Shale Shaker Performance

coarse stainless steel shaker screen

A shale shaker is a vibrating screen used for solid/liquid separation and is the first of several serially connected solids-control devices to process the drilling fluid being from a well. It is a key device in the solids-control system because the efficient operation of other surface solids-separation equipment is critically dependent on proper functioning of the shale shaker. Because no analytical design methods are currently available, shakers with widely varying design parameters are on the market-namely, with deck angles varying from 5° uphill to 30° downhill, normal acceleration from 1. I to 8.3g, screen vibration patterns varying among linear, elliptical, and circular, and vibrator rotary speeds varying from 900 to 3,600 rev/min.

As the drilling fluid containing drilled solids flows onto the vibrating screen, the liquid/solid separation process begins, provided that the screen opening is such that all the solids do not pass through the screen with the liquid.The liquid along the screen disappears through the screen cloth as it reaches a point called the liquid endpoint, but separated wet solids continue toward the discharge end. Strictly speaking, the solids-conveyance problem should be considered before the liquid endpoint. The solids-conveying velocities before and after the liquid endpoint, however, are matched once a steady state is reached. Thus for the sake of simplicity, the solids-conveyance dynamics are thought after the solids pass the liquid endpoint.

Shale Shaker Eliminate Solids from drilling mud

The drilled-solids particles of different shapes and sizes are moving beyond the liquid endpoint from bulk material, or patties, as they stick together because of collision and adhesive forces. Unless the normal acceleration of the sinusoidally vibrating screen can exceed the combined normal acceleration of gravity and adhesion between a wet patty and the screen, the patty can never leave the screen during a vibration cycle.

The expression that relates actual fluid flow capacity of a shaker to its fluid-only flow capacity (no solids) in terms of the solids/screen interference factor and the solids loading factor should prove useful in evaluating the performance of a given shaker.  The average solids-conveying velocity required for determining the loading factor is predicted by the new dynamic conveyance model. The dynamic model provides a method for studying the effect of various shaker parameters on solids conveyance of the screen. It can also help with the optimum design of shale shakers for efficient solids conveyance and maximum fluid handling capacity, within realistic constraints of maximum stroke length and acceleration limits for screen life. Strictly speaking, optimum design should also involve consideration of screen life. Unfortunately, factors affecting screen life are poorly understood and more work is required on this problem. Recent efforts to improve the design of screens, cloth material, and bonding techniques are encouraging. It is possible that uniform elliptical vibration may improve screen life over that for the linear vibration.


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