BAKER HUGHES - Drilling Fluids Reference Manual

MECHANICAL SOLIDS CONTROL
for high-gravity solids. Feed rates normally run from 10 to 40 gpm depending on the
density of the whole fluid. This centrifuge will strip barite above the cut point from the
fluid and discard the liquid phase with the remaining fine solids.
2. High Volume Centrifuge – Used primarily for discarding low-gravity solids from the
fluid. It is so named because processing rates range from 100 to 200 gpm. Normal rpm
ranges from 1900 to 2200 rpm. G-forces average about 800 Gs. The cut point attained is
from 5 to 7 microns on unweighted fluid applications.
3. High Speed Centrifuge – Used for removal of low-gravity solids from unweighted fluid
systems and as second centrifuge in dual-centrifuging applications. This group of
centrifuges turn from 2500 to 3300 rpm. G-forces created by these units range from
1200 to 2100 Gs. Cut point can be as low as 2 to 5 microns. Feed rates will range from
40 to 120 gpm depending on application and the fluid to be processed.
The term dual-centrifuging comes from the use of two centrifuges in tandem. Effluent from a barite
recovery unit is used to feed the second centrifuge. The benefit of this operation is that some solids
can be removed from the low end of the size range without the loss of the fluid phase.
For example, if the barite recovery unit is making a cut at 8 microns, then the fluid feed to the
second centrifuge will basically have solids 8 microns and smaller. The second centrifuge should
be capable of achieving higher Gs than the first and make a cut in the 2- to 5-micron range. The
fluid phase is returned to the fluid and the solids discarded from the system. As demonstrated, this
combination of centrifuges does not remove the ultra-fine and colloidal solids from the system, but
it does remove solids that may be degradating down to that range. This will prolong the need for
dilution and displacement of the fluid. Dual centrifuging has possible economic justification in
situations where environmental restrictions will not allow reserve pits, or where the liquid phase of
the fluid has high economic value. It needs to be remembered, though, that the use of these units
will not solve any solids problems with the fluid, only delay them.
The principle of the decanting centrifuge is illustrated in Figure 10-6
Figure 10 - 6 Solid Bowl Decanting Centrifuge
BAKER HUGHES DRILLING FLUIDS
REVISION 2006 10-16
REFERENCE MANUAL