Page 169 - Shale Shakers Drilling Fluid Systems
P. 169
152 SHALE SHAKERS AND DRILLING FLUID SYSTEMS
When balanced cones no longer operate with Hydrocyclone installation Tips
spray discharge, either too many solids are
being presented for design processing, large • Hydrocyclones should be located so that under-
solids have plugged the manifold or apex, or flow can be removed with a minimum of
the feed pressure is incorrect. If the feed trouble and wash-down water. They should
pressure is correct at 75 feet of hydraulic be located so they are accessible for main-
head, often the inability to maintain spray tenance and evaluation.
discharge can be attributed to the shale shak-
ers. Check for torn screens, open bypass, or • Discharge overflow should return to the cir-
improperly mounted screens. Additionally, culating system into a compartment immedi-
ensure that there are sufficient hydrocyclones ately downstream of the suction compart-
to process the total fluid being circulated by ment. At the same time, the discharge overflow
the mud pumps. compartment must be bottom equalized with
the suction compartment and drilling fluid
Install a low ("bottom") equalizer to permit should backflow from the discharge tank into
backflow from the discharge tank into the suc- the suction tank at all times. The hydro-
tion compartment. Removable centrifugal pump cyclones should process all drilling fluid en-
suction screens reduce plugging problems.
tering its suction compartment. Ensure that
Operate hydrocyclones at the recommended all drilling fluid entering the discharge compart-
feed head of approximately 75 feet. Efficiency ment has been processed by the hydrocyclones.
is decreased by operating at too low a feed
head. Operating at too high a head wears • Centrifugal feed pumps should be located so
hydrocyclone parts and yields insignificant that they have flooded suction, minimum
separation improvements. suction line length, with few elbows and turns
to minimize friction losses.
Do NOT use the same pump to feed the desilter
and desander. Each unit should have its own • A centrifugal pump may stir its suction
centrifugal pump(s). compartment with mud guns. Mud jet mixers
Run the desilter continuously while drilling with should not be supplied with fluid from other
unweighted mud and process 100% of the to- parts of the drilling fluid system. Preferably,
tal surface pit volume after beginning a trip. mechanical agitators should be used in the
removal section.
Operate the desander when shale shakers will
not screen down to 140 mesh (100 microns). • Keep the end of the discharge line above the
Install a guard screen with approximately surface of the mud in the receiving tank to
half-inch openings to prevent large debris avoid creating a vacuum. Overflow should be
from entering and plugging the inlets and/or introduced into the next compartment down-
cone apexes. stream at approximately a 45° angle so lines
will be kept full and a siphoning vacuum,
Regularly check cones for bottom plugging or which would pull more solids into the over-
flooding. Desilter cones will plug more often flow discharge, avoided. When hydrocyclones
than desander cones. Plugged cones may be are mounted more than five feet above the
cleaned with a welding rod. A flooded cone liquid level of the mud tanks, a siphon breaker
indicates a partially plugged feed or a worn should be installed in the overflow manifold
cone bottom section.
from the cones.
Between wells, or when drilling is interrupted,
flush manifolds with water and examine the Conclusions
inside surfaces of the cones.
Keep the shale shaker well maintained and Hydrocyclones are simple, easily maintained
never bypass it. mechanical devices without moving parts. Sepa-
ration is accomplished by transfer of kinetic input,
Hydrocyclones discard absorbed liquid with or feed energy, into the centrifugal force inside the
the drilled solids. Discharge solids dryness is cone. The centrifugal force acts on the drilling
a function of the apex opening relative to the fluid slurry to rapidly separate drilled solids and
diameter of the vortex finder.
other solid particles in accordance with Stokes' Law.
Mud cleaners and/or centrifuges can be used The solids generated while drilling in some for-
to process the cones underflow. mations are too fine for shale shakers to remove.
