Page 249 - Shale Shakers Drilling Fluid Systems

EQUIPMENT GUIDELINES 231
Jet and venturi hoppers suck air into the mud
during mixing.
Hoppers should be turned off when they are
not being used. At the discharge end of the
additions line, an inexpensive air removal cyl-
inder can be added without creating much
backpressure. This involves a piece of 13-f-
inch to 20-inch casing approximately 1 y-feet
tall, vertically welded to the end of the
hopper discharge line. A plate with an 8- to
10-inch diameter hole is welded on the top of
the casing. Fluid enters tangentially and is
swirled as it encounters the piece of casing.
This swirling action causes drilling fluid to
move to the outside wall, and the air moves
to the inside. This acts as a centrifugal sepa-
rator (see Figure B-l). Air exits through the
hole at the top and the drilling fluid drops
freely into the pits.
36. Jet hoppers should include a venturi for better
mixing.
A venturi is needed if the flow line rises to an
elevated position. The device converts a ve-
locity head to a pressure head. Without it,
fluid does not have enough pressure to rise
over the tank wall.
FIGURE B-1
37. The Check/Suction Section of the surface sys-
tem should contain a 20-50 barrel slugging tank
which includes a mud gun system for stirring
and mixing.
An agitator may be used in addition to the
mud gun. The mud gun system can be con-
nected to the pump that is used to fill the slug
tank. Usually the slug tank is used to prepare
a drilling fluid with a higher density. This
"slug" is pumped into the drill string. When
tripping drill pipe, the fluid level inside the
drill pipe will remain below the surface. This
prevents spilling drilling fluid when a stand is
removed from the drill string. Failure to slug
the pipe, or get a good "slug," results in drill-
ing fluid splashing the rig crew as the pipe is
pulled and racked.
38. Mud premix systems should be used on any
mud system whose additives require time and
shear for proper mixing. Premix systems should
especially be used on systems requiring the ad-
dition of bentonite, or hard-to-mix polymers,
such as CMC, PHPA, XC, etc.
To be effective, bentonite must be prehydrated
and dispersed into platelets as small as pos-
sible. It should be added to a well-agitated
tank of fresh water. No other additives are
required. The addition of lignosulfonate will
inhibit dispersion as it thins the slurry. Ben-
tonite should be allowed to hydrate for 24
hours (8 hours minimum). Polymers, such as
HP007, require many hours of prehydration
and shear before use.
39. Special shear and mixing devices are recom-
mended for premix systems for mixing polymers
(especially PHPA), spotting fluids, specialized
coring fluids, and for hydra ting bentonite.
Centrifugal pumps are available that have a
modified impeller with holes or nozzles through
which the fluid shears. These systems are very
effective for shearing polymers.
40. High-shear devices should not be used on the
active system because they will rapidly reduce
mud solids to colloidal size.
Drilled solids are not processed in the same
manner as bentonite. The purpose of dispers-
ing bentonite is to take advantage of the very
thin clay platelets and their electric charges.
Drilled solids usually will not grind as thin as
bentonite can disperse. Although they become
colloidal, they are still 1,000 times larger than
bentonite platelets. Increasing the colloidal