STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

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692 Drilling and Well Completions
Table 4-55
Drill Cuttings Separation Principles
Method Sortina Mechanisms Characteristics Devices
Adhesion of fines to coarse
Screening Size exclusion solids: High throuput;
Dry underflow
Shakers. Mud cleaners
Gravity forces No shear; Low throuput; Settling tanks
Liquidous underflow
Settling Combination of drag High shear Desanders
and centrifugal High throuput Desilters
forces
Liquidous underflow
Centrifugal forces
Low shear; Low throuput
underflow
Low shear; Low throuput
Liquidous underflow
Decanting centrifuge
Peforated rotor
centrifuge
Solids size, microns
Geological Sediment
Rock
API Bullentin RP 13C
Practical
2 44 74 200 250 2000
Clay Silt Sand Gravel
Shale Siltstone Sandstone Conglomerate
Colloidal Ultra Fine Fine Medium Intermediate Coarse
Clav Silt API Sand or cuttinas
Barites range in size from 2 to 74 pm; its typical size distribution is shown in
Figure 4-1 16 [34]. Also, the API-approved barite should have a minimum specific
gravity of 4.2.
Undesirable solids are drilled cuttings and those solids sloughed into the
borehole. They usually occur in all size ranges from colloidal to coarse. The
specific gravity of commonly encountered drilled solids ranges from 2.35 (shale),
through 2.65 (sand), 2.69 (limestone), to 2.85 (dolomite); see Table 4-57 [29].
Drilled solids include active drilled solids and inactive drilled solids. Clays
and shales are considered to be active drilled solids; they disperse into colloidal
size readily and become detrimental to drilling by increasing the apparent
viscosity and gel strength of the mud. Inactive drilled solids are sand, dolomite,
limestone, etc.; if they occur in colloidal size, these solids may increase plastic
viscosity of the drilling mud.
For all practical purposes, solids in drilling mud are considered to be either
low-gravity solids (drilled solids and gel, SG = 2.5 or 2.6) or high gravity solids
(barite, SG = 4.2).