Page 129 - Shale Shakers Drilling Fluid Systems

112 SHALE SHAKERS AND DRILLING FLUID SYSTEMS
of a linear motion shaker. Line size and potential
head losses must be considered with this arrange-
ment to avoid overflow and loss of drilling fluid.
This design may reduce overall cost by using ex-
isting equipment. This concept, where space is
available, has the advantages of highly visible
screening surfaces and ease of access for repairs.
The disadvantage of separate individual shakers is
the space needed for mounting the shakers and
the extra piping needed to tie the scalping shak-
ers to the flow-line shakers.
The integral Unit with Multiple
Vibratory Motions
This design type combines the two units of the
separate unit system into a single, integral unit
mounted on a single skid. Usually, a circular mo-
tion shaker is mounted above a linear motion
shaker on a common skid (Figure 4-3). The under-
flow (liquid mud) from the top scalping shaker is
directed through a flowback, sheetmetal pan onto
the back of the bottom flow-line shaker. The pri-
mary advantages of this design are reduced instal-
lation costs and space requirements. The internal
backflow pan eliminates the manifold and piping
needed for the two separate units. By mounting
the units above one another, normally the flow
line entry height and the weir height of the mud
flow on the scalping shaker, is lower than that of
separate units.
FIGURE 4-3
The disadvantage of this design is the limited
visibility of the upper and lower screens, due
to the height of the scalper shaker and the min-
imum clearance between the upper and lower
shakers. On some models, it is also difficult to
perform routine maintenance and replace vibratory
drive components.
The integral Unit with a Single
Vibratory Motion
This design consists of an integral unit with a
single vibratory motion, as shown in Figure 4-4.
Typically, the units use linear motion shakers and
incorporate a scalping screen in the upper part of
the basket. The lower bed consists of a fine screen
mesh, flow-line shaker unit and the upper scalper
section is designed with a smaller-width bed, us-
ing coarse mesh screens. Most of the available
single vibratory motion shakers use hook strip-
type screens for the upper scalping deck and the
lower section deck designs vary from hook strip
to pretension framed screens. Compared to the
cascade shaker units, this design significantly low-
ers the weir height of the mud inlet to the upper
screening area.
Conversely, as with the cascade shaker units,
the visibility and access to the fine screen deck
of the single vibratory unit is limited by the slope
of the upper scalping deck.
Summary
Cascading systems use one set of shakers to
scalp large solids and/or gumbo from the drilling
fluid and another set of shakers to remove fine
FIGURE 4-4