BAKER HUGHES - Drilling Fluids Reference Manual

MECHANICAL SOLIDS CONTROL
oil fluids are used, then even centrifuging is not feasible because of economic and environmental
reasons. Dual centrifuging an oil or synthetic is done to strip and clean mud plant fluids In this
case, it is very important to have optimum solids removal at the shale shaker. It would be contrary
to sound engineering practices to spend thousands of dollars for an oil-base fluid system or any
inhibited system to retain “cuttings integrity” without utilizing the most efficient solids control
equipment available. An inhibited system (such as CARBO-DRILL SM or NEW-DRILL ® ) cannot
achieve its full potential and be cost-effective if the cuttings are re-circulated and ground down into
very fine particle sizes.
Two basic designations are used for shakers presently in the field – rig (scalper shaker) and highspeed
shakers. Normal operation of scalper shakers would typically employ the use of screens in
the 10- to 40-mesh range. The removal of large drill cuttings at this stage will increase the
efficiency of the downstream high-speed shakers. The term high-speed refers to a unit that is
capable of operating with fine screens. These units also are commonly referred to as linear motion,
premium, and high-efficiency shakers. The term high-speed had its origin with some of the early
improved shakers that operated with speeds in the range of 3600+ rpm. Although very few shakers
have this speed on the vibrator shaft at present, the term stuck. Linear motion refers to the action
that the vibrating assembly transmits to the screen deck, in this case a reciprocating motion. Figure
10-2 demonstrates three typical screen motions.
Figure 10 - 3 Typical Screen Motions
Regardless of the particulars of the machine, the most important point to remember is that the goal
is to remove the maximum amount of solids, and this is done by running a screen with the smallest
openings. If we assumed the average particle size of formation solids (in fluid returns) was 80%
finer than 838 microns and 70% larger than 178 microns, theoretically only 20% could be removed
with the 20-mesh screen, whereas 70% could be rejected with the 80-mesh screen.
Fine shaker screens come in a multitude of designations, and no single measurement adequately
describes a screen's solids removal capabilities and throughput. Mesh is the linear measurement of
the number of openings per inch. The aperture is the actual opening dimension which controls the
maximum size particle that can pass through a screen. Two screens with the same mesh, if woven
with different diameter wires, will have different apertures.
BAKER HUGHES DRILLING FLUIDS
REVISION 2006 10-8
REFERENCE MANUAL