Page 145 - Shale Shakers Drilling Fluid Systems

128 SHALE SHAKERS AND DRILLING FLUID SYSTEMS
Causes of Premature Screen Failure
Several factors may contribute to premature
screen failure. Most failures result from improper
screen installation or damage to the shaker itself.
Cracked or warped shaker beds, which may result
from many years of continuous use or improper
maintenance, will cause poor vibration patterns.
This may cause improper solids conveyance, which,
in turn, may cause solids to gather on certain
areas of the screen, wearing holes in that section.
Damaged beds may also affect the tensioning abil-
ity of the tension system, inducing flexure in the
screen. This increase in flex causes the screen it-
self to vibrate separately from the basket against
the screen support stringers, damaging the spot on
the screen where this is occurring.
An increase in screen flexure ultimately results
in most cases of early screen fatigue. All screen
tensioning components must be in proper work-
ing order to eliminate screen flexure and maxi-
mize screen life. Some of the screen tensioning
system materials that must be maintained include
the cross and side supports, channel rubbers, and
tension bolts. As prolonged use of the shakers
continues, the support rubbers—rubber liners that
cover the support stringers—will begin to wear. In
order for the support rubbers to tension the screens
properly, they must all be the same thickness;
however, this is rarely the case once these rubbers
begin to wear. Flexure develops in the areas where
the greatest amount of wear has occurred on the
rubbers, reducing the screen life. The side and cross the screens where the accumulation is occurring.
supports—fiberglass strips on which the screens rest This problem may arise, particularly with the three-
along the inside of the shaker bed—will wear in a
similar manner. This interferes with the ability of the Where misalignment occurs, solids tend to accumu-
bolts to apply the proper amount of tension on the
screens, which will again cause loose screens and
rapid failure. Bent steel supports that interlock with veyance, and therefore, screen wear, is the linear
hook strips on the screens to fasten the screens
directly to the shaker bed—will not allow tension
to be applied evenly throughout the full length of
the screen, also resulting in early screen failure.
To achieve maximum screen life, all tension bolts
must be operating properly. If early screen failure
occurs, check to make sure that one or more of
the tension bolts are not missing and that they are
tightened correctly. The tension bolts should be
tightened to manufacturer's recommendations.
Before installing any screens, the shaker bed
must be washed clean of any debris. Proper ten-
sioning of the screen cannot be achieved if any
substance comes between the screen and the bed.
Improper installation or maintenance of the ten-
sioning devices results in premature screen failure. ers of screen cloth of different mesh size presents
Excessive solids accumulation in conjunction with
poor solids conveyance, causes increased wear on
Screen Failure Causes
A. Within one hour
1. Heavy solids loading
2. Vibrators operating improperly
3. Coarse formations on fine screen cloths
B. Within several hours
1. Missing tension bolts or Ramp-loks®
2. Vibrators operating improperly
3. Damaged shaker bed
4. Missing channel rubbers
C. Within one day
1. Damaged shaker bed
2. Inoperable vibrator
3. Extremely heavy mud weights
4. Misalignment of screens
(with three-dimensional screens)
D. Within several days
1. Hematite used as a weighting agent
2. Worn channel rubbers
3. Worn side or cross supports
4. Bent drawbars
dimensional screen, if the screen is not in alignment.
late and wear screens in that area.
Another possible cause of improper solids con-
motion vibrators running in the same direction,
which causes an improper vibration pattern. This
results in massive amounts of solids to accumu-
late on the first screens, causing them to wear
quickly. This can easily be remedied by reversing
the electric wiring to the motors. The vibrators
of the shakers should be tested before spudding
the well. Also, be certain that both vibrators are
operating. If not, replace the inoperable vibrator.
API Recommended Practice for
Designations of Shale Shaker Screens
Shale shaker screens made of two or three lay-
openings that historically have not been easy to
characterize. A technique to describe these openings