining cyclones is being compromised. The blockage must be fixed
or the cyclone removed from service and the inlet and outlet capped as
soon as possible.
Between wells it is worthwhile to remove the end cap from the feed
pipe and clear out the inside. It is amazing how often you come across
wood, rope, bits of cement plug, etc. in these feed pipes. This debris
can move and block the feed pipe.
If the underflow discharge should become blocked (or deliberate-
ly plugged with a bolt by someone who cannot be bothered to fix a
cone with excessive discharge), then the result will be high wear on the
cone lining and no discharge of solids. Uncleaned mud will be dis-
charged at the top to mix with the mud cleaned by the other cyclones
in the bank. The problem must be fixed, not hidden.
Decanting centrifuges. While there have been several types of cen-
trifuges used in mud solids removal applications, the only one likely to
be used on the rig is the decanting centrifuge. A detailed description of
the workings is not necessary here.

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