Shale shakers

Typical Shale Shakers on a drilling rig

Shale shakers are components of drilling equipment used in many industries, such as coal cleaning, mining, oil and gas drilling.[1][2] They are the first phase of a solids control system on a drilling rig, and are used to remove large solids (cuttings) from the drilling fluid ("Mud").

Drilling fluids are integral to the drilling process and, among other functions, serve to lubricate and cool the drill bit as well as convey the drilled cuttings away from the bore hole. These fluids are a mixture of various chemicals in a water or oil based solution and can be very expensive to make. For both environmental reasons and to reduce the cost of drilling operations, drilling fluid losses are minimized by stripping them away from the drilled cuttings before the cuttings are disposed of. This is done using a multitude of specialized machines and tanks.

Shale shakers are the primary solids separation tool on a rig. After returning to the surface of the well the used drilling fluid flows directly to the shale shakers where it begins to be processed. Once processed by the shale shakers the drilling fluid is deposited into the mud tanks where other solid control equipment begin to remove the finer solids from it. The solids removed by the shale shaker are discharged out of the discharge port into a separate holding tank where they await further treatment or disposal.

Shale shakers are considered by most of the drilling industry to be the most important device in the solid control system as the performance of the successive equipment directly relates to the cleanliness of the treated drilling fluid.

Mudloggers usually go out and check the shakers for rock samples that have circulated from bottom. They separate the rock from the drilling fluid and take it into an onsite lab where they dry out the samples and label them according to depth. They then look at the samples and analyze what kind of rock they have at a certain depth. This helps determines what depth that type of rock was encountered.

Structure

Shale shakers consist of the following parts:

Oil well Shaker
Some feeders can be equipped with a bypass valve at the bottom of the feeder which allows the drilling fluid to bypass the shaker basket and go directly into the hopper and back into the mud system without being processed by the shaker screens.
New Shale Shakers
As a rule of thumb the Beach and pool are maintained at a ratio of 80% pool and 20% beach, this of course can change depending on the requirements of cutting dryness and flow rates.
There are various angling mechanisms currently in use which vary from hydraulic to pneumatic and mechanical, they can be controlled from either one side of the shaker or must be adjusted individually per side. Mechanical angling mechanisms can be very dependable often requiring less maintenance but usually take more time to operate than their hydraulic or pneumatic counterparts where as the hydraulic/pneumatic angling mechanisms are much faster to operate and require less a physical means of operation.
Mudloggers collecting samples out of the shakers
Some shakers come with an optional third motor on the shaker bed, this motor is most often used to modify the elliptical motion of the basket making it more circular therefore "soften" the motion, but comes at a cost of decreased G's and slower conveyance of the cuttings. This motion is usually used for sticky solids.NOV Brandt VSM 300 shale shaker is the world’s first balanced elliptical motion shaker.[3]

Shaker screen panels

A shaker screen consists of the following parts:

Oil Rig Shaker

*Screen Frame- Much like a canvas for painting a screen has to be supported on a frame in order to do its job, this frame differs between manufacturers in both material and shape. Screen frames can be made from materials such as, square steel tubing, flat steel sheets, plastic type composites or they can just be supported on the ends with strips of steel (similar idea to a scroll). These frames consist of a rectangular shaped outer perimeter which is divided into small individual inner panels. These smaller panels differ in shape from manufacturer to manufacturer and have been known to come in shapes such as square, hexagonal, rectangular and even triangular.

These differing panel shapes are used in an attempt to reduce the quantity of panels on each frame but still provide maximum rigidity and support for the mesh attached to them. The purpose of reducing these panels is to maximize usable screening area as the walls of each panel get in the way of the mesh and prevent it from being used, this is known as "blanking". The non-blanked screening area of a shaker screen is widely used as a selling feature, the more screen surface you have available to work the more efficient your shaker becomes and therefore can handle a higher quantity of fluid.
To maximize screen life most manufacturers build their screens with multiple layers of mesh over a very sturdy backing cloth to further protect the cloth against solids loading and wear. The multiple layers of mesh act as a de-blinding mechanism pushing near sized particles, which may get stuck in the openings, out of the mesh reducing blinding issues and keeping the screen surface available for use.
Plastic composite screens tend not to use adhesives but rather heat the mesh and melt it into the screen frame to form a bond.
There are many claims in regards to the reason for the improved performance of these 3D screens such as:
  • Increasing the screening area of each panel transfers the load across more surface area and therefore the wear tends to be decreased in comparison to other screens.
  • The corrugated shape of the screens encourages solids to settle in the valleys of the screen, keeping the peaks of the screen available to process drilling fluid.
  • The tapered valleys, while moving under high G's, apply a compression force on the solids similar to wringing out a cloth to draw out liquid.
  • Increasing the surface area of the shaker allows the use of finer screens earlier in the drilling process while maintaining acceptable flow rates and penetration rate. Effectively removing harmful drilled solids before they can begin to wear out the solids control equipment.

Although the performance of these screens is quite impressive the only way to truly gauge the performance of any screen is to try it out and collect comparative data of your own.

Causes of screen failure

The causes of premature screen failure are:

API standards

API Standard Screen Identification

The American Petroleum Institute (API) Screen Designation is the customary identification for screen panels. This includes:

References

China Drilling Mud Shale Shaker

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