Page 130 - Shale Shakers Drilling Fluid Systems

SHAKER APPLICATIONS 113

solids. Their application is primarily during fast, top- The dryer family incorporates equipment long
hole drilling, or in gumbo formations. This system used as independent units: the main linear motion
was designed to handle high solids loading, which shaker, the desander, and the desilter. They are
occurs when rapidly drilling large-diameter holes or combined in several configurations to discharge
when gumbo arrives at the surface. their discard across fine mesh screens of a linear
The introduction of linear motion shale shakers motion shaker to capture the associated liquid.
has allowed development of fine screen cascade These units, formerly identified as mud cleaners,
systems capable of 200-mesh separations at the are mounted on the mud tanks, usually in line
flow line. Scalping screens, as coarse as 10 mesh, with the primary linear motion shaker. They can
may be used to avoid dispersing solids before arriv- also be connected to the flow line to assist with
ing at the linear motion shaker. This is particularly fine screening when not being used as dryers.
important in areas where high circulation rates and Their pumps obtain suction from the same
large amounts of drilled solids are encountered. compartments as desanders and desilters and
After either the flow rate or solids-loading is discharge their overflow into the proper down-
reduced in deeper parts of the bore hole, the scalp- stream compartments.
ing shaker should be used only as an insurance A linear motion dryer may be used to remove
device. When the linear motion shaker, with the the excess liquid from the main shaker discharge.
finest mesh screen available, can handle all of the The flow rate across a linear motion dryer is sub-
flow and solids arriving at the surface, the need stantially smaller than the flow rate across the
for the cascade system disappears. When this oc- main shaker. This lower flow rate permits the use
curs, the inclination may be to discontinue the use of finer mesh screens and removal of the excess
of the scalping screen unit. However, even when fluid by the linear motion dryer. This dryer is usu-
the fine mesh screen can process all of the fluid, ally mounted at a lower level than other solids
screens should be maintained on the scalper shaker separation equipment to allow gravity to transport
for use as needed. These scalping screens can be the solids. Whether using a slide or conveyor, the
changed to a relatively medium-coarse mesh (12 cuttings are deposited into a large hopper located
or 40 mesh) and still be used to protect the finer above the screen that replaces the back tank or
mesh on the main shaker. possum belly. As the cuttings are transported along
the screen, they are again deliquified. This excess
fluid, together with the fine solids that passed
DRYER SHAKERS through the screens, is collected in a shallow tank
that takes the places of a normal sump. This liq-
The dryer shaker, or dryer, is a linear motion uid is pumped to a catch tank, that acts as the
shaker used to minimize the volume of liquid as- feed for a centrifuge, or back to the active system.
sociated with drilled cuttings discharged from the A dryer unit can be used to remove the excess
main rig shakers and hydrocyclones. The liquid fluid from the underflow of a bank of hydro-
removed by the dryers is returned to the active cyclones (desanders or desilters). This arrange-
system. Because of environmental efforts to re- ment resembles a mud cleaner system. When used
duce liquid waste disposal, dryers were introduced in this configuration, the dryer unit may be used
with closed loop mud systems. Two methods on either a weighted or unweighted mud system.
are available to minimize liquid discharge: chemi- The liquid recovered by the linear motion shaker
cal and mechanical. (The chemical system, called under the hydrocyclones can be processed by a
a dewatering unit, is described in Chapter 13.) Lin- centrifuge as previously described.
ear motion shakers are used to mechanically re- The perfection of the linear motion shaker
duce the liquid discard. These systems may be for drilling fluid use, coupled with advanced fine
used independently or in combination. screen manufacturing technology, has made these
The dryer is used to deliquify drilled cuttings dryers very efficient. In most configurations, the
initially separated by another piece of solids sepa- dryers use the same style of screens, motors, and/
ration equipment. These drilled solids can be the or motor/vibration combinations as other linear
discharge from a main shaker or a bank of hydro- motion shakers.
cyclones. Dryers recover liquid discharged with Depending on the fluid, saving previously lost
solids in normal liquid-solids separation that would liquid from the discard may be financially advan-
have been previously discarded from the mud sys- tageous. The dryer discard is relatively dry and,
tem. This liquid contains colloidal solids and the therefore, may be removed with a backhoe and
effect on drilling fluid properties must be consid- dump truck rather than a vacuum truck.
ered since dewatering systems are frequently needed It is important to remember that drilling fluid
to flocculate, coagulate, and remove these solids. properties must be properly monitored when the