Page 113 - Shale Shakers Drilling Fluid Systems

96 SHALE SHAKERS AND DRILLING FLUID SYSTEMS

significant effect on both solids and liquid motion shakers, introduced in the 1980s, have be-
capacity. A very small increase in near-size come widely used because of their improved solids
particles usually results in a large decrease conveyance and fluid throughput. Balanced elliptical
in fluid capability for any screen, whether and linear motions make it possible to convey sol-
they be single, double, or triple layer. ids toward the discharge end of the deck while the
screen is tilted uphill. The uphill tilt of the deck
Quantity of solids—Solids compete with the creates a pool of fluid at the feed end of the deck,
liquid for openings in the shaker screen. Fast which, in combination with the balanced elliptical
drilling can produce large quantities of solids. or linear motion, exerts greater pressure on the
Usually, this requires coarser mesh screens to fluid flowing through the screen openings. This
allow most of the drilling fluid to be recov- allows the use of a finer mesh screen than with
ered by the shale shaker. Fast drilling is usu- previous shaker designs. The normal component
ally associated with shallow drilling. The usual of the acceleration controls the liquid throughput.
procedure is to start with a coarser mesh The normal component of a circular and a linear
screen in the fast drilling of larger holes near motion shaker may have the same acceleration (or
the top of the well and to then use finer "G"-factor) but the linear motion shaker can pro-
mesh screens as the well becomes deeper. cess a greater flow rate. The linear motion con-
Finer mesh screens can be used when the veys solids uphill, whereas circular motion does
drilling rate decreases. not. The uphill solids conveyance allows the lin-
Boreholes that are not stable can also pro- ear motion to process a greater flow rate.
duce large quantities of solids. Most of the The use of linear motion shakers has become
very large solids that arrive at the surface feasible with the development of improved screen
come from the side, and not the bottom, of designs. The life of shaker screens has been ex-
the borehole. Drill bits usually create very tended with the introduction of repairable bonded
small cuttings.
and pretensioned screen panels. Other design im-
Hole cleaning—One factor frequently over- provements are available in wire cloth, non-
looked in the performance of shale shakers metallic screens, and three-dimensional screen
is the carrying capacity of the drilling fluid. surfaces, which have improved the solids separa-
If the cuttings are not brought to the surface tion capabilities of all shakers.
in a timely manner, they tend to disintegrate Although linear motion shale shakers have made
into small solids in the borehole. If they stay a significant impact in solids removal concepts,
in the borehole for a long enough period be- the other shale shakers have many advantageous
fore arriving at the surface, the plastic vis- features. Circular motion is easier on the shale
cosity and the solids content of the drilling shaker structure, easier on the shaker screens,
fluid increases. This makes it appear that the and conveys gumbo. Linear motion and elliptical
shale shaker is not performing adequately, motion machines can convey gumbo downhill
when actually the solids are disintegrating but not upward. Linear motion shakers may use
into those that cannot be removed with the bonded screens where 30% to 50% of the area is
shale shaker. forfeited. The liquid pool at the back of the linear
motion screens can cause solids to disintegrate
into many smaller particles and forced through the
SHAKER DEVELOPMENT SUMMARY shaker screens. This liquid pool also gives solids
slightly finer than the screen openings more of a
Shale shakers have undergone many improve- chance to pass through the screen. The various
ments since the last shale shaker handbook was types of motions will be discussed more thor-
published in the early 1970s. The current linear oughly in Chapter 3.