Screen Capacity

Screen Capacity, or the volume of mud which will pass through a screen without flooding, varies widely depending on shaker model and drilling conditions. Drilling rate, mud type, weight and viscosity, bit type, formation type, screen mesh — all affect throughput to some degree.

Drilling rate affects screen capacity because increases in drilled solids loading reduce the effective screen area available for mud throughput. The mesh of the screen in use is also directly related to shaker capacity because, in general (but not always), the finer a screen's mesh, the lower its throughput. Increased viscosity, usually associated with an increase in percent solids by volume and/or increase in mud weight, has a markedly adverse effect on screen capacity. As a general rule, for every 10% increase in viscosity, there is a 2-5% decrease in throughput capacity. Figure 3-11 shows the relationship of mud weight, viscosity, and screen mesh on shaker capacity.

INCREASING MUD WEIGHT OR VISCOSITY

Figure 3-11 Shaker Capacity v. Mud Weight, Viscosity, and Screen Mesh

INCREASING MUD WEIGHT OR VISCOSITY

Figure 3-11 Shaker Capacity v. Mud Weight, Viscosity, and Screen Mesh

Mud type also has an effect on screen capacity. Higher viscosities generally associated with oil-base and invert emulsion mud usually result in lower screen throughput than would be possible with a waterbase mud of the same mud weight. Some mud components such as synthetic polymers also have an adverse effect on screen capacity. As a result, no fine mesh screen can offer a standard throughput for all operating conditions.

Due to the many factors involved in drilling conditions, mud characteristics and features of certain models, capacities on fine screen shakers can range from 50 to 800 GPM. Multiple units, most commonly dual or triple units, can be used for higher throughput requirements. Cascade shaker arrangements, with scalping shakers installed upstream from the fine screen shakers, can also increase throughput.

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