Drilling fluid enters the removal-tank section after it passes through the
main shale shaker. Immediately below the main shaker is the first pit,
called a settling pit or sand trap. Fluid passing through the shaker screen
flows directly into this small compartment. The fluid in this compartment
is not agitated. This allows solids to settle. The fluid overflows from
the sand trap into the next compartment, which should be the degasser
suction pit. The sand trap is the only compartment not agitated in the
mud tank system.
Trenchless drilling is one of the fastest growing areas for shale shaker use other than in drilling oil and gas wells. Many of these shakers are used in conjunction with hydrocyclones, creating a mud cleaner.
1. Microtunneling
Microtunneling has become very popular in Europe and is being used more and more in the United States. Microtunneling is horizontal boring of a large-diameter hole (from 27 inches up to 10 feet) while
simultaneously laying pipe. This is typically done in cities for laying or replacing water and sewer pipe under buildings and heavily traveled roads.
Shale shakers remove solids by processing solids-laden drilling fluid over
the surface of a vibrating shaker screen. Particles smaller than the shaker screen openings pass through the screen along with the liquid phase of the drilling fluid.
Larger particles are separated into the shaker overflow for discard.
The shaker screen acts as a ‘go no-go’ gauge. That is, particles larger than
the screen openings remain on the screen and are discarded. Particles
finer than the screen openings go through the screen with the drilling
fluid. The criterion for early shale shaker screens was a long screen
life. This demand for screen life was consistent with the shaker designs
and solids-removal philosophies of the time period. Early shale shakers
could remove only large solids from the drilling fluid. The sand trap,
reserve and settling pits, and downstream hydrocyclones (if utilized)
removed the bulk of drilled solids. Today’s shale shakers are capable
of utilizing finer screens that remove more solids. Desirable characteristics
for a shaker screen are:
1. Economical drilled-solids removal
2. Large liquid flow rate capacity
3. Plugging and blinding resistance
4. Acceptable service life
5. Easy identification
For any particular shale shaker, the size and shape of the shaker screen openings have a great effect on solids removal. This means that the performance of any shaker is largely controlled by the screen cloth used.
The first four items in the preceding list are largely controlled by
choice of screen cloth and by the screen panel technology. Large gains
in shale shaker performance are a direct result of improved screen
cloth and panel fabrication. shaker Screens used on shale shakers have evolved into complex opening patterns.
Every solids-removal system should have enough shale shakers to process 100% of the drilling-fluid circulating rate. In all cases, consult the owner’s manual for correct installation, operation, and maintenance 154 Drilling Fluids Processing Handbook procedures. If an owner’s manual is not available, the following general guidelines may be helpful in observing proper procedures.
