Page 137 - Shale Shakers Drilling Fluid Systems
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CHAPTE R SI X
Shale Shaker Screens
Shale shakers remove solids by processing solid- only screen cloths commonly used in the drilling
laden drilling fluid over the surface of a vibrating industry. The twilled square weave is used for
screen. Particles smaller than the screen openings coarser screens in the mining industry (Figure 6-
pass through the screen along with the liquid 1B). The plain dutch weave, mostly used as a fil-
phase of the drilling fluid. Larger particles and ter cloth, has small, triangularly shaped screen
trapped finer particles are separated into the shaker openings that allow very little fluid to flow through
overflow for discard. (Figure 6-1C).
The original criterion for early shale shaker The plain square (Figure 6-1 A) and rectangular
screens was a long screen life. This demand for weaves (Figure 6-ID) are simple over/under weaves
screen life was consistent with shaker designs and in both directions. These weaves can be made
solids removal philosophies of that period. Early from the same diameter wire in one or both di-
shale shakers could only remove large solids from rections. The square weave is made by making
the drilling fluid. The sand trap, reserve and set- the spacing between the wires the same in both
tling pits, and downstream hydrocyclones (if used) directions. The rectangular or oblong weave is
removed the bulk of the drilled solids. Today's made by spacing the wire in one direction longer
shale shakers are capable of using finer mesh than the wire in the opposite direction. The advan-
screens that remove more solids. tage of plain square and rectangular weaves is
For any particular shale shaker, the size and that they provide a flow path that has low resis-
shape of the screen openings have a significant tance to flow.
effect on solids removal. For this reason, the per- A specialty weave screen is available (Figure 6-
formance of any shaker is largely controlled by the 1E) that consists of coarse wires in the long di-
screen cloth used. Desirable characteristics for rection and multiple groups of fine wires in the
shaker screens are: narrow direction. The long, narrow openings pro-
vide low flow resistance and remove spherical and
1. Economical drilled solids removal chunky solids.
2. Large liquid flow rate capacity Layered screens were introduced to the indus-
3. Plugging and blinding resistance try in the late 1970s. They are often chosen be-
4. Acceptable service life cause they provide a high liquid throughput and
5. Easy identification a resistance to blinding from drilled solids lodg-
ing in the openings. A layered screen is the result
The first four items in the above list are largely of two or more wire cloths overlaying each other
controlled by the actual screen cloth used and the (Figure 6-2). Both square and rectangular cloths
screen panel technology. Improvement in shale can be layered, and reducing the diameter of the
shaker performance are a direct result of improved wires increases liquid throughput. A large assort-
screen cloth and panel fabrication. ment of opening sizes and shapes are produced
by the multiple screen layers and the diameter of
the screen wire. Because of this, a wide variety of
COMMON SCREEN CLOTH WEAVES particle sizes pass through the screen.
In 1993, a three-dimensional surface screen was
Some of the common cloth weaves available to introduced. The screen surface is corrugated, sup-
the petroleum industry are shown in Figure 6-1. ported by a rigid frame for use primarily on lin-
The plain square weave, plain rectangular weave, ear motion shale shakers. As drilling fluid flows
and the modified rectangular weave are the down these screens, solids are transported in the
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