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GENERAL COMMENTS ON GAS CUTTING

Solids-control equipment can be severely affected by gas in the drilling
mud. This condition is misinterpreted and misunderstood in most
field applications. The primary problems caused by gas cutting in solids
control are blinding of the shaker screens and degradation of pump
output to hydrocyclones and centrifuges. Gas cutting always occurs
during drilling of a gas-bearing formation.
If there is enough gas to displace drilling fluid to the surface (and
increase pit volume), bottom-hole pressure is reduced. This occurs when
the pressure exerted by the drilling fluid is less than the formation pressure and there is some significant permeability. This condition requires surface control, gas busters or separators, and a degasser.
If there is no pit volume increase but the drilling fluid is gas cut and
the flowline mud density reduced, bottom-hole pressure is not significantly reduced and this condition in general calls for only a degasser. (see inclined letter )

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SETTLING PITS

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.

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NON–OILFIELD DRILLING USES OF SHALE SHAKERS

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.

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Three-Dimensional Screening Surfaces

Three-dimensional screen panels were introduced in the mid-1990s. These typically offer between 75 and 125% more screening area than flat-panel repairable plate screens, while retaining the ability to be repaired. Compared with nonrepairable hook-strip screens, most threedimensional screen panels offer up to 45% more screening area. This type of screen panel adds a third dimension to the previous, twodimensional screens.
The screen surface is rippled and supported by a rigid frame. Most three-dimensional screen panels resemble the metal used in a corrugated tin roof. Construction consists of a screen cloth that is in fact corrugated, pretensioned, and bonded to a rigid frame.

Like bonded flat screens, the three-dimensional screen panel needs only to be held firmly in place with a hook strip or other means to prevent separation between the shaker bed and the screen panel during vibration.
Three-dimensional screen panels can be used to support any type or style of wire cloth and with any type of motion. They improve any shaker performance over comparable flat-screen surfaces under most drilling conditions. Three-dimensional screens may not improve shaker performance when drilling gumbo or large, pliable, sticky cuttings.
Three-dimensional screen panels allow solids to be conveyed down into the trough sections of the screen panel. When submerged in a liquid pool, this preferential solids distribution allows for higher fluid throughput than is possible with flat-screen panels by keeping the peaked areas clear of solids. A three-dimensional screen panel improves distribution of fluid and solids across the screen panel.