Page 367 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 343

3.2.1
Drilling Fluid [ ]

Balanced hydrocyclone adjustment. When the hydrocyclone is
adjusted with too small an underflow opening, the point at which the
mud changes direction will be too far above the opening and very fine
solids will then be deposited on the cone wall instead of being dis-
charged. The end result will be a plugged cone and no solids discharge.
The opposite can also occur, resulting in a discharge of a hollow spi-
raling cylindrical shape of mud and discharged solids. This second
condition gives fairly efficient solids removal and does not lead to high
mud losses unless it is excessive. As with spray discharge, suction can
be felt at the bottom, which may be used to differentiate the condition
with rope discharge.
The ideal adjustment of opening, feed rate, and feed pressure with
correct chamber design (and an unworn lining) will give a spray dis-
charge of damp solid particles and suction of air into the underflow
opening, which can be felt with a finger. This leads to the most effi-
cient, lowest cost operation with low cone wear. If this suction can be
felt then the cone is working well.
Use of hydrocyclones and mud cleaners with oil-based mud.
Desilters are not usually used with OBM because the discharge will
contain a relatively large percentage of oil. If a cone malfunctions then
large quantities of expensive mud can be lost. Environmentally this is
unacceptable as well as expensive.
If the discharge from the desilters can be routed over a vibrating
screen (such as a mud cleaner), then the desilters can play a valuable
part in removing undesirable solids.
Mud cleaners are simply banks of desilter size cones (4 in to 6 in)
over a fine mesh vibrating screen.

Hydrocyclone cone capacities

4 in 50 GPM/cone 12-60 micron cut size
6 in 100 GPM/cone 20-60 micron cut size
8 in 155 GPM/cone 30-60 micron cut size
10 in 500 GPM/cone 30-60 micron cut size
12 in 600 GPM/cone 30-60 micron cut size

Problems with hydrocyclones. Rope discharge from a hydrocy-
clone—a characteristic solid stream of spiraling mud with no suction—

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