Tag: shale shaker

Posted on

CASCADE SYSTEMS

Cascade systems use one set of shakers to scalp large solids and/or gumbo from the drilling fluid and another set of shakers to remove fine solids. The first cascade system was introduced in the mid-1970s. A scalper shaker received fluid from the flowline and removed gumbo or large drilled solids before the fluid passed through the main shaker with a fine screen. The first unit combined a single-deck, elliptical motion
shaker mounted directly over a double-deck, circular motion shaker (Figure 7.17). This combination was especially successful offshore, where space is at a premium. It was, however, subject to the technology limitations of that time period, which made API 80 to API 120 screens the practical limit.
One advantage of multiple-deck shale shakers is their ability to reduce solids loading on the lower, fine-screen deck. This increases both shaker capacity and screen life. However, capacity may still be exceeded under

Figure 7.17. First cascade shaker system.

many drilling conditions. The screen opening size, and thus the size that
solids returned to the active system, is often increased to prevent loss of
whole drilling fluid over the end of the shaker screens.
Processing drilling fluid through shale shaker screens, centrifugal
pumps, hydrocyclones, and drill-bit nozzles can cause degradation of
solids and aggravate problems associated with fine solids in the drilling
fluid. To remove drilled solids as soon as possible, additional shakers
are installed at the flowline so that the finest screen may be used.
Sometimes as many as 6 to 10 parallel shakers are used. Downstream
equipment is often erroneously eliminated. The improved shale shaker
still remains only one component (though a very important one) of the
drilled-solids removal system.
A system of cascading shale shakers—using one set of screens (or
shakers) to scalp large solids and gumbo from the drilling fluid and
another set of screens (or shakers) to receive the fluid for removal of
fine solids—increases the solids-removal efficiency of high-performance
shakers, especially during fast, top-hole drilling or in gumbo-producing
formations, which is its primary application. The cascade system is used
where solids loading exceeds the capacity of the fine screens, that is,
it has been designed to handle high solids loading. High solids loading
occurs during rapid drilling of a large-diameter hole or when gumbo
arrives at the surface.

The advantages of the cascade arrangement are:
1. Higher overall solids loading on the system
2. Reduced solids loading on fine mesh screens
3. Finer screen separations
4. Longer screen life
5. Lower fluid well costs
There are three basic designs of cascade shaker systems:
. Separate unit concept
. Integral unit with multiple vibratory motions
. Integral unit with a single vibratory motion
The choice of which design to use depends on many factors, including
space and height limitations, performance objectives, and overall cost.

1 Separate Unit

The separate unit system mounts usable rig shakers (elliptical or
circular motion) on stands above newly installed linear motion shakers
(Figure 7.18). Fluid from the rig shakers (or scalping shakers) is
routed to the back tank of a linear motion shaker. Line size and potential
head losses must be considered with this arrangement to avoid overflow
and loss of drilling fluid. This design may reduce overall cost by utilizing
existing equipment and, where space is available, has the advantages of
highly visible screening surfaces and ease of access for repairs.

Figure 7.18. Separate unit cascade system.

2 Integral Unit with Multiple Vibratory Motions

This design type combines the two units of the separate system into
a single, integral unit mounted on a single skid. Commonly, a circular,
elliptical, or linear motion shaker is mounted above a linear motion
shaker on a common skid (Figure 7.19). The main advantages of this
design are reduced installation costs and space requirements. The internal
flowline eliminates the manifold and piping needed for the two separate
units. This design reduces screen visibility and accessibility to the drive
components.

Figure 7.19. Integral cascade unit with multiple vibratory motions.

3 Integral Unit with a Single Vibratory Motion

This design is shown in Figure 7.20. Typically, this device uses a linear
motion shaker and incorporates a scalping screen in the upper part of
the basket. The lower bed consists of a fine-screen, flow line shaker
unit, and the upper scalper section is designed with a smaller-width
bed using a coarser screen. Compared with the other cascade shaker
units, this design significantly lowers the weir height of the drilling fluid
inlet to the upper screening area. Visibility of and access to the
fine-screen deck can be limited by the slope of the upper scalping deck.

4 Cascade Systems Summary

Cascade systems use two sets of shakers: one to scalp large solids gumbo
and another to remove fine solids. Their application is primarily during
fast, top-hole drilling or in gumbo formations. This system was designed
to handle high solids loading. High solids loading occurs during rapid
drilling of a large-diameter hole or when gumbo arrives at the surface.
The introduction of high-performance linear motion and balanced
elliptical shale shakers has allowed development of fine-screen cascade
systems capable of API 200 separations at the flowline. This is particularly
important in areas where high circulating rates and large amounts of drilled solids are encountered. After either the flow rate or solids loading
is reduced in deeper parts of the borehole, the scalping shaker should
be used only as an insurance device. Screens as coarse as API 10 may be
used to avoid dispersing solids before they arrive at the linear motion
shaker. When the linear motion shaker, with the finest screen available,
can handle all of the flow and the solids arriving at the surface, the need
for the cascade system disappears, and the inclination may be to discontinue
the use of the scalping screen unit. Even when the fine screen can
process all of the fluid, screens should be maintained on the scalper
shaker. These screens can be a relatively coarse mesh (API 10 to API
12), but they will protect the finer-screen mesh on the main shaker.
The use of finer screens on the scalping shaker will result in fewer drilled
solids being removed by the scalping and main shakers.

Figure 7.20. Integral cascade unit with single vibratory motions.

Posted on

Shale shaker power system

The most common power source for shale shakers is the rig electrical power generator system. The rig power supply should provide constant voltage and frequency to all electrical components on the rig. Most drilling rigs generate 460 alternating-current-volt (VAC), 60 Hz, 3-phase power or 380 VAC, 50 Hz, 3-phase power. Other  common voltages are 230 VAC, 190 VAC, and 575 VAC. Through transformers and other controls, a single power source can supply a variety of electrical power to match the requirements of different rig components.
Shale shakers should be provided with motors and starters to match the rig generator output. Most motors are dual wound. These may be wired to use either of two voltages and starter configurations. For example, some use 230/460VAC motors and some use 190/380VAC motors. Dual-wound motors allow the shaker to be operated properly with either power supply after relatively simple rewiring. Care must be taken, however, to make certain that the proper voltage is used. Electric-motor armatures are designed to rotate at a specific speed. Typically the rotational speed is 1800 rpm for 60-Hz applications and 1500 rpm for 50-Hz applications.
Shale shakers use a vibrating screen surface to conserve the drilling fluid and reject drilled solids. The effects of this vibration are described in terms of the g factor, or the function of the angular displacement of a screen surface and the square of the rotational speed. (For a detailed discussion, see the preceding section on g factor.)
Angular displacement is achieved by rotating an eccentric mass. Most shale shakers are designed to be operated at a specific, fixed g factor by matching the stroke to a given machine’s rotational speed. It follows that any deviation in speed will affect the g factor and influence the shaker performance.
Deviations in speed may be caused by one or more factors but typically are caused by fluctuations in voltage or the frequency of the alternating current. If the voltage drops, the motor cannot produce the rated horsepower and may not be able to sustain the velocity needed to keep the eccentric mass moving correctly. Low voltage also  reduces the life of electrical components. Deviations in frequency result in the motor turning faster (frequencies higher than normal) or slower (frequencies lower than
normal). This directly influences rpm and shaker performance.
Slower rpm for a particular motor reduces the g factor and causes poor separation and poor conveyance. Faster rpm increases the g factor and may improve conveyance  and separation, but can destroy the machine and increases screen fatigue failures. In extreme cases, higher rpm may cause structural damage to the shale shaker. Thus, it is important to provide proper power to the shale shaker.
For example, a particular shale shaker is designed to operate at 4 g’s. The shaker has an angular displacement, or stroke, of 0.09 inches. This shaker must vibrate at 1750 rpm to produce 4.1 g’s. At 60 Hz, the motor turns at 1750 rpm, so the g factor is 4.1, just as designed. If the frequency drops to 55 Hz, the motor speed reduces to 1650 rpm, which results in a g factor of 3.5. Further reduction of frequency to 50 Hz results in 1500 rpm and a g factor of 2.9.
Most rigs provide 460 VAC, 60 Hz power, so most shale shakers are designed to operate with this power supply. However, many drilling rigs are designed for 380- VAC/50-Hz electrical systems. To provide proper g factors for 50-Hz operations, shale shaker manufacturers rely on one of two methods: increasing stroke length or  using voltage/ frequency inverters (transformers).
A motor designed for 50-Hz applications rotates at 1500 rpm. At 0.09-inch stroke, a shale shaker will produce 2.9 g’s. Increasing the stroke length to 0.13 inches provides 4.1 g’s, similar to the original 60-Hz design. However, the longer stroke length and slower speed will produce different solids-separation and conveyance  performance. At the longer stroke lengths, shakers will probably convey more solids and have a higher fluid capacity. Conversely, instead of increasing the stroke length, some manufacturers use voltage inverters to provide 460-VAC/60-Hz output power from a 380-VAC/50 Hz supply.
Constant electrical power is necessary for good, constant shale shaker performance. The tables below assist in designing a satisfactory electrical distribution system.
Alternating-current motors are common on most shale shakers. The motor rating indicates the amount of electrical current required to operate the motor. The values in Table 7.1 provide some guidelines for various motors. Be wary of all electrical hazards; follow all applicable regulatory codes, nationally, internationally, regionally, and locally, as well as manufacturer’s safety and installation instructions. The manufacturer’s recommendations should always take precedence over the generalized
values in these tables. The values in the tables are to be used as general guidelines only. Many factors, including insulating material and temperature, control the values.
The amount of electric current that a conductor (or wire) can carry increases as the diameter of the wire increases. Common approximate values for currents are presented with the corresponding wire size designation in Table 7.2. Conductors, even relatively large-diameter wire, still have some resistance to the flow of electric current. This resistance to flow results in a line voltage drop. When an electric motor is located in an area remote from the generator, the line voltage drop may decrease
the motor voltage to unacceptably low values. Some guidelines of wire diameter necessary to keep the voltage drop to 3% are presented in Table 7.3.

hp=horsepower; v=volts.
WARNING: Electrical Hazard—follow ALL national electric codes, local electric codes, and
manufacturer’s safety and installation instructions. Always conform to regulatory codes, as
apply regionally and internationally.

AWG=American Wire Gauge.
WARNING: Electrical Hazard—follow ALL national electric codes, local electric codes, and
manufacturer’s safety and installation instructions. Always conform to regulatory codes,
as apply regionally and internationally.

Posted on

Shale shaker design -g factor

The g factor refers to a ratio of an acceleration to Earth’s gravitational acceleration. Jupiter has a mass of 418.6*10^25 lb and Earth has a mass of 1.317*10^25 lb. A person on Earth who weighs 200lb would weigh 320 times as much on Jupiter, or 64,000 lb. A person’s mass remains the same on Earth or Jupiter, but weight is a force  and depends on the acceleration of gravity. The gravitational acceleration on Jupiter is 320 times the gravitational acceleration on Earth. The g factor would be 320. (As a point of interest, Mars has a mass of 0.1415*10^25 lb, so the g factor would be 0.107; a 200-lb person would weigh only 21.4 lb on Mars.)

Continue reading “Shale shaker design -g factor”