SHAKER SCREEN CLOTHS

Shale shakers remove solids by processing solids-laden drilling fluid over
the surface of a vibrating shaker screen. Particles smaller than the shaker screen openings pass through the screen along with the liquid phase of the drilling fluid.

 

Larger particles are separated into the shaker overflow for discard.
The shaker screen acts as a ‘go no-go’ gauge. That is, particles larger than
the screen openings remain on the screen and are discarded. Particles
finer than the screen openings go through the screen with the drilling
fluid. The criterion for early shale shaker screens was a long screen
life. This demand for screen life was consistent with the shaker designs
and solids-removal philosophies of the time period. Early shale shakers
could remove only large solids from the drilling fluid. The sand trap,
reserve and settling pits, and downstream hydrocyclones (if utilized)
removed the bulk of drilled solids. Today’s shale shakers are capable
of utilizing finer screens that remove more solids. Desirable characteristics
for a shaker screen are:
1. Economical drilled-solids removal
2. Large liquid flow rate capacity
3. Plugging and blinding resistance
4. Acceptable service life
5. Easy identification
For any particular shale shaker, the size and shape of the shaker screen openings have a great effect on solids removal. This means that the performance of any shaker is largely controlled by the screen cloth used.
The first four items in the preceding list are largely controlled by
choice of screen cloth and by the screen panel technology. Large gains
in shale shaker performance are a direct result of improved screen
cloth and panel fabrication. shaker Screens used on shale shakers have evolved into complex opening patterns.

 

SHALE SHAKER USER’S GUIDE

Every solids-removal system should have enough shale shakers to process 100% of the drilling-fluid circulating rate. In all cases, consult the owner’s manual for correct installation, operation, and maintenance 154 Drilling Fluids Processing Handbook procedures. If an owner’s manual is not available, the following general guidelines may be helpful in observing proper procedures.

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DRYER SHAKERS

The dryer shaker, or dryer, is a linear motion shaker used to minimize the volume of liquid associated with drilled cuttings discharged from the main rig shakers and hydrocyclones. The liquid removed by the dryers is returned to the active system.

Why use dryer shaker

Dryers were introduced with the closed-loop mud systems and environmental efforts to reduce liquid-waste haul-off. Two methods, chemical and mechanical, are available to minimize liquid discharge. The chemical method uses a system called a dewatering unit, while the mechanical method takes place through linear motion shakers. These systems may be used separately or together.

The main function of drying shaker

The dryer shaker deliquifies drilled cuttings initially separated by another piece of solids-separation equipment. These drilled solids can be discharged from the main shaker or a bank of hydrocyclones. Dryers recover liquid discharged with solids in normal liquid/solids separation that would have been previously discarded from the mud system. This liquid contains colloidal solids, and the effect on drilling-fluid properties must be considered since dewatering systems are frequently needed to flocculate, coagulate, and remove these solids.

The dryer family incorporates pieces of equipment long used as independent units: the main linear motion shaker, the desander, and the desilter, which are combined in several configurations to discharge their discard across the fine screens (e.g., API 200) of a linear motion shaker to capture the associated liquid. These units, formerly used as mud cleaners, are mounted on the mud tanks, usually in line with the main linear motion shaker. They can be tied into the flowline to assist with fine screening when not being used as dryers. Their pumps take suction from the same compartments as desanders and desilters and discharge their overflow (effluent) into the proper downstream compartments.

How to use it

A linear motion dryer may be used to remove the excess liquid from the main shaker discharge. The flow rate across a linear motion dryer is substantially smaller than the flow rate across the main shaker. The lower flow rate permits the removal of the excess fluid by the linear motion dryer by using a finer screen. The dryer is usually mounted at a lower level than the other solids-separation equipment to use gravity to transport solids to it. Whether by slide or by conveyor, the cuttings dump into a large hopper, located above the screen, that replaces the back tank, or possum belly. As the cuttings convey along with the screen, they are again liquefied. This excess fluid, with the fine solids that passed through the screens, is collected in a shallow tank that takes the place of a normal sump. The liquid is pumped to a catch tank that acts as the feed for a centrifuge or back to the active system.

A dryer unit can be used to remove the excess fluid from the underflow of a bank of hydrocyclones (desanders or desilters). This arrangement resembles a mud cleaner system. In this configuration, the dryer unit may be used on either a weighted or an unweighted mud system. The liquid recovered by the linear motion shaker under the hydrocyclones can be processed by a centrifuge, as previously described.

How to select a proper one for your mud solution

The perfection of the linear motion shaker for drilling-fluid use, coupled with advanced fine-screen manufacturing technology, has made these dryers very efficient. In most configurations, the dryers use the same style of screens, motors, and/or motor/vibration combinations as do other linear motion shakers by the same manufacturer.

Depending on the fluid, saving previously discarded liquid may be financially advantageous. The dryer discard is relatively dry and can be handled by backhoe and dump truck rather than by vacuum truck.

Drilling-fluid properties must be monitored properly when the recovered liquid is returned to the active system. Large quantities of colloidal solids may be recovered with the liquid. This could affect the PV, YP, and gel strengths of a drilling fluid.

CASCADE SYSTEMS

Cascade 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 solids. The first cascade system was introduced in the mid-1970s. A scalper shaker received fluid from the flowline and removed gumbo or large drilled solids before the fluid passed through the main shaker with a fine screen. The first unit combined a single-deck, elliptical motion
shaker mounted directly over a double-deck, circular motion shaker (Figure 7.17). This combination was especially successful offshore, where space is at a premium. It was, however, subject to the technology limitations of that time period, which made API 80 to API 120 screens the practical limit.
One advantage of multiple-deck shale shakers is their ability to reduce solids loading on the lower, fine-screen deck. This increases both shaker capacity and screen life. However, capacity may still be exceeded under

Figure 7.17. First cascade shaker system.

many drilling conditions. The screen opening size, and thus the size that
solids returned to the active system, is often increased to prevent loss of
whole drilling fluid over the end of the shaker screens.
Processing drilling fluid through shale shaker screens, centrifugal
pumps, hydrocyclones, and drill-bit nozzles can cause degradation of
solids and aggravate problems associated with fine solids in the drilling
fluid. To remove drilled solids as soon as possible, additional shakers
are installed at the flowline so that the finest screen may be used.
Sometimes as many as 6 to 10 parallel shakers are used. Downstream
equipment is often erroneously eliminated. The improved shale shaker
still remains only one component (though a very important one) of the
drilled-solids removal system.
A system of cascading shale shakers—using one set of screens (or
shakers) to scalp large solids and gumbo from the drilling fluid and
another set of screens (or shakers) to receive the fluid for removal of
fine solids—increases the solids-removal efficiency of high-performance
shakers, especially during fast, top-hole drilling or in gumbo-producing
formations, which is its primary application. The cascade system is used
where solids loading exceeds the capacity of the fine screens, that is,
it has been designed to handle high solids loading. High solids loading
occurs during rapid drilling of a large-diameter hole or when gumbo
arrives at the surface.

The advantages of the cascade arrangement are:
1. Higher overall solids loading on the system
2. Reduced solids loading on fine mesh screens
3. Finer screen separations
4. Longer screen life
5. Lower fluid well costs
There are three basic designs of cascade shaker systems:
. Separate unit concept
. Integral unit with multiple vibratory motions
. Integral unit with a single vibratory motion
The choice of which design to use depends on many factors, including
space and height limitations, performance objectives, and overall cost.

1 Separate Unit

The separate unit system mounts usable rig shakers (elliptical or
circular motion) on stands above newly installed linear motion shakers
(Figure 7.18). Fluid from the rig shakers (or scalping shakers) is
routed to the back tank of a linear motion shaker. Line size and potential
head losses must be considered with this arrangement to avoid overflow
and loss of drilling fluid. This design may reduce overall cost by utilizing
existing equipment and, where space is available, has the advantages of
highly visible screening surfaces and ease of access for repairs.

Figure 7.18. Separate unit cascade system.

2 Integral Unit with Multiple Vibratory Motions

This design type combines the two units of the separate system into
a single, integral unit mounted on a single skid. Commonly, a circular,
elliptical, or linear motion shaker is mounted above a linear motion
shaker on a common skid (Figure 7.19). The main advantages of this
design are reduced installation costs and space requirements. The internal
flowline eliminates the manifold and piping needed for the two separate
units. This design reduces screen visibility and accessibility to the drive
components.

Figure 7.19. Integral cascade unit with multiple vibratory motions.

3 Integral Unit with a Single Vibratory Motion

This design is shown in Figure 7.20. Typically, this device uses a linear
motion shaker and incorporates a scalping screen in the upper part of
the basket. The lower bed consists of a fine-screen, flow line shaker
unit, and the upper scalper section is designed with a smaller-width
bed using a coarser screen. Compared with the other cascade shaker
units, this design significantly lowers the weir height of the drilling fluid
inlet to the upper screening area. Visibility of and access to the
fine-screen deck can be limited by the slope of the upper scalping deck.

4 Cascade Systems Summary

Cascade systems use two sets of shakers: one to scalp large solids gumbo
and another to remove fine solids. Their application is primarily during
fast, top-hole drilling or in gumbo formations. This system was designed
to handle high solids loading. High solids loading occurs during rapid
drilling of a large-diameter hole or when gumbo arrives at the surface.
The introduction of high-performance linear motion and balanced
elliptical shale shakers has allowed development of fine-screen cascade
systems capable of API 200 separations at the flowline. This is particularly
important in areas where high circulating rates and large amounts of drilled solids are encountered. After either the flow rate or solids loading
is reduced in deeper parts of the borehole, the scalping shaker should
be used only as an insurance device. Screens as coarse as API 10 may be
used to avoid dispersing solids before they arrive at the linear motion
shaker. When the linear motion shaker, with the finest screen available,
can handle all of the flow and the solids arriving at the surface, the need
for the cascade system disappears, and the inclination may be to discontinue
the use of the scalping screen unit. Even when the fine screen can
process all of the fluid, screens should be maintained on the scalper
shaker. These screens can be a relatively coarse mesh (API 10 to API
12), but they will protect the finer-screen mesh on the main shaker.
The use of finer screens on the scalping shaker will result in fewer drilled
solids being removed by the scalping and main shakers.

Figure 7.20. Integral cascade unit with single vibratory motions.