It is now commonly understood that effective removal of drilled solids from drilling fluid is fundamental to jobsite performance. In fact, it is rare to see drilling rigs operating without some form of solids control system in place. This has been driven by the growing number of benefits that a well-designed solids control system provides. Including but not limited to,
- Increased rate of penetration,
- Reduction in mud costs,
- Reduction in disposal costs, and
- Increased mud pump and bit life.
By and large, increased drilled solids removal equates to lower drilling costs and lower long-term maintenance costs. However, in order to achieve those benefits, today’s drilling fluid reclamation systems must first rely on a quality vibratory shaker.
Otherwise known as shale shakers, shakers are the first line of defense for a properly designed solids control system. Shakers have been used on conventional drilling rigs since the 1940s and are a significant part of the drilling process. Choosing the right shaker for your operational needs is crucial in maximizing solids control operations. However, making the right choice can be a confusing, and in many cases, frustrating experience. Key variables that should be considered include:
- Deck inclination (i.e. positive or negative screen slopes),
- Vibration type (i.e. linear motion, balanced elliptical motion, progressive linear motion, or orbital / circular motion),
- Adjustable or responsive G-force technology,
- Screen type and surface area (i.e. profile wire vs. fine mesh wire, single mesh vs. multi-layered mesh, flat panel vs. corrugated wave, and wedge fastened, hook strip or pneumatic),
- Abrasion resistance / durability, and
- Upfront capital cost vs. total cost of ownership.
When drilling fluid, laden with drilled solids, flows across the shaker screen, residence time plays an important factor in liquid/solid separation. Shaker inclination influences the time the fluid stays on the screen. Further, when a positive deck angle is selected, pooling of the drilling fluid is allowed to occur on the shaker screens. This allows for a higher head pressure across the screen surface and can improve the hydraulic capacity of the shaker. Typical shakers feature leveling jacks that allow the deck to be adjusted to a declined (downward or negative), horizontal (flat) or inclined (upward or positive) position.
New innovations in shaker design offer single point jacking systems that can operate via electric motor, gear-driven assembly or pneumatic operation. These new actuation systems allow the operator to adjust the deck inclination with minimal effort during operation (a.k.a. AWD, “adjustable while drilling”) quickly and efficiently.
Early shaker designs featured a single motor mounted either away from the center of gravity or at the center of gravity section of the shaker basket. These two positions produce orbital / circular motion. Such designs produced poor results as they were limited to coarse screens and provided for limited solids conveyance.
In the late 1980s, the introduction of linear motion technology allowed operators to utilize a wide range of screens to effectively process material across the entire screening surface. Consequently, linear motion presents conveyance challenges with a positive deck inclination and when the drilling solids include clay. In addition, it has been found that linear motion imparts a relatively “violent” response at the top and bottom of its motion range. Thus, in the 1990s, balanced elliptical motion was introduced.
Balanced elliptical motion (and its variant, progressive linear motion) reduced the “violent” response at the top and bottom the shaker’s movement. This ultimately proved effective in dealing with clays and provided evidence that screen life could be extended. Consequently, balanced elliptical motion came at a financial cost and a hydraulic throughput cost. Such vibrator motors are more expensive to deploy and presented slightly less G-force at the screen surface, therefore reducing the overall hydraulic capacity of the shaker.
Traditional shaker manufacturers offer either linear motion or balanced elliptical motion configurations. However, in recent years, new innovations in vibrator motor design have introduced shakers to the market that feature dual-motion options. This technology allows the operator to adjust the shaker motion during operation without having to shut down the system.
Adjustable or Responsive G-force
In addition to choosing the right shaker motion for your operations, the available G-force is equally important. Shaker motors come in a variety of horsepower configurations that generally range in G-force from 3 to 8 Gs. The higher the G-force, the more effective liquid/solid separation occurs. However, it is important to remember that with higher G-force, the shorter the screen life.
Traditional shakers on the market require the operator to shut down the shaker and manually adjust the concentric weights inside the motor to either increase or decrease the applied G-force. This procedure is time consuming. New innovations in shaker control systems adopt a variable frequency drive (VFD) that allows the operator to easily adjust the imparted G-force without having to shut down the shaker.
Screen Type and Surface Area
Currently, there are several different screen designs on the market and most of today’s manufacturers focus on the frame structure and shaker fastening applications. Traditional screens are constructed using a rigid steel frame and perforated plate; in which layers of woven wire cloth are bonded with powder-coating. New technology has advanced shaker screen construction using composite materials, therefore improving durability and performance.
Composite screens can provide higher surface tension. As such, the wire mesh experiences less fatigue wear. This translates to a more precise cut point and a longer service life.
One of the most important variables is total screen surface area deployed. Maximizing surface area can be achieved by increasing the number of screen decks and/or providing corrugated wave screens. Corrugated wave screens feature up to 50% more screen surface area. This maximizes liquid/solid separation per square foot of screen deployed.
Even when it comes to securing screens, there are a variety of available configurations, each with their own advantages and disadvantages. Wedge fastened screens provide an easy and low-cost option but tend to be more time consuming. Conversely, hook strip screens provide a less time-consuming alternative, but present a much higher price point.
Choosing the right shaker is a long-term investment. Since shakers are constantly exposed to highly abrasive solids and constant G-force thrust, it is important to select a shaker that is rugged and durable. The thickness of the steel used, use of full seam-welded construction vs. huck-bolt construction, and the use of powder-coat or wet paint are all factors worthy of consideration when selecting a shaker.
Today’s shakers start at a cost ranging from $15,000 up to $40,000 depending on size, number of screen panels and available options. The average monthly consumables can range from $500 up to $2,500 a month when operating on a full-time basis. The benefits of deploying the right shaker yields significant jobsite operational cost savings. Recovery of lost drilling fluid reduces the cost associated with make-up water. Additionally, the right shaker and screen selection can yield a drier solid waste cutting, which reduces the material disposal costs. With the proper selection, a properly design shaker system can pay for itself within 12 to 18 months.
When choosing the right shaker for your operational needs, it is important to fully evaluate all features offered to maximize drilling fluid recovery and minimize waste disposal. Making the wrong choice will impact rig site performance and result in higher operational costs.