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.
Hook-strip shaker screens (named for the method of hooked edging that
provides the tension along the screen) are also available. Because of the
superior life characteristics of panel mount units, Hook-strip shaker screen has been relegated to a minor role on linear motion machines. They are used
extensively on circular and unbalanced elliptical motion machines.
Proper tensioning (and frequent retensioning) of all types of screens is
good screen management and adds significantly to screen life. Individual
manufacturer’s operation manuals should be consulted to obtain the
proper installation methods and torque requirements, where applicable,
for specific screens/panels.
Several types of bonded screens are available. The repairable perforated
plate screen has one or more layers of fine mesh cloth bonded to a sheet
of metal or plastic with punched, patterned holes. Perforated plate
designs are available in various opening sizes and patterns. Additional
designs include a special application in which backing and fine-screen
materials are bonded together, eliminating the need for perforated
plates. Flat-surfaced pretensioned screen panels are becoming more even
tensioned, easy to install, and capable of even distribution of liquids and
solids across the screen deck.
The materials used to weave the cloth screens are quite varied. Shale shaker screens are made from metal wires, plastic wires, and molded plastic cloths.
Coarse screen and API fine shaker screen
Metals shaker screen
Alloys that are most wearable and resistant to corrosion are nickel/chrome steels; 304, 304L, 316, and 316L. These alloy wires are available in sizes down to 20 microns. The finest wire available is 304L, which is available to 16 microns. Other materials, including phosphor bronze, brass, copper, Monel, nickel, aluminum alloys, plain steel, and plated steel, are also available. Within the drilling industry, 304 stainless cloth is the most common.
Plastics shaker screen
Two types of synthetic screens are available: woven synthetic polymer and molded a one-piece cloth called a platform. Conventional looms can be used to weave synthetic polymer screens. Polymers, such as polyesters, polypropylene, and nylon, are drawn into strings having diameters comparable to those of wire gauges and woven into screen cloth. Synthetic shaker screens exhibit substantial stretch when mounted and used on shale shakers. Because of this, plastic screen openings are not as precise, although this variability is not nearly as great as in layered metal steel screens.
Polyurethane shaker screen
One-piece injection-molded synthetic clothes are typically made from urethane compounds. These synthetic cloths have limited chemical and heat resistance but display excellent abrasion resistance. The designs range from simply supported molded parts having very few open areas to complex structures with up to 55% open area. Molded clothes are very popular in the mining industry, where abrasion resistance is important. These screens make a coarser separation than screens used in the oilfield. The development of molded cloth screens capable of making a fine separation that has heat and chemical resistance necessary for oilfield application is underway. Cloth selection for shale shaker screens involves compromises among separation, throughput, and screen life.
Screen blinding occurs when grains of solids being screened find a hole in the screen just large enough to get stuck in. This often occurs during the drilling of fine sands in the Gulf of Mexico. The following sequence is often observed during screen blinding:
When a new screen is installed, the circulating drilling fluid falls through the screen a short distance.
After anywhere from a few minutes to even several hours, the fluid end point slowly or even quickly travels to the end of the shaker.
Once this occurs, the screens must be changed to eliminate the rapid discharge of drilling mud off the end of the shaker.
After the screens have been washed, fine grains of sand are observed stuck in the screen.
The surface of the screen will feel like fine sandpaper because of the sand particles stuck in the openings.
Most every shaker screen used in the oilfield is blinded to some extent by the time it has worn out. This is the reason that when the same screen size is reinstalled, the fluid falls through the screen closer to the feed.
A common solution to screen blinding is to change to a finer or coarser screen than the one being blinded. This tactic is successful if the sand that is being drilled has a narrow size distribution. Another solution is to change to a rectangular screen, although rectangular screens can also blind, with multiple grains of sand. Unfortunately, the process of finding a screen that will not blind is expensive.
In the late seventies the layered screen was introduced to avoid screen blinding. This hook-strip type of screen was mounted on a downhill sloping unbalanced elliptical motion shale shaker vibrating at 3600 rpm. The two fine layers of screening cloth, supported at 4-inch intervals, tended to dislodge fine grains of sand and would blind only about 25% of the screen in severe laboratory tests, leaving 75% of the screen nonblinded.
The nonblinding feature is assumed to be the result of the deceleration of the two screens. The wire diameter is in the range of 0.002 inch and the opening sizes are in the range of 0.004 inch. In the upward thrust of a layered screen, the screens must come to a stop at the upward end of the motion. They would tend to each have an inertia that would prevent them from stopping at exactly the same time.
This would create an opening size slightly larger than the original opening size of the layered screen during the upward part of the thrust. Solids would be expelled from the screen. On the downward thrust of the motion, the two layers remain together until the screen starts deceleration.
At the bottom of the stroke, again the inertial forces could cause the screens to slightly separate, allowing larger solids to pass through the screen. This probably also explains why the separation cut point curve shows poorer separation characteristics for a layered screen than for a single square mesh
screen. Many particles larger and smaller than the median opening size are found in the discard from a layered screen.
Unfortunately, the downhill sloping basket and high frequency limitsthe amount of liquid that can pass through the screen. Furthermore,lost circulation material has a high propensity to get stuck in the screen due to the high-frequency, short-stroke vibration.
These problems have been ameliorated by reducing the vibration to 1800 rpm and flattening the basket slope. In the early 1980s, linear motion was introduced so that solids could march up an incline out of a pool of liquid. This fluid pool provided additional pressure to force fluid through the screen.
Unfortunately, linear motion, combined with marginal support, tore layered screens apart. The only way to obtain satisfactory screen life ona linear motion machine was to support the layered screen in 1-inch squares.
