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Section 300 SOLIDS CONTROL HANDBOOK Schlumberger Dowell

Shale Shakers

January 1998 Page 1 of 36

Shale Shakers 1 Introduction .........................................................................................................................3

2 Principle of Operation.........................................................................................................4 2.1 Vibration Patterns ..........................................................................................................4 2.1.1 Circular Motion .....................................................................................................5 2.1.1.1 Solids Conveyance and Fluid Throughput................................................5 2.1.1.2 Recommended Applications ....................................................................5 2.1.2 Unbalanced Elliptical Motion ................................................................................5 2.1.2.1 Solids Conveyance and Fluid Throughput................................................6 2.1.2.2 Recommended Applications ....................................................................6 2.1.3 Linear Motion .......................................................................................................6 2.1.3.1 Solids Conveyance and Liquid Throughput..............................................7 2.1.3.2 Recommended Applications ....................................................................7 2.1.4 Balanced Elliptical Motion ....................................................................................8 2.1.5 Vibration Dynamics ..............................................................................................9 2.1.5.1 Acceleration.............................................................................................9 2.1.5.2 Frequency (RPM), Stroke Length .......................................................... 11 2.1.6 Deck Angle ........................................................................................................ 12

3 Screen Fastening and Support ........................................................................................ 12 3.1 Hookstrip Screen Panels ............................................................................................. 13 3.2 Rigid Frame (Pretensioned) Screen Panels ................................................................. 15

4 Single Deck Shakers......................................................................................................... 17

5 Cascading Shaker Systems.............................................................................................. 21 5.1 Unitized Cascading Systems ....................................................................................... 22

6 Integral Tandem Deck Shakers ........................................................................................ 23

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7 Shaker Manifolds ..............................................................................................................27

8 Operating Guidelines........................................................................................................30 8.1 Optimizing Screen Life.................................................................................................30 8.2 Screen Selection .........................................................................................................30 8.3 Cuttings Dryness .........................................................................................................30 8.4 Sticky Solids (Gumbo) .................................................................................................32 8.5 Polymer Muds..............................................................................................................33 8.6 Blinding, Plugging ........................................................................................................33 8.7 Lost Circulation Material ..............................................................................................33

9 Estimating Number of Shakers Required ........................................................................34

10 Summary..........................................................................................................................35 FIGURES Fig. 1. Shale shaker components............................................................................................4 Fig. 2. Circular motion. ............................................................................................................5 Fig. 3. Unbalanced elliptical motion.........................................................................................6 Fig. 4. Linear motion. ..............................................................................................................7 Fig. 5. Balanced elliptical motion.............................................................................................8 Fig. 6. Conveyance velocity. ...................................................................................................9 Fig. 7. Adjustable vibrator counterweights.............................................................................10 Fig. 8. Shaker throughput versus vibrator frequency. ............................................................11 Fig. 9. Solids bed buildup......................................................................................................12 Fig. 10. Typical hookstrip screen...........................................................................................13 Fig. 11. Hookstrip screen tensioners. ....................................................................................14 Fig. 12. Shaker fluid endpoints..............................................................................................15 Fig. 13. Rigid screen panel with perforated plate...................................................................16 Fig. 14. Rigid screen panel....................................................................................................17 Fig. 15. Derrick flo-line cleaner plus. .....................................................................................18 Fig. 16. Fluid systems model 500..........................................................................................18 Fig. 17. Swaco ALS. .............................................................................................................19 Fig. 18. Sweco LF-3 oil-mizer................................................................................................19 Fig. 19. Sweco LM-3. ............................................................................................................20 Fig. 20. Triton NNF. ..............................................................................................................20 Fig. 21. Cascading shaker system. .......................................................................................21 Fig. 22. Brandt ATL-CS.........................................................................................................23 Fig. 23. Brandt ATL 1000 ......................................................................................................24 Fig. 24. Derrick cascade system. ..........................................................................................25 Fig. 25. Thule VSM 100 ........................................................................................................26 Fig. 26. Poor manifold design................................................................................................27 Fig. 27. Better manifold design..............................................................................................28

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Fig. 28. Best conventional manifold design. .......................................................................... 28 Fig. 29. Circular manifold design........................................................................................... 29 Fig. 30. Overhead manifold design........................................................................................ 29 TABLES Table 1 Shakers Required..................................................................................................... 34

1 Introduction The shale shaker can be regarded as the “first line of defense” in the solids removal system. It has proven to be a simple and reliable method of removing large amounts of coarse, drilled cuttings from the circulating system. The shale shaker’s performance can be easily observed; all aspects of its operation are visible. Shale shakers provide the advantage of not degrading soft or friable cuttings. When well-operated and maintained, shale shakers can produce a relatively dry cuttings discharge. In unweighted muds, the shale shaker’s main role is to reduce the solids loading to the downstream hydrocyclones and centrifuges to improve their efficiency. In muds containing solid weighting agents such as barite, the shale shaker is the primary solids removal device. It is usually relied upon to remove all drilled cuttings coarser than the weighting material. Downstream equipment will often remove too much valuable weighting material. Enough shakers should be installed to process the entire circulating rate with the goal of removing as many drilled cuttings as economically feasible. Given the importance of the shale shaker, the most efficient shakers and screens should be selected to achieve optimum economic performance of the solids control system. Shaker performance is a function of: ·

Vibration pattern

·

Vibration dynamics

·

Deck size and configuration

·

Shaker screen characteristics

·

Mud rheology (plastic viscosity)

·

Solids loading rate (penetration rate, hole diameter)

The impact of each is discussed in detail in this chapter. Guidelines for shaker and screen selection are also provided.

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2 Principle of Operation Simply stated, a shale shaker works by channeling mud and solids onto vibrating screens. The mud and fine solids pass through the screens and return to the active system. Solids coarser than the screen openings are conveyed off the screen by the vibratory motion of the shaker. The shaker is the only solids removal device that makes a separation based on physical particle size. Hydrocyclones and centrifuges separate solids based on differences in their relative mass. The screens are vibrated by rotating eccentrically-weighted shafts attached to the basket. The major components of a typical shale shaker are illustrated in Fig. 1.

Fig. 1. Shale shaker components. Note: These components are common to most shale shakers.

2.1 Vibration Patterns Shale shakers are classified in part by the vibration pattern made by the shaker basket location over a vibration cycle (e.g., “linear motion” shakers). The pattern will depend on the placement and orientation of the vibrators. Four basic vibration patterns are possible: circular, unbalanced elliptical, linear, and balanced elliptical motion.

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2.1.1 Circular Motion As the name implies, the shaker basket moves in a uniform circular motion when viewed from the side (Fig. 2.). This is a “balanced” vibration pattern because all regions of the shaker basket move in phase with the identical pattern. In order to achieve “balanced” circular motion, a vibrator must be located on each side of the shaker basket at its center of gravity (CG) with the axis of rotation perpendicular to the side of the basket. The Brandt Tandem is a common example of a circular motion shale shaker.

Fig. 2. Circular motion. Note: All areas of the basket rotate in a circular motion. 2.1.1.1 Solids Conveyance and Fluid Throughput Circular motion shakers will not efficiently convey solids uphill. Therefore, most shakers of this type are designed with horizontal configurations. Fluid throughput is limited by the deck angle, but augmented slightly by the higher G’s normally used (see Vibration Dynamics section). The “soft” acceleration pattern does not tend to drive soft, sticky solids, such as gumbo, into the screens. 2.1.1.2 Recommended Applications ·

gumbo, or soft, sticky solids conditions

·

scalping shakers for coarse solids removal

2.1.2 Unbalanced Elliptical Motion The difference between circular motion and unbalanced elliptical motion is a matter of vibrator placement. To achieve unbalanced elliptical motion, the vibrators are typically located above the shaker basket. Because the vibrator counterweights no longer rotate about the shaker’s center of gravity, torque is applied on the shaker basket. This causes a rocking motion which generates different vibration patterns to occur along the length of the basket,

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hence the term “unbalanced.” Refer to Appendix F, Equipment Specifications, for a list of shakers having unbalanced elliptical motion. Fig. 3. illustrates how the vibration pattern may change along the length of the basket. At the feed end of the shaker, an elliptical vibration pattern is created; the angle of vibration is pointed toward the discharge end. In this region, forward solids conveyance is good. However, at the discharge end of the shaker, angle of the elliptical pattern is pointed back towards the feed end. This will cause the solids to convey backwards unless the deck is pitched downhill at a sufficient angle to overcome the uphill acceleration imparted on the solids by the shaker motion.

Fig. 3. Unbalanced elliptical motion. Note: The vibration pattern changes along the length of the basket. 2.1.2.1 Solids Conveyance and Fluid Throughput The downhill deck orientation restricts the unbalanced elliptical motion shaker’s ability to process fluid; mud losses can be a concern. However, the deck orientation is beneficial for removing sticky solids such as gumbo. 2.1.2.2 Recommended Applications ·

gumbo, or soft, sticky solids conditions

·

scalping shakers for coarse solids removal

2.1.3 Linear Motion Linear motion is achieved by using two counter-rotating vibrators which, because of their positioning and vibration dynamics, will naturally operate in phase. They are located so that a line drawn from the shaker’s center of gravity bisects at 90° a line drawn between the two axes of rotation (Fig. 4.).

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Fig. 4. Linear motion. Note: All areas move in a synchronous linear motion. Because the counterweights rotate in opposite directions, the net force on the shaker basket is zero except along a line passing through the shaker’s center of gravity. The resultant shaker motion is therefore “linear.” The angle of this line of motion is usually at 45-50° relative to the shaker deck to achieve maximum solids conveyance. Because acceleration is applied through the shaker CG, the basket is dynamically balanced; the same pattern of motion will exist at all points along the shaker. 2.1.3.1 Solids Conveyance and Liquid Throughput Linear motion shakers have become the shaker of choice for most applications because of their superior solids conveyance and fluid-handling capacity. Solids can be strongly conveyed uphill by linear motion. The uphill deck configuration allows a pool of liquid to form at the shaker's feed end to provide additional head and high fluid throughput capability. This allows the use of fine screens to improve separation performance. The Derrick Flo-Line Cleaner is one example of a linear motion shale shaker. One drawback to linear motion shakers is their relatively poor performance in processing gumbo. The short vibration stroke length when combined with long, basket lengths, uphill deck angles and strong acceleration forces tends to make the soft gumbo “patties” adhere to the screen cloth. Some success has been reported by using linear motion shakers with short deck lengths and horizontal or downhill deck angles. 2.1.3.2 Recommended Applications ·

All applications where fine screening is required.

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2.1.4 Balanced Elliptical Motion Amoco's analytical shaker dynamics model has predicted that this is the optimum vibration pattern for maximum solids conveyance. Unlike “unbalanced” elliptical motion, all points on the shaker basket move in phase with the identical elliptical pattern. The model predicts that a “thin” ellipse will provide solids conveyance superior even to linear motion. Because elliptical motion provides a “softer” acceleration pattern than linear motion, it is likely that screen life may also be improved. Amoco Production Research has recently tested a simple and commerciallyviable method to achieve balanced elliptical motion. The vibrators are located as shown in Fig. 5. The vertical orientation of the vibrators dictates the shape of the ellipse. The more the vibrators are tilted out from the shaker basket, the more circular the vibration pattern.

Fig. 5. Balanced elliptical motion. Note: This motion is the most efficient in conveying solids. Full-scale experiments have verified analytical model predictions of improved solids conveyance with a thin ellipse. In Fig. 6, the numbers in parentheses are the ratios of major axis length to minor axis length of the vibration patterns. By adjusting the shape of the ellipse, solids conveyance velocity can be adjusted without changing deck angle or acceleration normal to the screen. This feature has potential for optimizing cuttings conveyance with respect to oil retention on cuttings.

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Fig. 6. Conveyance velocity. Note: The shape of the ellipse controls conveyance velocity. A thin ellipse conveys solids faster than linear motion.

2.1.5 Vibration Dynamics 2.1.5.1 Acceleration During the vibration cycle, the shaker basket undergoes acceleration which changes in both magnitude and direction. As discussed previously, the placement of the vibrators determines the vibration pattern and therefore the net acceleration direction during the vibration cycle. The mass of the counterweights and the frequency of the vibration determine the magnitude of the acceleration. The vertical component of acceleration has the most effect on shaker liquid throughput. We relate the vertical components of acceleration and stroke length to frequency by the following equation: G's =

stroke (in.) x RPM2 70,400

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where the stroke length is the total vertical distance traveled by the shaker basket and the G-force is measured from midpoint to peak. An acceleration of one “G” is the standard acceleration due to gravity (386 2 in./sec ). Most shakers operate at accelerations within the range of 2.5-5.0 G’s, depending upon the vibration pattern. Field experience has shown this range offers the best compromise between throughput capacity and screen life. Many manufacturers report the acceleration of linear motion shakers along the line of motion. This yields a larger number and looks good on the specification sheet. However, unless the angle of vibration is also specified, it reveals little about the performance of the shaker. The “G's” for shale shakers listed in the appendix are calculated for the direction normal to the screen surface. Some shakers have adjustable counterweights to vary acceleration (Fig. 7). Although flow capacity and cuttings dryness improves with increased acceleration, screen life is negatively affected. By reducing the “G’s” when extra flow capacity is available, screen life may be improved.

Fig. 7. Adjustable vibrator counterweights. Note: Other designs are used, this is the most simple.

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2.1.5.2 Frequency (RPM), Stroke Length The vibrator frequency of most shale shakers is not normally adjustable. The vibrators typically rotate at a nominal rpm of 1200 or 1800 at 60 Hz. Stroke length varies inversely with rpm. A higher rpm will result in a shorter stroke length at the same acceleration. The effect of vibrator frequency and stroke length on shaker processing rate has been evaluated in the laboratory. The results of these tests show improved shaker flow capacity in the presence of solids with decreased rpm (or conversely, increased stroke length) at the same G level. (Fig. 8). Therefore, the term “high speed” should not be used to mean “high performance” since the opposite relationship is often more correct.

Fig. 8. Shaker throughput versus vibrator frequency. Note: Shaker throughput improves as frequency decreases. The main disadvantage to lower frequency shale shakers is that the mud tends to “bounce” much higher off the screens and cover the area around the shakers with a fine coating of mud. More frequent housekeeping is required to maintain a safe environment around the shakers. Longer stroke lengths also tend to reduce screen life.

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2.1.6 Deck Angle Because linear motion shakers will convey uphill, most provide an easilyadjustable deck angle feature to optimize fluid throughput capacity and cuttings conveyance velocity. Uphill deck angles also provide protection against overflow due to surges at the flow line. At deck angles greater than 3°, solids grinding in the pool region can be a problem. Although fluid throughput increases with uphill deck angle, cuttings conveyance decreases. Solids conveyance within the pool region is slower than out of the pool due to viscous drag forces and the differential pressure created across the cuttings load by the hydrostatic head of the fluid. If the deck angle is too high, a stationary mound of solids can build up in the pool even though conveyance is observed at the discharge end (Fig. 9). The vibrating action of the screen and extended residence time will tend to grind soft or friable cuttings before they have the opportunity to be conveyed out of the pool. This condition should be avoided since the generation of fines in the mud is definitely not desired. To check for this problem, observe the feed end of the shaker at a connection immediately after circulation is stopped. There should not be a disproportionate amount of solids accumulated at the feed end. The problem can be rectified by lowering the deck angle until the solids mound is eliminated.

Fig. 9. Solids bed buildup. Note: This may occur when the shaker deck is tilted up to high.

3 Screen Fastening and Support The type of screen panel dictates the type and amount of support and fastening system necessary. The screen fastening and support structure provide the following functions:

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1.

Prevent leakage past the screens

2.

Expedite screen replacement

3.

Provide even tension on screens to extend screen life


The two types of screen panels are commonly labeled as “pretensioned” and “nonpretensioned” panels. However, these terms do not exactly describe their construction since many nonpretensioned panels are, indeed, pretensioned. The terms “rigid frame” and “hookstrip” more correctly differentiate the two main panel types.

3.1 Hookstrip Screen Panels This is the most common type of panel, consisting of one to three layers of screen cloth. The cloth is frequently bonded to a thin perforated-metal grid plate or a plastic grid. Fig. 10 shows the construction of a typical hookstrip screen. The screen panel is tensioned on the shaker deck by an interlocked hookstrip and drawbar arrangement located on both sides of the shaker (Fig. 11). Three or more tensioning bolts are used to pull each drawbar down and towards the side of the basket. This seats the screen on the shaker deck and distributes even tension along the hookstrip.

Fig. 10. Typical hookstrip screen. Note: The backing grid, though not necessary, provides support and improves screen life.

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Fig. 11. Hookstrip screen tensioners. Note: This is the most common type of fastening system for hookstrip screens. These panels are not rigid; the shaker deck must be crowned to maintain screen-to-deck contact throughout the vibration cycle. Support ribs in the shaker deck are designed to ensure even support of the screen across the width of the basket. Full contact with all support stringers is critical, especially with metal-backed panels. The panels will suffer premature fatigue failure if flexing is allowed to occur. Because screen tension is extremely important to ensure good screen life, the tension should be checked frequently on nonpretensioned hookstrip-style screens. Spring-loaded tensioning bolts are recommended to aid in preventing a complete loss of tension and premature failure as the screens stretch and “seat” onto the deck. Tensioning springs are not required for hookstrip panels with metal backing plates since these panels will not normally stretch. The crowned deck can cause uneven fluid coverage (Fig. 12). The mud may extend further out along the sides of the shaker than at the center where maximum deck height occurs. This reduces the effective screening area of the shaker, especially at low deck angles. It can lead to whole mud losses at the discharge and contribute to unacceptably wet cuttings even though the fluid endpoint along the centerline of the shaker may be well back from the discharge. The problem can be mitigated by increasing the deck angle and selecting high efficiency screens to reduce fluid coverage area. Screen replacement time is usually much longer than with rigid frame panels. However, Derrick has developed a new tension bolt design which has improved screen changing on their Flo-Line Cleaner; the tensioning nut and spring have been replaced by an integral nut and spring assembly which requires a half-turn to fully operate.

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Fig. 12. Shaker fluid endpoints. Note: Crowned decks will cause uneven fluid coverage especially at low deck angles.

3.2 Rigid Frame (Pretensioned) Screen Panels In rigid frame screen panel construction, the screen cloth is tensioned and bonded to an integral steel frame; no additional tensioning is required. Because rigid frame screens are flat, uneven fluid coverage on the shaker is not a problem. All other factors being equal, discharged cuttings dryness is reported to be superior to shakers with hookstrip screen designs. Since no tensioning is required during installation, the fastening system can be designed for fast panel replacement. For example, each panel on the Fluid Systems Model 500 is held in place by two wedges (one on each side). A tap on the wedge locks the panel in place. The Thule VSM100 has a

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pneumatically-actuated system. Sweco's LF-3 Oil-Mizer and Brandt's ATL1000 also have quick-release fastening systems. The two most common types of pretensioned panels are shown in Fig. 13 and Fig. 14. 1.

The screen cloth is tensioned and glued directly to the steel frame. Additional glue lines may be included between the frame members to provide additional support. The bonding pattern divides the panel into 3to 4-in. wide strips oriented parallel to the flow. This design is used in the Fluid Systems Model 500. This panel design maximizes usable screening area. However, the large unsupported area normally limits cloth selection to the heavier grades with lower flow capacity. The panel is not normally considered repairable.

2.

Alternatively, the screen cloth may be bonded to a perforated metal backing plate similar to a hookstrip screen. The metal backing plate is then bonded to the support frame to create a rigid panel. The Brandt ATL-1000 and the Thule VSM-100 use this type of panel. Usable screen area is reduced by the perforated plated design, but this is offset by the option of using higher conductance screen cloth, repairability, and better screen life under high solids loading conditions.

Fig. 13. Rigid screen panel with perforated plate. Note: The metal grid is bonded to a steel frame.

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Fig. 14. Rigid screen panel. Note: The screen cloth is glued directly to a steel frame.

4 Single Deck Shakers As the name implies, a single deck shale shaker has one discrete screening layer; the mud and solids fed to the shaker are screened once. One or more screen panels may be used to provide a continuous screening surface. Deck profiles of single deck linear motion shakers are usually flat from feed to discharge, but other profiles are used. For example, the panels of the Fluid Systems Model 500 and Swaco ALS are arranged in a stairstep pattern: Each downstream panel is slightly lower than the upstream panel, primarily for ease of panel positioning. Unbalanced elliptical motion shakers, such as the Derrick Standard or Swaco Super Screen, have an increasingly negative (downhill) slope on downstream panels to improve solids conveyance. Single deck shakers provide the advantage of allowing complete access to the screening surface. This simplifies maintenance, panel changes, screen inspection and cleaning. The disadvantage of single deck shakers becomes apparent under high solids loading conditions; flow capacity, cuttings dryness and screen life may be greatly reduced. These problems can be circumvented by using a cascading shaker arrangement. (Refer to the following section: Cascading Shaker Systems.) Linear motion single deck shakers are preferred for most applications because of their simplicity, high flow capacity and fine-screening capability. Their popularity has spurred numerous companies to manufacture linear motion shakers. A complete list is provided in Appendix F, Equipment Specifications. Many of the major manufacturers’ shakers have been evaluated in the laboratory at APR. Differences in overall performance were found to be relatively minor. Examples of single deck linear motion shakers that will provide acceptable performance are pictured in Figures 15-20. The

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shakers are listed in alphabetical order, no ranking is implied by the order of their appearance.

Fig. 15. Derrick flo-line cleaner plus.

Fig. 16. Fluid systems model 500.

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Fig. 17. Swaco ALS.

Fig. 18. Sweco LF-3 oil-mizer. CONFIDENTIAL




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Fig. 19. Sweco LM-3.

Fig. 20. Triton NNF.

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5 Cascading Shaker Systems “Cascading” refers to the use of shakers in series (the mud passes sequentially through two shakers) to remove drill cuttings in two stages. The first set of shakers remove or “scalp” the coarsest cuttings from the returned drilling fluid. The mud and fine cuttings are then fed to a second set of shakers with finer screens. This arrangement increases the capacity of the fine screen shakers through reduced solids loading. This arrangement is especially effective when drilling fast, large diameter hole sections or gumbo formations. Fig. 21 illustrates a “2 over 3" cascading shaker arrangement. This arrangement usually provides adequate shale shaker solids removal for drilling most 17-1/2-in. diameter holes. It is important to ensure that valves are provided to isolate each shaker in the system as required for screen maintenance and shaker repair.

Fig. 21. Cascading shaker system. In most instances, unbalanced elliptical or circular motion shakers are the preferred scalping devices. Soft, sticky cuttings such as gumbo are generally handled better by these vibration patterns with a flat or downhill deck angle. However, linear motion shakers have been successfully used as scalpers when the deck angle is steeply pitched downhill (such as a Derrick Standard) or when the deck length is short (such as the Fluid Systems two-panel shaker).

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Because the scalping shakers must be positioned above the fine screen shakers, sufficient height between the flow nipple and the scalping shaker weirs must be available to avoid solids settling in the return line. A good “rule of thumb” is 1 ft of drop per 12 ft of flowline. Also, additional space is obviously necessary to accommodate a cascading system.

5.1 Unitized Cascading Systems A unitized cascading system incorporates two shakers, one stacked over the other, on a single skid. This design reduces many of the plumbing problems and costs normally associated with retrofitting a cascading system on a rig. Also, the unitized system takes up less floor area than a standard cascading system. Because the top and bottom shaker are separate units, each can be designed for its specific function without severely impeding screen panel access or performance. This is an advantage over integral tandem deck shakers. There are two disadvantages to unitized cascading systems: (1) They have high weirs which will limit their application to rigs with sufficient elevation difference between the flow nipple and the upper shaker weir; and (2) the upper shaker may be too high to be worked on easily. A permanent walkway or ladder should be installed to improve access to the upper shaker’s screens. Two systems are currently available: The Brandt ATL-CS (Fig. 22) and the Fluid Systems Model 50-500. The Brandt is a tandem deck, circular motion basket over a linear motion basket. The Fluid Systems version uses a short, two-panel linear motion basket as the scalping shaker over their standard Model 500 shaker.

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Fig. 22. Brandt ATL-CS. Note: This is one example of a “utilized” cascading shaker arrangement.

6 Integral Tandem Deck Shakers These shakers incorporate two distinct screening decks stacked in a single basket. The top deck screen “scalps” off the coarse solids to reduce the solids loading to the lower screens. Tandem deck shakers are available in both circular and linear motion designs. The superior fluid processing and finer screening features of linear motion shakers are preferred. In either case, flow back pans are recommended to improve throughput. Tandem deck shakers offer a compromise between a true cascading system and single deck shakers. If the top scalping deck covers the entire basket width, solids handling capacity is good. However, accessibility to the lower deck screens and the ability to monitor screen wear is limited. Conversely, a

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small scalping deck limits solids loading capacity, but improves accessibility and screen monitoring. Tandem deck shakers are recommended for medium-high solids loading applications or where space or height limitations will not permit the use of a cascading shaker system. The total combined area of both screening surfaces cannot be used to compare the performance of these shakers to single deck shakers. The relative processing capacity of tandem deck shakers will depend upon the size distribution of the solids in the feed, solids generation rate and other factors. Generally, tandem deck shakers will outperform single deck shakers when large diameter hole and high penetration rates are encountered. Examples of linear motion tandem deck shakers are shown in Figures 23-25.

Fig. 23. Brandt ATL 1000.

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Fig. 24. Derrick cascade system.

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Fig. 25. Thule VSM 100.

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Shale Shakers


7 Shaker Manifolds The flowline and manifold system must be designed to provide an even distribution of mud and cuttings to the shakers. The flow line must have sufficient drop to prevent solids from accumulating in the line: A drop of 1 ft per 12 ft of run is a good rule of thumb. Flowline diameter must also be sufficient to handle the maximum anticipated circulation rates. Diameters of 10 or 12 in. are usually sufficient. Manifolding can be a problem when three or more shakers are arranged in parallel. Because the shaker feed is essentially two-phase, liquid being one phase and solids the other phase, equal division of both phases can become difficult to achieve with typical manifold designs (Fig. 26 and Fig. 27). Branch tees should be avoided. The solids will preferentially travel a straight path, resulting in uneven solids loading to the shakers. Dead end tees will distribute the solids more evenly. Examples of recommended manifold designs for multi-shaker installations are provided in Fig. 28, Fig. 29, and Fig. 30. Overhead or circular manifolds will provide better distribution of mud and solids. All shakers should be level with equal weir heights to ensure even flow distribution. A common shaker box (possum belly) is acceptable for scalping shakers. It is not recommended for the fine screen shakers since a large shaker box only serves to collect solids, which can enter the mud tanks if the bypass gate is opened.

Fig. 26. Poor manifold design. Note: Distribution to the shakers may be uneven.

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Fig. 27. Better manifold design. Note: There are less branch tee’s in this design.

Fig. 28. Best conventional manifold design. Note: All branch tee’s are eliminated.

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Fig. 29. Circular manifold design. Note: Useful for odd number of shakers. Flowline lengths are exaggerated.

Fig. 30. Overhead manifold design. Note: Excellent for even distribution of liquids and solids, but more complicated to fabricate.

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8 Operating Guidelines 8.1 Optimizing Screen Life Perforated plate screens usually exhibit longer screen life than other hookstrip screens. They provide the most support and are repairable. 1.

Screen life is inversely proportional to plate opening size. If premature wear is apparent in the pool region, install panels with smaller perforated plate sizes at the feed end of the shaker where loading and wear is greatest.

2.

Reduce deck angles to improve solids conveyance, reduce loading and eliminate solids grinding at the feed end.

3.

If premature backing plate failure is experienced, check that all deck rubbers are in place and in good condition. Check for a buildup of solids between the screen and the support areas on the shaker deck.

8.2 Screen Selection 1.

When possible, run the same screen mesh over the entire deck of a single deck shaker. When running different mesh cannot be avoided, the coarser mesh should be run at the discharge end. Do not vary the mesh size by more than one increment from feed to discharge.

2.

Select the finest screens which will give 70-80% fluid coverage on the shaker (Exception: See cuttings dryness discussion).

3.

Use the spreadsheet program, SHAKCAP, to assist in predicting shaker requirements to achieve a separation target of at least 100 mesh (149 microns).

4.

Always run the coarser screens on the top deck of a tandem deck shaker or on the upstream shaker. The upper deck screen should be at least two mesh sizes coarser than the bottom deck. It has been observed that running screens which are too fine on the top deck can actually impede cuttings conveyance on the lower deck.

5.

Select screens for which the new API designations are known to ensure predictable performance.

8.3 Cuttings Dryness The volume of drilling fluid lost with the discharged cuttings is becoming more important in the wake of increasingly stringent environmental regulations and more expensive drilling fluid formulations. In most cases, minimizing liquid waste from the shale shakers makes both economic and environmental sense. A field procedure to determine composition of the discharge is given in Appendix C, Solids Control Equipment Discharge Analysis, Oil-Based muds.

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Shaker discharge dryness is heavily dependent upon the size distribution of the cuttings and the viscosity of the mud. There will always be an irreducible “volume fraction” of fluid wetting the cuttings and this will vary inversely with particle size. Extremely fine solids have substantially higher percentages of associated liquid than larger solids due to surface area and surface tension effects. Mud viscosity will also impact the thickness of this fluid layer. The shaker can remove a portion of this residual wetness by the acceleration and impact forces imparted on the cuttings after they exit the pool region. Dryness may depend on the magnitude of these forces and the exposure time. Since a substantial portion of the shaker screening area can be covered by the liquid pool to achieve a desired separation, the remaining dry screening area may not be sufficient to remove excess moisture carried with the cuttings. High solids loading rates will also have a negative impact on cuttings dryness. Solids loading and dry screening area can be addressed during the planning phase by ensuring that sufficient shaker area is available to maximize cuttings dryness: 1.

When using SHAKCAP (see Appendix A, Solids Control Programs) to estimate shaker requirements, provide an additional shaker over the minimum number recommended by the program when shaker discharge dryness is critical.

2.

Install a cascading system or tandem deck linear motion shakers to reduce solids loading and fluid coverage.

The following remedial actions may help improve cuttings dryness: 1.

Deck Angle Increase - This is the most simple solution. Fluid loss along the hookstrips is reduced. Solids conveyance will decrease with steeper deck inclinations, which increases the contact time to remove excess moisture. Protection against whole mud losses due to flowline surges is also improved. The reduction in fluid coverage is not necessarily proportional to the deck angle selected. Because conveyance is lessened, the solids remain in the pool longer and can interfere with the ability of the fluid to pass through the screen, especially at higher solids loading rates. This may retard the formation of a shorter, deeper pool. Also, solids grinding may become a problem.

2.

High Efficiency Screens - Screens with high transmittance values will reduce fluid coverage and increase dry screening area. Two new screens, the Derrick “Pyramid” and Cagle’s “HCR” series offer distinct advantages in this application. The corrugated “Pyramid” design may reduce mud loss along the hookstrips and offers increased screening area. Cagle’s HCR cloth has very high transmittance values and has exhibited service life up to 4 times standard DX designs.

CONFIDENTIAL


January 1998

Shale Shakers

Page 32 of 36

3.

Schlumberger Dowell

Coarser Screens - This has two effects. First, the fluid endpoint on the shaker will recede, and second, the average discharged cuttings size will increase. However, this action usually carries with it the penalty of poorer separation efficiency and higher costs, unless downstream solids removal equipment “picks up the slack.” Try running a coarser screen at the discharge end before converting the entire deck to coarser screens. There are special considerations worth mentioning depending upon the mud system in use: Unweighted Muds The importance of fine screening in unweighted muds is typically not as critical, provided: 1) sufficient hydrocyclones and centrifuges are used, and 2) the cuttings are not soft and easily degraded by centrifugal pumps. In fact, significant fluid savings in oil-based muds have been realized by running coarser screens on the shakers to produce a dry discharge and transferring a greater share of the solids removal to the downstream centrifuges. Weighted Muds In weighted muds, the importance of the shaker in the solids removal system generally precludes the option of running coarser screens. Economics usually dictate that the finest separation possible be made by the shaker without substantial loss of barite in the discharge. Drill cuttings missed by the shaker will remain in the circulating system and eventually contribute to a low gravity solids buildup and subsequent viscosity increase.

4.

G Force Increase - Increased shaker acceleration will help remove excess liquid by overcoming part of the surface tension forces which bind the fluid to the cuttings. Conversely, cuttings conveyance velocity will increase and screen life will decrease. Conveyance velocity can be reduced by increasing the deck inclination, but screen life will decline considerably at accelerations above 4 Gs.

8.4 Sticky Solids (Gumbo) 1.

Use scalping shakers ahead of fine screen shakers. Circular or unbalanced elliptical motion shakers or shakers with short basket lengths are recommended as the scalping shakers. If space is limited, tandem deck linear motion shakers may be used.

2.

Use downhill or flat deck angles. Gumbo will not convey well uphill.

3.

Gumbo will not stick as persistently to wet screens. When spray bars are necessary to keep the screens wet, use low flow rate nozzles which produce a fine mist with an umbrella or fan-shaped discharge. These nozzles operate at less than 0.5 gpm. No more than two are normally required. Do not use high volume or high pressure sprays on a continuous basis. This will degrade the gumbo patties and drive the solids through the screens.

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Shale Shakers


8.5 Polymer Muds 1.

Prehydrate and preshear the polymer before adding into the active mud system to eliminate “fish-eyes” and blinding at the shaker.

2.

Select high efficiency screens to maximize the flow capacity of the shakers.

3.

Expect an overall reduction in shaker flow capacity of as much as 40%.

8.6 Blinding, Plugging 1.

Gilsonite (Asphaltenes) Triple-layer screens are susceptible to plugging by gilsonite or other asphaltene-based products in the drilling fluid. The problem may be mitigated by selecting single or double-layer screens. For example, on Derrick Flo-Line Cleaners, use the PBP HP or GBG HP series. Refer to Appendix D, Screen Designations, for a complete list of screen panel descriptions.

2.

Sand (Near Size) ·

Unbonded triple layer screens provide the best resistance to blinding, but screen life is generally poor.

·

Single layer, square mesh cloth is most susceptible to blinding. Select screen series with aspect ratios greater than 1.4. (Refer to Chapter 4, Shaker Screens.)

·

If excess shaker capacity is available, try running a finer screen. The sands may have a relatively narrow size distribution which might not blind a smaller opening size.

8.7 Lost Circulation Material 1.

Do not bypass the shakers to avoid screening out the LCM material.

2.

Scalping shakers can be used to recover LCM when concentrations are continuously required in the mud, provided:

high

·

Cuttings size distribution is sufficiently fine to pass through the scalping screens.

·

Solids loading rates do not negatively impact the performance of the downstream shakers and cause solids buildup in the active system.

·

The LCM removed by the scalpers is returned to the active system downstream of the centrifuge.

CONFIDENTIAL


January 1998

Schlumberger Dowell

Shale Shakers

Page 34 of 36

9 Estimating Number of Shakers Required 1.

Base the number of shakers required on the economics and the physical constraints of the specific application. A complete economic evaluation using SECOP is recommended.

2.

As a quick estimate, the spreadsheet file SHAKCAP can be used to estimate the number of shakers required or the performance of existing shakers.

3.

A “ballpark” estimate of shaker requirements, based on average drilling conditions can be made from Table 1. This is a very rough estimate and should be used only as a guide.

Table 1 Shakers Required Approximate Number of High Performance Linear Motion Shakers Maximum Viscosity (cP)

Circulation Rate (gpm)

5

10

15

20

25

30

40

50

60

300

1

1

1

1

1

1

2

2

2

400

1

1

1

2

2

2

2

2

2

500

1

1

2

2

2

2

3

3

3

600

1

2

2

2

2

3

3

3

3

700

2

2

2

2

3

3

3

3

4

800

2

2

2

3

3

3

4

4

4

900

2

2

3

3

3

4

4

4

1000

2

2

3

3

4

4

4

1100

2

3

3

4

4

4

1200

2

3

3

4

4

1300

2

3

4

4

1400

2

3

4

CONFIDENTIAL


Shale Shakers


10 Summary ·

The shale shaker is the only solids control device that makes a separation based on the physical size of the particle. The separation size is dictated by the opening sizes in the shaker screens. Hydrocyclones and centrifuges separate solids based on differences in their relative mass and the fluid.

·

Shale shakers with linear vibratory motion are preferred for most applications because of their superior processing capacity and finescreening ability. Circular motion or unbalanced elliptical motion shakers are recommended as scalping shakers in cascading systems.

·

Vibration of the shaker basket creates G-forces which help drive shear thinning fluids such as drilling mud through the screens. Vibration also conveys solids off the screens. Most linear motion shakers operate in the range of 3 to 4 G’s to balance throughput with screen life. G-force is a function of vibration frequency (rpm) and stroke length.

·

“High-speed” should not be equated with “high performance.” Laboratory tests indicate that, in the normal operating range for linear motion shale shakers, lower frequency vibration and longer stroke lengths improve throughput capacity. Most linear motion shakers operate at 1200 to 1800 rpm.

·

Avoid deck inclinations above 3°. High deck angles reduce solids conveyance and increase the risk of grinding soft or friable solids through the screens.

·

Shakers are designed to accept either hookstrip or rigid frame screen panels. Hookstrip screen panels are the most common and are usually cheaper, although cuttings wetness can be a concern due to deck curvature. Flat, rigid frame panels promote even fluid coverage, but can cost more.

·

Shakers may have single or tandem screening decks. Single deck shakers offer mechanical simplicity and full access to the screening surface. Single deck shakers may be arranged to process mud sequentially as a “cascading” system to improve performance under high solids loading conditions. Tandem deck shakers offer improved processing capacity under high solids loading conditions when space is limited.

·

Manifolds should provide even distribution of mud and solids to each shaker. Avoid branch tee’s. Recommended manifold designs are illustrated.

·

Operating guidelines are provided for optimizing screen life and cuttings dryness, handling sticky solids, polymer muds, blinding and LCM problems.

CONFIDENTIAL


·


Shale Shakers

Schlumberger Dowell

The spreadsheet program SHAKCAP can estimate the number of shakers required or to determine the screening capability of existing shakers. A complete economic evaluation using the SECOP program is recommended to determine the optimum shaker configuration when designing a system.

CONFIDENTIAL

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