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12 Part I Liquid Drilling Systems

Figure 1.13 A shale shaker (Courtesy of TSC.)

rejected and all smaller pieces pass through. The process of the screen
moving at high vibratory speed prevents many undersized particles from
passing through. Cuttings are not neat round balls, and no perfect
method is available for measuring and stating their size. The median
cut-size particle size is the size of half the particles that pass through and
the size of the half that are rejected. The median particle size is much
smaller than the mesh size for vibrating screens. Square mesh vibrating
screens reject approximately 85 percent of the cuttings of the same size
as the mesh.
Degassers are used to remove gas in the mud that is to be pumped
into desanders using centrifugal pumps. The efficiency of the pumps
drops significantly if gas exists in the mud. Degassers are essential to the
solid-removal process involving viscous mud. Shale shakers can remove a
good portion of the gas from badly gas-cut mud, especially if the yield