Solid Control Equiment Shale Shakers Separation by Vibratory Screening

Sept. 19, 2012 - PRLog -- One method of removing solids from drilling mud is to pass the mud over the surface of a vibrating screen. Particles smaller than the openings in the screen pass through the holes of the screen along with the liquid phase of the mud. Particles too large to pass through the screen are thereby separated from the mud for disposal. Basically, a screen acts as a “go-no-go” gauge:  Either a particle is small enough to pass through the screen or it is not.

Screening Surface. Screening surfaces used in solids control equipment are generally made of woven wire screen cloth, in many different sizes and shapes. The following characteristics of screen cloth are important in solids applications.

Screens may be constructed with one or more LAYERS. NON-LAYERED screens have a single screen cloth mounted in a screen panel. These screens will have openings that are regular in size and shape. LAYERED screens have two or more screen cloths, usually of different mesh, mounted in a screen panel. These screens will have openings that vary greatly in size & shape.

Mesh is defined as the number of openings per linear inch. Mesh, can be measured by starting at the center of one wire and counting the number of openings to a point one inch away.

SIZE OF OPENING is the distance between wires in the screen cloth & is usually measured in fractions of an inch or microns.

Screens of the same mesh may have different sized openings depending on the diameter of the wire used to weave the screen cloth.

The smaller the diameter of the wire results in larger screen openings allowing larger particles to pass through the screen. The larger the diameter of the wire, the smaller the particles that will pass through the screen Remember: It is the size of the opening in a screen not the mesh count that determines the size of the particles separated by the screen.

PERCENT OF OPEN AREA: is the amount of the screen surface, which is not blocked by wire. The greater the wire diameter of a given mesh screen, the less open space between the wires. For example; a 4 mesh screen made of thin wire has a greater percent of opening than a 4 mesh screen made of thick wire.

The open area of a non-layered, square or oblong mesh can be calculated and should be available from your screen supplier.

Vibrating Mechanism
The purpose of vibrating the screen in solids control is to tumble the solids particles to separate fluids from solids and increase through put capacity. This vibrating action causes rapid separation of whole mud from the oversize solids, reducing the amount of mud lost with the solids.

For maximum efficiency, the solids on the screen surface must travel in a predetermined pattern. For example; some devices use elliptical motion and others use Linear motion to increase efficiency. The combined effect of the screen and vibration, result in the separation and removal of oversized particles from drilling mud.


Shale Shakers
The first line of defense for a properly designed solids control system has been and will continue to be, the shale shaker. Without proper screening of the drilling fluid during this initial removal step, reduced efficiency and effectiveness of all downstream solids control equipment in the system is assured. The downstream hydrocyclones will simply be overloaded beyond their designed capacity.

The shale shaker, in various forums has played a prominent role in solids control systems for several decades. The two main shale shakers utilized in the utility industry are:

1.         Elliptical,         “unbalanced” design

2.         Linear             “straight line” design


Shale Shaker Maintenance
Because of their greater efficiency & complexity the use of finer mesh screens is essential. This requires more attention than the standard scalping shale shaker screen.

Besides periodic lubrication, fine screen use requires the following care:

Wash down screens with power washer regularly

Check screens for tear or rips

Make sure screens are properly mounted

Make sure shaker is at proper angle

Check wiring or a regular basis high speed shakers tend to wear through wiring insulation

In addition, frequent checks must be made for plugging or blinding screens.  The shaker angle can be increased or decreased to help eliminate this problem. For blinding screens a more coarse or finer screen may be installed to help solve the problem.

Remember your shale shaker is your first line of defense in your solids control system, Choose a shale shaker that is correct for your application and have rig personnel learn to use it correctly.

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