Most service providers and exploration and production companies understand that effectively removing solids from drilling fluid is fundamental to job site performance and enhanced efficiency. Drilling fluids are a key aspect of the drilling process because they lubricate and cool the drill bit and take drill cuttings from the borehole. Solids control has a wide range of benefits including, but not limited to:
- Increased drilling penetration
- Reduced mud costs
- Decreased disposal costs
- Increased bit life
Essentially, increased solids removal means lower drilling costs for the operator. Shale shakers are the first line of defense in a properly designed solids control system. Shakers have been used on drill rigs since the 1940s and are a significant part of the drilling process. Shale shakers work by removing solids from drilling fluid as the mud passes over the surface of a vibrating screen. The liquid portion of the mud and solids passes through the screen while the larger solids fall off the back end and are discarded. Shakers remain the backbone of any solids control system but, as time has progressed, so have these technologies. More advanced and efficient designs have been developed including screen technology. A screen on a shaker acts as an acceptability gauge. Either a particle is small enough to pass through the screen, or it is not. Most screening surfaces used in current solids control equipment are made of multilayered woven wire screen cloth. Generally, multilayered, mesh screens with tensioned stainless steel wire mesh that meet American Petroleum Institute (API) specifications are the most effective. With today’s innovations, a wider range of screen technologies is available that can optimize solids control systems.
Pre-tensioned screens are available in different sizes to fit individual systems. Operating conditions should determine screen selection. Since screen mesh count and screen ratings can significantly impact shaker performance, choosing the correct screen is critical. Each screen directly influences the ability of the shaker to achieve solid/liquid separation and consistent conveyance. As a general rule, coarser screens are placed on the rear and lower decks, while finer mesh screens are placed near the output. If using a dual deck shaker, finer screens are usually located on the top deck and more coarse screens on the bottom. Operators should remember that finer screens wear more quickly, especially when subjected to high volumes of solids, such as when top-hole drilling is occurring. Experience will also help guide screen selection regarding flow rate and solids type to maximize solids removal and discharge dryness.
Materials of Construction & Wire Diameter
When selecting a screen, end users should pay special attention to the screen design and the size of the opening. Most manufacturers focus on the frame structure and shaker fastening applications. However, focusing on a multilayered, wire cloth formula and wire diameter is critical. One manufacturer’s bottom layer of screens is comprised of thicker, market-grade wire. This yields a stronger base, which allows the other layers to maximize performance during the most severe conditions. These screens are made of materials including 304 stainless steel, woven wire cloth, 12-gauge perforated punch plate and a one-inch steel tubing frame. These materials help increase the shaker screen’s durability. One manufacturer developed a line of polyester-powder-coated screens. This special powder coating is based on a polyester resin for improved mechanical bonding and enhance mechanical properties when compared to polyester alone. This careful blend of additives allows for a higher level of cross-linking of the resin binder, which ultimately produces a harder and more durable coating.
The API screen designation is the customary standard for the identification of screen panels in the industry. Before the API RP 13C standard, a huge disparity existed in screen designations, which caused confusion for end users. Specific to screens, the API designation is the micron opening size and the conductance, which is measured by the ease of flow for liquids through the screen. Larger volumes represent a higher volume of handling. Screen manufacturers in compliance with API provide screen labeling that includes the following information:
- API designation
- Conductance in kilodarcies per millimeter
- D100 particle size value
- Non-blanked open area in square feet
Some manufacturers provide screens that are all API rated and tested by third-party agencies to meet API RP 13C requirements. Screens may also be subjected to other tests including chemical immersion testing in fluids such as diesel, alpha-olefin, calcium chloride, caustic soda and kerosene. In all cases, one manufacturer’s polyester, powder-coated screens demonstrated environmental exposure resistance when compared to other screens.
Protect the Investment
Operators must consider how to protect their investment beyond purchasing durable screens. Proper maintenance will affect all screens’ quality. On the job site, screens should be stored in their boxes and stacked flat (or in accordance with the manufacturer’s recommendations). Mishandling panels, especially during storage and installation, may cause premature screen failure. Operators should also make sure that screens are always properly mounted, check for proper tensioning and replace worn deck and crown (channel) rubbers as soon as possible. Personnel should never walk on screens when working on shakers. They should also avoid dropping tools on screens. After service each day, screens should be washed down, especially if drilling is occurring in sticky solids such as clay. Periodically, screens should be thoroughly inspected for tears and holes. If unresolved, these issues will result in a major mud weight problem and may cause a heavy buildup of solids being returned to the active mud tank. Monitoring for extremely high mud weights will also help extend screen life. All personnel must be aware of the proper operation, installation, storage and maintenance of shaker screens.