Chapter 3.

Shale Shakers

The shale shaker can be regarded as the “first line of defense” in the solids
removal system. It has proven to be a simple and reliable method of removing
large amounts of coarse, drilled cuttings from the circulating system. The shale
shaker’s performance can be easily observed; all aspects of its operation are visi-
ble. Shale shakers provide the advantage of not degrading soft or friable cuttings.
When well-operated and maintained, shale shakers can produce a relatively dry
cuttings discharge.

In unweighted muds, the shale shaker’s main role is to reduce the solids loading
to the downstream hydrocyclones and centrifuges to improve their efficiency. In
muds containing solid weighting agents such as barite, the shale shaker is the pri-
mary solids removal device. It is usually relied upon to remove all drilled cuttings
coarser than the weighting material. Downstream equipment will often remove too
much valuable weighting material.

Enough shakers should be installed to process the entire circulating rate with the
goal of removing as many drilled cuttings as economically feasible. Given the
importance of the shale shaker, the most efficient shakers and screens should be
selected to achieve optimum economic performance of the solids control system.

Shaker performance is a function of:

• Vibration pattern
• Vibration dynamics
• Deck size and configuration
• Shaker screen characteristics
• Mud rheology (plastic viscosity)
• Solids loading rate (penetration rate, hole diameter)
The impact of each is discussed in detail in this chapter. Guidelines for shaker and
screen selection are also provided.

Principle of Operation

Simply stated, a shale shaker works by channeling mud and solids onto vibrating
screens. The mud and fine solids pass through the screens and return to the
active system. Solids coarser than the screen openings are conveyed off the
screen by the vibratory motion of the shaker. The shaker is the only solids

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removal device that makes a separation based on physical particle size.

Hydrocyclones and centrifuges separate solids based on differences in their rela-
tive mass.

The screens are vibrated by rotating eccentrically-weighted shafts attached to the

basket. The major components of a typical shale shaker are illustrated in
Figure 3.1.

Figure 3.1 Shale Shaker Components. These components are common to most shale shakers.

Vibration Patterns
Shale shakers are classified in part by the vibration pattern made by the shaker
basket location over a vibration cycle (e.g., “linear motion” shakers). The pattern
will depend on the placement and orientation of the vibrators. Four basic vibration
patterns are possible: circular, unbalanced elliptical, linear, and balanced elliptical
motion.

Circular Motion

As the name implies, the shaker basket moves in a uniform circular motion when
viewed from the side (Figure 3.2). This is a “balanced” vibration pattern because
all regions of the shaker basket move in phase with the identical pattern. In order
to achieve “balanced” circular motion, a vibrator must be located on each side of
the shaker basket at its center of gravity (CG) with the axis of rotation perpendicu-

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lar to the side of the basket. The Brandt Tandem is a common example of a circu-
lar motion shale shaker.

Solids Conveyance and Fluid Throughput

Circular motion shakers will not efficiently convey solids uphill. Therefore, most
shakers of this type are designed with horizontal configurations. Fluid throughput
is limited by the deck angle, but augmented slightly by the higher G’s normally
used (see Vibration Dynamics section). The “soft” acceleration pattern does not
tend to drive soft, sticky solids, such as gumbo, into the screens.

Recommended Applications

• gumbo, or soft, sticky solids conditions

• scalping shakers for coarse solids removal

Figure 3.2 Circular Motion. All areas of the basket rotate in a circular motion.

Unbalanced Elliptical Motion

The difference between circular motion and unbalanced elliptical motion is a mat-
ter of vibrator placement. To achieve unbalanced elliptical motion, the vibrators
are typically located above the shaker basket. Because the vibrator counter-
weights no longer rotate about the shaker’s center of gravity, torque is applied on
the shaker basket. This causes a rocking motion which generates different vibra-
tion patterns to occur along the length of the basket, hence the term “unbalanced.”
Refer to Appendix E, Equipment Specifications, for a list of shakers having unbal-
anced elliptical motion.

Figure 3.3 illustrates how the vibration pattern may change along the length of the
basket. At the feed end of the shaker, an elliptical vibration pattern is created; the
angle of vibration is pointed toward the discharge end. In this region, forward sol-
ids conveyance is good. However, at the discharge end of the shaker, angle of the
elliptical pattern is pointed back towards the feed end. This will cause the solids to
convey backwards unless the deck is pitched downhill at a sufficient angle to
overcome the uphill acceleration imparted on the solids by the shaker motion.

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Solids Conveyance and Fluid Throughput

The downhill deck orientation restricts the unbalanced elliptical motion shaker’s
ability to process fluid; mud losses can be a concern. However, the deck orienta-
tion is beneficial for removing sticky solids such as gumbo.

Recommended Applications

• gumbo, or soft, sticky solids conditions

• scalping shakers for coarse solids removal

Figure 3.3 Unbalanced Elliptical Motion. The vibration pattern changes along the length of the
basket.

Linear Motion

Linear motion is achieved by using two counter-rotating vibrators which, because

of their positioning and vibration dynamics, will naturally operate in phase. They
are located so that a line drawn from the shaker’s center of gravity bisects at 90° a
line drawn between the two axes of rotation (Figure 3.4).

Because the counterweights rotate in opposite directions, the net force on the
shaker basket is zero except along a line passing through the shaker’s center of
gravity. The resultant shaker motion is therefore “linear.” The angle of this line of
motion is usually at 45-50° relative to the shaker deck to achieve maximum solids
conveyance. Because acceleration is applied through the shaker CG, the basket
is dynamically balanced; the same pattern of motion will exist at all points along
the shaker.

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Solids Conveyance and Liquid Throughput

Linear motion shakers have become the shaker of choice for most applications
because of their superior solids conveyance and fluid-handling capacity. Solids
can be strongly conveyed uphill by linear motion. The uphill deck configuration
allows a pool of liquid to form at the shaker's feed end to provide additional head
and high fluid throughput capability. This allows the use of fine screens to improve
separation performance. The Derrick Flo-Line Cleaner is one example of a linear
motion shale shaker.

One drawback to linear motion shakers is their relatively poor performance in pro-
cessing gumbo. The short vibration stroke length when combined with long, bas-
ket lengths, uphill deck angles and strong acceleration forces tends to make the
soft gumbo “patties” adhere to the screen cloth. Some success has been reported
by using linear motion shakers with short deck lengths and horizontal or downhill
deck angles.

Recommended Applications

• All applications where fine screening is required.

Figure 3.4 Linear Motion. All areas move in a synchronous linear motion.

Balanced Elliptical Motion

Amoco's analytical shaker dynamics model has predicted that this is the optimum
vibration pattern for maximum solids conveyance. Unlike “unbalanced” elliptical
motion, all points on the shaker basket move in phase with the identical elliptical
pattern. The model predicts that a “thin” ellipse will provide solids conveyance

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superior even to linear motion. Because elliptical motion provides a “softer” accel-
eration pattern than linear motion, it is likely that screen life may also be improved.

A simple and commercially-viable method to achieve balanced elliptical motion

has recently been tested. The vibrators are located as shown in Figure 3.5. The
vertical orientation of the vibrators dictates the shape of the ellipse. The more the
vibrators are tilted out from the shaker basket, the more circular the vibration pat-
tern.

Figure 3.5 Balanced Elliptical Motion. This motion is the most efficient in conveying solids.

Full-scale experiments have verified analytical model predictions of improved sol-

ids conveyance with a thin ellipse. In Figure 3.6, the numbers in parentheses are
the ratios of major axis length to minor axis length of the vibration patterns. By
adjusting the shape of the ellipse, solids conveyance velocity can be adjusted
without changing deck angle or acceleration normal to the screen. This feature
has potential for optimizing cuttings conveyance with respect to oil retention on
cuttings.

Vibration Dynamics

Acceleration

During the vibration cycle, the shaker basket undergoes acceleration which
changes in both magnitude and direction. As discussed previously, the placement
of the vibrators determines the vibration pattern and therefore the net acceleration
direction during the vibration cycle. The mass of the counterweights and the fre-
quency of the vibration determine the magnitude of the acceleration.

The vertical component of acceleration has the most effect on shaker liquid
throughput. We relate the vertical components of acceleration and stroke length to
frequency by the following equation:

2
stroke ( in.) × RPM
G‘s = --------------------------------------------------
70, 400

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Acceleration (normal to screen), G’s

Figure 3.6 Conveyance Velocity. The shape of the ellipse controls conveyance velocity. A thin
ellipse conveys solids faster than linear motion.

where the stroke length is the total vertical distance travelled by the shaker basket
and the G-force is measured from midpoint to peak.

An acceleration of one “G” is the standard acceleration due to gravity

(386 in./sec2). Most shakers operate at accelerations within the range of
2.5-5.0 G’s, depending upon the vibration pattern. Field experience has shown
this range offers the best compromise between throughput capacity and screen
life.

Many manufacturers report the acceleration of linear motion shakers along the
line of motion. This yields a larger number and looks good on the specification
sheet. However, unless the angle of vibration is also specified, it reveals little
about the performance of the shaker. The “G's” for shale shakers listed in the
appendix are calculated for the direction normal to the screen surface.

Some shakers have adjustable counterweights to vary acceleration (Figure 3.7).

Although flow capacity and cuttings dryness improves with increased accelera-
tion, screen life is negatively affected. By reducing the “G’s” when extra flow
capacity is available, screen life may be improved.

Frequency (RPM), Stroke Length

The vibrator frequency of most shale shakers is not normally adjustable. The
vibrators typically rotate at a nominal rpm of 1200 or 1800 at 60 Hz. Stroke length

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Figure 3.7 Adjustable Vibrator Counterweights. Other designs are used, this is the most
simple.

varies inversely with rpm. A higher rpm will result in a shorter stroke length at the
same acceleration.

The effect of vibrator frequency and stroke length on shaker processing rate has
been evaluated in the laboratory. The results of these tests show improved shaker
flow capacity in the presence of solids with decreased rpm (or conversely,
increased stroke length) at the same G level. (Figure 3.8). Therefore, the term
“high speed” should not be used to mean “high performance” since the opposite
relationship is often more correct.

The main disadvantage to lower frequency shale shakers is that the mud tends to
“bounce” much higher off the screens and cover the area around the shakers with
a fine coating of mud. More frequent housekeeping is required to maintain a safe
environment around the shakers. Longer stroke lengths also tend to reduce
screen life.

Deck Angle

Because linear motion shakers will convey uphill, most provide an easily-adjust-
able deck angle feature to optimize fluid throughput capacity and cuttings convey-
ance velocity. Uphill deck angles also provide protection against overflow due to
surges at the flow line.

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Figure 3.8 Shaker Throughput vs. Vibrator Frequency. Shaker throughput improves as fre-
quency decreases.

At deck angles greater than 3°, solids grinding in the pool region can be a prob-
lem. Although fluid throughput increases with uphill deck angle, cuttings convey-
ance decreases. Solids conveyance within the pool region is slower than out of
the pool due to viscous drag forces and the differential pressure created across
the cuttings load by the hydrostatic head of the fluid. If the deck angle is too high,
a stationary mound of solids can build up in the pool even though conveyance is
observed at the discharge end (Figure 3.9). The vibrating action of the screen and
extended residence time will tend to grind soft or friable cuttings before they have
the opportunity to be conveyed out of the pool. This condition should be avoided
since the generation of fines in the mud is definitely not desired.

To check for this problem, observe the feed end of the shaker at a connection
immediately after circulation is stopped. There should not be a disproportionate
amount of solids accumulated at the feed end. The problem can be rectified by
lowering the deck angle until the solids mound is eliminated.

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Figure 3.9 Solids Bed Buildup. This may occur when the shaker deck is tilted up too high.

Screen Fastening and Support

The type of screen panel dictates the type and amount of support and fastening
system necessary. The screen fastening and support structure provide the follow-
ing functions:

1. Prevent leakage past the screens

2. Expedite screen replacement

3. Provide even tension on screens to extend screen life

The two types of screen panels are commonly labelled as “pretensioned” and
“nonpretensioned” panels. However, these terms do not exactly describe their
construction since many nonpretensioned panels are, indeed, pretensioned. The
terms “rigid frame” and “hookstrip” more correctly differentiate the two main panel
types.

Hookstrip Screen Panels

This is the most common type of panel, consisting of one to three layers of screen
cloth. The cloth is frequently bonded to a thin perforated-metal grid plate or a plas-
tic grid. Figure 3.10 shows the construction of a typical hookstrip screen. The

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screen panel is tensioned on the shaker deck by an interlocked hookstrip and

drawbar arrangement located on both sides of the shaker (Figure 3.11). Three or
more tensioning bolts are used to pull each drawbar down and towards the side of
the basket. This seats the screen on the shaker deck and distributes even tension
along the hookstrip.

Figure 3.10 Typical Hookstrip Screen. The backing grid, though not necessary, provides support
and improves screen life.

Figure 3.11 Hookstrip Screen Tensioners. This is the most common type of fastening system
for hookstrip screens.

These panels are not rigid; the shaker deck must be crowned to maintain
screen-to-deck contact throughout the vibration cycle. Support ribs in the shaker

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deck are designed to ensure even support of the screen across the width of the
basket. Full contact with all support stringers is critical, especially with
metal-backed panels. The panels will suffer premature fatigue failure if flexing is
allowed to occur.

Because screen tension is extremely important to ensure good screen life, the
tension should be checked frequently on nonpretensioned hookstrip-style
screens. Spring-loaded tensioning bolts are recommended to aid in preventing a
complete loss of tension and premature failure as the screens stretch and “seat”
onto the deck. Tensioning springs are not required for hookstrip panels with metal
backing plates since these panels will not normally stretch.

The crowned deck can cause uneven fluid coverage (Figure 3.12). The mud may
extend further out along the sides of the shaker than at the center where maxi-
mum deck height occurs. This reduces the effective screening area of the shaker,
especially at low deck angles. It can lead to whole mud losses at the discharge
and contribute to unacceptably wet cuttings even though the fluid endpoint along
the centerline of the shaker may be well back from the discharge. The problem
can be mitigated by increasing the deck angle and selecting high efficiency
screens to reduce fluid coverage area.

Screen replacement time is usually much longer than with rigid frame panels.
However, Derrick has developed a new tension bolt design which has improved
screen changing on their Flo-Line Cleaner; the tensioning nut and spring have
been replaced by an integral nut and spring assembly which requires a half-turn to
fully operate.

Rigid Frame (Pretensioned) Screen Panels

In rigid frame screen panel construction, the screen cloth is tensioned and bonded
to an integral steel frame; no additional tensioning is required. Because rigid
frame screens are flat, uneven fluid coverage on the shaker is not a problem. All
other factors being equal, discharged cuttings dryness is reported to be superior
to shakers with hookstrip screen designs.

Since no tensioning is required during installation, the fastening system can be

designed for fast panel replacement. For example, each panel on the Fluid Sys-
tems Model 500 is held in place by two wedges (one on each side). A tap on the
wedge locks the panel in place. The Thule VSM100 has a pneumatically-actuated
system. Sweco's LF-3 Oil-Mizer and Brandt's ATL-1000 also have quick-release
fastening systems.

The two most common types of pretensioned panels are shown in Figure 3.14
and Figure 3.13.

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Figure 3.12 Shaker Fluid Endpoints. Crowned decks will cause uneven fluid coverage espe-
cially at low deck angles.

1. The screen cloth is tensioned and glued directly to the steel frame. Addi-
tional glue lines may be included between the frame members to provide
additional support. The bonding pattern divides the panel into 3- to 4-in. wide
strips oriented parallel to the flow. This design is used in the Fluid Systems
Model 500.

This panel design maximizes usable screening area. However, the large
unsupported area normally limits cloth selection to the heavier grades with
lower flow capacity. The panel is not normally considered repairable.

2. Alternatively, the screen cloth may be bonded to a perforated metal backing

plate similar to a hookstrip screen. The metal backing plate is then bonded to
the support frame to create a rigid panel. The Brandt ATL-1000 and the Thule
VSM-100 use this type of panel.

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Figure 3.13 Rigid Screen Panel with Perforated Plate. The metal grid is bonded to a steel frame.

Usable screen area is reduced by the perforated plated design, but this is off-
set by the option of using higher conductance screen cloth, repairability, and
better screen life under high solids loading conditions.

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Figure 3.14 Rigid Screen Panel. The screen cloth is glued directly to a steel frame.

Three Dimensional Screens

In recent years three dimensional screens have been introduced to the oil
industry. This wave design increases the area of the screen by 40% over the
flat screens. This increase in conductance is only relevant if the screen is
completely submerged in drilling fluid. This reportedly increases the shaker
capacity and allows for finer screening. A picture of a three dimensional
screen is shown in Figure 3.14a.

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Single Deck Shakers

As the name implies, a single deck shale shaker has one discrete screening layer;
the mud and solids fed to the shaker are screened once. One or more screen pan-
els may be used to provide a continuous screening surface. Deck profiles of sin-
gle deck linear motion shakers are usually flat from feed to discharge, but other
profiles are used. For example, the panels of the Fluid Systems Model 500 and
Swaco ALS are arranged in a stairstep pattern: Each downstream panel is slightly
lower than the upstream panel, primarily for ease of panel positioning. Unbal-
anced elliptical motion shakers, such as the Derrick Standard or Swaco Super
Screen, have an increasingly negative (downhill) slope on downstream panels to
improve solids conveyance.

Single deck shakers provide the advantage of allowing complete access to the
screening surface. This simplifies maintenance, panel changes, screen inspection
and cleaning. The disadvantage of single deck shakers becomes apparent under
high solids loading conditions; flow capacity, cuttings dryness and screen life may
be greatly reduced. These problems can be circumvented by using a cascading
shaker arrangement. (Refer to the following section: Cascading Shaker Systems.)

Linear motion single deck shakers are preferred for most applications because of
their simplicity, high flow capacity and fine-screening capability. Their popularity
has spurred numerous companies to manufacture linear motion shakers. A com-
plete list is provided in Appendix E, Equipment Specifications. Many of the major
manufacturers’ shakers have been evaluated in laboratories. Differences in over-
all performance were found to be relatively minor. Examples of single deck linear
motion shakers that will provide acceptable performance are pictured in Figures
3.15-3.20. The shakers are listed in alphabetical order, no ranking is implied by
the order of their appearance.

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Figure 3.15 Derrick Flo-Line Cleaner Plus.

Figure 3.16 Fluid Systems Model 500

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Figure 3.17 Swaco ALS

Figure 3.18 Sweco LF-3 Oil-Mizer

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Figure 3.19 Sweco LM-3

Figure 3.20 Triton NNF

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Cascading Shaker Systems

“Cascading” refers to the use of shakers in series (the mud passes sequentially
through two shakers) to remove drill cuttings in two stages. The first set of shakers
remove or “scalp” the coarsest cuttings from the returned drilling fluid. The mud
and fine cuttings are then fed to a second set of shakers with finer screens. This
arrangement increases the capacity of the fine screen shakers through reduced
solids loading. This arrangement is especially effective when drilling fast, large
diameter hole sections or gumbo formations.

Figure 3.21 illustrates a “2 over 3" cascading shaker arrangement. This arrange-
ment usually provides adequate shale shaker solids removal for drilling most
17-1/2-in. diameter holes. It is important to ensure that valves are provided to iso-
late each shaker in the system as required for screen maintenance and shaker
repair.

Figure 3.21 Cascading Shaker System

In most instances, unbalanced elliptical or circular motion shakers are the pre-
ferred scalping devices. Soft, sticky cuttings such as gumbo are generally handled
better by these vibration patterns with a flat or downhill deck angle. However, lin-
ear motion shakers have been successfully used as scalpers when the deck angle
is steeply pitched downhill (such as a Derrick Standard) or when the deck length
is short (such as the Fluid Systems two-panel shaker).

Because the scalping shakers must be positioned above the fine screen shakers,
sufficient height between the flow nipple and the scalping shaker weirs must be

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available to avoid solids settling in the return line. A good “rule of thumb” is 1 ft of
drop per 12 ft of flowline. Also, additional space is obviously necessary to accom-
modate a cascading system.

Unitized Cascading Systems

A unitized cascading system incorporates two shakers, one stacked over the
other, on a single skid. This design reduces many of the plumbing problems and
costs normally associated with retrofitting a cascading system on a rig. Also, the
unitized system takes up less floor area than a standard cascading system.
Because the top and bottom shaker are separate units, each can be designed for
its specific function without severely impeding screen panel access or perfor-
mance. This is an advantage over integral tandem deck shakers.

There are two disadvantages to unitized cascading systems: (1) They have high
weirs which will limit their application to rigs with sufficient elevation difference
between the flow nipple and the upper shaker weir; and (2) the upper shaker may
be too high to be worked on easily. A permanent walkway or ladder should be
installed to improve access to the upper shaker’s screens.

Two systems are currently available: The Brandt ATL-CS (Figure 3.22) and the
Fluid Systems Model 50-500. The Brandt is a tandem deck, circular motion basket
over a linear motion basket. The Fluid Systems version uses a short, two-panel
linear motion basket as the scalping shaker over their standard Model 500 shaker.

Integral Tandem Deck Shakers

These shakers incorporate two distinct screening decks stacked in a single bas-
ket. The top deck screen “scalps” off the coarse solids to reduce the solids loading
to the lower screens.

Tandem deck shakers are available in both circular and linear motion designs.
The superior fluid processing and finer screening features of linear motion shak-
ers are preferred. In either case, flow back pans are recommended to improve
throughput.

Tandem deck shakers offer a compromise between a true cascading system and
single deck shakers. If the top scalping deck covers the entire basket width, solids
handling capacity is good. However, accessibility to the lower deck screens and
the ability to monitor screen wear is limited. Conversely, a small scalping deck lim-
its solids loading capacity, but improves accessibility and screen monitoring. Tan-
dem deck shakers are recommended for medium-high solids loading applications
or where space or height limitations will not permit the use of a cascading shaker
system.

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The total combined area of both screening surfaces cannot be used to compare
the performance of these shakers to single deck shakers. The relative processing
capacity of tandem deck shakers will depend upon the size distribution of the sol-
ids in the feed, solids generation rate and other factors. Generally, tandem deck
shakers will outperform single deck shakers when large diameter hole and high
penetration rates are encountered. Examples of linear motion tandem deck shak-
ers are shown in Figures 3.23-3.25.

Figure 3.22 Brandt ATL-CS. This is one example of a “unitized” cascading shaker arrangement.

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Figure 3.23 Brandt ATL 1000

Figure 3.24 Derrick Cascade System

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Figure 3.25 Thule VSM 100

Shaker Manifolds

The flowline and manifold system must be designed to provide an even distribu-
tion of mud and cuttings to the shakers. The flow line must have sufficient drop to
prevent solids from accumulating in the line: A drop of 1 ft per 12 ft of run is a
good rule of thumb. Flowline diameter must also be sufficient to handle the maxi-
mum anticipated circulation rates. Diameters of 10 or 12 in. are usually sufficient.

Manifolding can be a problem when three or more shakers are arranged in paral-
lel. Because the shaker feed is essentially two-phase, liquid being one phase and
solids the other phase, equal division of both phases can become difficult to
achieve with typical manifold designs (Figure 3.26 and Figure 3.27). Branch tees
should be avoided. The solids will preferentially travel a straight path, resulting in
uneven solids loading to the shakers. Dead end tees will distribute the solids more
evenly. Examples of recommended manifold designs for multi-shaker installations

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are provided in Figure 3.28, Figure 3.29, and Figure 3.30. Overhead or circular
manifolds will provide better distribution of mud and solids.

All shakers should be level with equal weir heights to ensure even flow distribu-
tion. A common shaker box (possum belly) is acceptable for scalping shakers. It is
not recommended for the fine screen shakers since a large shaker box only
serves to collect solids, which can enter the mud tanks if the bypass gate is
opened.

Figure 3.26 Poor Manifold Design. Distribution to the shakers may be uneven.

Operating Guidelines

Optimizing Screen Life

Perforated plate screens usually exhibit longer screen life than other hookstrip
screens. They provide the most support and are repairable.

1. Screen life is inversely proportional to plate opening size. If premature wear is

apparent in the pool region, install panels with smaller perforated plate sizes
at the feed end of the shaker where loading and wear is greatest.

2. Reduce deck angles to improve solids conveyance, reduce loading and elimi-
nate solids grinding at the feed end.

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Figure 3.27 Better Manifold Design. There are less branch tee’s in this design.

Figure 3.28 Best Conventional Manifold Design. All branch tee’s are eliminated.

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Figure 3.29 Circular Manifold Design. Useful for odd number of shakers. Flowline lengths are
exaggerated.

3. If premature backing plate failure is experienced, check that all deck rubbers
are in place and in good condition. Check for a buildup of solids between the
screen and the support areas on the shaker deck.

Screen Selection

1. When possible, run the same screen mesh over the entire deck of a single
deck shaker. When running different mesh cannot be avoided, the coarser
mesh should be run at the discharge end. Do not vary the mesh size by more
than one increment from feed to discharge.

2. Select the finest screens which will give 70-80% fluid coverage on the shaker
(Exception: See cuttings dryness discussion).

3. Always run the coarser screens on the top deck of a tandem deck shaker or
on the upstream shaker. The upper deck screen should be at least two mesh
sizes coarser than the bottom deck. It has been observed that running
screens which are too fine on the top deck can actually impede cuttings con-
veyance on the lower deck.

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Figure 3.30 Overhead Manifold Design. Excellent for even distribution of liquid and solids, but
more complicated to fabricate.

4. Select screens for which the new API designations are known to ensure pre-
dictable performance.

Cuttings Dryness

The volume of drilling fluid lost with the discharged cuttings is becoming more
important in the wake of increasingly stringent environmental regulations and
more expensive drilling fluid formulations. In most cases, minimizing liquid waste
from the shale shakers makes both economic and environmental sense. A field
procedure to determine composition of the discharge is given in Appendix C, Sol-
ids Control Equipment Discharge Analysis, Oil-Based muds.

Shaker discharge dryness is heavily dependent upon the size distribution of the
cuttings and the viscosity of the mud. There will always be an irreducible “volume
fraction” of fluid wetting the cuttings and this will vary inversely with particle size.
Extremely fine solids have substantially higher percentages of associated liquid
than larger solids due to surface area and surface tension effects. Mud viscosity
will also impact the thickness of this fluid layer.

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 Shale Shakers

The shaker can remove a portion of this residual wetness by the acceleration and
impact forces imparted on the cuttings after they exit the pool region. Dryness
may depend on the magnitude of these forces and the exposure time.

Since a substantial portion of the shaker screening area can be covered by the liq-
uid pool to achieve a desired separation, the remaining dry screening area may
not be sufficient to remove excess moisture carried with the cuttings. High solids
loading rates will also have a negative impact on cuttings dryness.

Solids loading and dry screening area can be addressed during the planning
phase by ensuring that sufficient shaker area is available to maximize cuttings
dryness. The following remedial actions may help improve cuttings dryness:

1. Deck Angle Increase - This is the most simple solution. Fluid loss along the
hookstrips is reduced. Solids conveyance will decrease with steeper deck
inclinations, which increases the contact time to remove excess moisture.
Protection against whole mud losses due to flowline surges is also improved.
The reduction in fluid coverage is not necessarily proportional to the deck
angle selected. Because conveyance is lessened, the solids remain in the
pool longer and can interfere with the ability of the fluid to pass through the
screen, especially at higher solids loading rates. This may retard the forma-
tion of a shorter, deeper pool. Also, solids grinding may become a problem.

2. High Efficiency Screens - Screens with high transmittance values will reduce
fluid coverage and increase dry screening area. Two new screens, the Derrick
“Pyramid” and Cagle’s “HCR” series offer distinct advantages in this applica-
tion. The corrugated “Pyramid” design may reduce mud loss along the hook-
strips and offers increased screening area. Cagle’s HCR cloth has very high
transmittance values and has exhibited service life up to 4 times standard DX
designs.

3. Coarser Screens - This has two effects. First, the fluid endpoint on the shaker
will recede, and second, the average discharged cuttings size will increase.
However, this action usually carries with it the penalty of poorer separation
efficiency and higher costs, unless downstream solids removal equipment
“picks up the slack.” Try running a coarser screen at the discharge end before
converting the entire deck to coarser screens. There are special consider-
ations worth mentioning depending upon the mud system in use:
Unweighted Muds

The importance of fine screening in unweighted muds is typically not as criti-

cal, provided: 1) sufficient hydrocyclones and centrifuges are used, and 2) the
cuttings are not soft and easily degraded by centrifugal pumps. In fact, signifi-
cant fluid savings in oil-based muds have been realized by running coarser

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Solids Control Manual

screens on the shakers to produce a dry discharge and transferring a greater

share of the solids removal to the downstream centrifuges.

Weighted Muds

In weighted muds, the importance of the shaker in the solids removal system
generally precludes the option of running coarser screens. Economics usually
dictate that the finest separation possible be made by the shaker without sub-
stantial loss of barite in the discharge. Drill cuttings missed by the shaker will
remain in the circulating system and eventually contribute to a low gravity sol-
ids buildup and subsequent viscosity increase.

4. G Force Increase - Increased shaker acceleration will help remove excess liq-
uid by overcoming part of the surface tension forces which bind the fluid to the
cuttings. Conversely, cuttings conveyance velocity will increase and screen
life will decrease. Conveyance velocity can be reduced by increasing the deck
inclination, but screen life will decline considerably at accelerations above
4 Gs.

Sticky Solids (Gumbo)

1. Use scalping shakers ahead of fine screen shakers. Circular or unbalanced
elliptical motion shakers or shakers with short basket lengths are recom-
mended as the scalping shakers. If space is limited, tandem deck linear
motion shakers may be used.

2. Use downhill or flat deck angles. Gumbo will not convey well uphill.

3. Gumbo will not stick as persistently to wet screens. When spray bars are nec-
essary to keep the screens wet, use low flow rate nozzles which produce a
fine mist with an umbrella or fan-shaped discharge. These nozzles operate at
less than 0.5 gpm. No more than two are normally required. Do not use high
volume or high pressure sprays on a continuous basis. This will degrade the
gumbo patties and drive the solids through the screens.

Polymer Muds
1. Prehydrate and preshear the polymer before adding into the active mud sys-
tem to eliminate “fish-eyes” and blinding at the shaker.

2. Select high efficiency screens to maximize the flow capacity of the shakers.

3. Expect an overall reduction in shaker flow capacity of as much as 40%.

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 Shale Shakers

Blinding, Plugging
1. Gilsonite (Asphaltenes)
Triple-layer screens are susceptible to plugging by gilsonite or other asphalt-
ene-based products in the drilling fluid. The problem may be mitigated by
selecting single or double-layer screens. For example, on Derrick Flo-Line
Cleaners, use the PBP HP or GBG HP series. Refer to Appendix D, Screen
Designations, for a complete list of screen panel descriptions.

2. Sand (Near Size)

- Unbonded triple layer screens provide the best resistance to blinding, but
screen life is generally poor.
- Single layer, square mesh cloth is most susceptible to blinding. Select
screen series with aspect ratios greater than 1.4. (Refer to Chapter 4,
Shaker Screens.)
- If excess shaker capacity is available, try running a finer screen. The
sands may have a relatively narrow size distribution which might not blind
a smaller opening size.

Lost Circulation Material

1. Do not bypass the shakers to avoid screening out the LCM material.

2. Scalping shakers can be used to recover LCM when high concentrations are
continuously required in the mud, provided:
- Cuttings size distribution is sufficiently fine to pass through the scalping
screens.
- Solids loading rates do not negatively impact the performance of the
downstream shakers and cause solids buildup in the active system.
- The LCM removed by the scalpers is returned to the active system down-
stream of the centrifuge.

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Solids Control Manual

Estimating Number of Shakers Required

1. Base the number of shakers required on the economics and the physical con-
straints of the specific application.

2. A “ballpark” estimate of shaker requirements, based on average drilling condi-

tions can be made from Table 3.1. This is a very rough estimate and should
be used only as a guide.

Table 3.1 Shakers Required

Approximate Number of High Performance
Linear Motion Shakers
Maximum Viscosity (cP)
5 10 15 20 25 30 40 50 60
300 1 1 1 1 1 1 2 2 2
400 1 1 1 2 2 2 2 2 2
500 1 1 2 2 2 2 3 3 3
1 2 2 2 2 3 3 3 3
Circulation Rate (gpm)

600
700 2 2 2 2 3 3 3 3 4
800 2 2 2 3 3 3 4 4 4
900 2 2 3 3 3 4 4 4
1000 2 2 3 3 4 4 4
1100 2 3 3 4 4 4
1200 2 3 3 4 4
1300 2 3 4 4
1400 2 3 4

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 Shale Shakers

Summary

• The shale shaker is the only solids control device that makes a separation
based on the physical size of the particle. The separation size is dictated by
the opening sizes in the shaker screens. Hydrocyclones and centrifuges sep-
arate solids based on differences in their relative mass and the fluid.

• Shale shakers with linear vibratory motion are preferred for most applications
because of their superior processing capacity and fine-screening ability. Cir-
cular motion or unbalanced elliptical motion shakers are recommended as
scalping shakers in cascading systems.

• Vibration of the shaker basket creates G-forces which help drive shear thin-
ning fluids such as drilling mud through the screens. Vibration also conveys
solids off the screens. Most linear motion shakers operate in the range of 3 to
4 G’s to balance throughput with screen life. G-force is a function of vibration
frequency (rpm) and stroke length.

• “High-speed” should not be equated with “high performance.” Laboratory tests

indicate that, in the normal operating range for linear motion shale shakers,
lower frequency vibration and longer stroke lengths improve throughput
capacity. Most linear motion shakers operate at 1200 to 1800 rpm.

• Avoid deck inclinations above 3°. High deck angles reduce solids conveyance
and increase the risk of grinding soft or friable solids through the screens.

• Shakers are designed to accept either hookstrip or rigid frame screen panels.
Hookstrip screen panels are the most common and are usually cheaper,
although cuttings wetness can be a concern due to deck curvature. Flat, rigid
frame panels promote even fluid coverage, but can cost more.

• Shakers may have single or tandem screening decks. Single deck shakers
offer mechanical simplicity and full access to the screening surface. Single
deck shakers may be arranged to process mud sequentially as a “cascading”
system to improve performance under high solids loading conditions. Tan-
dem deck shakers offer improved processing capacity under high solids load-
ing conditions when space is limited.

• Manifolds should provide even distribution of mud and solids to each shaker.
Avoid branch tee’s. Recommended manifold designs are illustrated.

• Operating guidelines are provided for optimizing screen life and cuttings dry-
ness, handling sticky solids, polymer muds, blinding and LCM problems.

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