Page 369 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 345

Drilling Fluid [ ]
3.2.2

The size of the centrifuge is expressed as the bowl diameter and
length, for instance 18 in x 28 in. A larger centrifuge can process more
mud to the same size of separation, or the same amount of mud to a
finer separation, than a smaller centrifuge.
All the other equipment described above processes the full mud
flow rate; the centrifuge only processes part of the mud stream. When
drilling is slow and relatively frequent trips are made (during which
centrifuging continues), then one centrifuge is usually sufficient to
keep up with the small solids entering the mud. It may be necessary to
use some mud dilution when drilling fast with few trips in order to
maintain the programmed properties, unless a second centrifuge can be
obtained or the deterioration in properties tolerated.
Adjustment and maintenance of the centrifuge is best left to a tech-
nician who is familiar with the particular model of centrifuge. You can
choose to have the feed rate adjusted to process relatively high volumes
to a coarser particle size, or reduce the feed rate to remove finer parti-
cles—down to 2 micron (barite size) should be possible in water-based
mud. These adjustments are not obtained simply by changing the rate
of mud supply to the centrifuge, but changes are made in the centrifuge
to the overflow port settings as well.

3.2.2. Quality Control

Are you getting what you pay for? If not you may get things you
did not bargain for, which can cost you a lot both in mud treatment
costs and in unnecessary drilling problems. Section 2.5.13, “ Tendering
for Mud Services,” contains some information to incorporate at the
tender stage to ensure the correct quality chemicals are supplied.
Many problems are caused by contaminated chemicals. This may
occur accidentally with bulks (e.g., using a hose previously used for
bulking cement, when loading barite, has happened!) or may occur
deliberately when the mud contractor has supplied chemicals “cut”
with something cheap and bulky, to increase profit at your expense.
Logistical tricks of the trade include sending out drums that are
not full and loading pallets so there is an empty space in the center
where it cannot be seen until the pallet is used. The pallet trick is a
good one especially where the whole pallet is covered in a plastic sheet
for weather protection; it cannot be checked when first received and

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