How Parameters Affecting The Performance Of A Shale Shaker

The performance of a shale shaker depends on the large number of parameters. The most important variables affecting the capacity of a shale shaker are drilling fluid rheological properties, concentration and size distribution of solids, screen mesh and area, vibration frequency, vibration pattern, acceleration, and deck angle.

Drilling Fluid Rheological Properties

The maximizing capacity of a shale shaker is a trade-off between the content of separated cuttings off the screen and filtrated drilling mud passed through the screen.

For example, if the shaker deck is inclined downward to enhance particles transfer more drilling mud flows off the shaker channel and cuttings at the outlet have more moisture while tilting the screen up decreases solids velocity but more fluid is saved. There is an optimum angle for each shaker, depend on the manufacturer, which tilting the screen up more than that causes solids accumulation on the screen and blocking the screen pores. The physical mechanisms justifying the effect of vibration on the fluid displacement in porous media are not yet known.

It is suggested that an increase in flow rate is caused by changes in the pore structure and particle rearrangement. A research was conducted on the effect of vibration on the flow rate of drilling mud as a non-wetting phase in a column filled with water and sand, the mud flow rate increased by increasing amplitude.

Another explanation for the effect of vibration on the flow rate is based on the capillary trapping. The capillary trapping mechanism is the most promising one. The idea for this mechanism is based on the interfacial tension which is considered as the most significant parameter on multi-phase flow in porous media.

Drilling Solids(cuttings) Affect The Performance Of Shale Shaker

Changing in pore sizes of porous media trap the fluid which this leads to variations in capillary pressures. This pressure imbalance changes flow rate of liquid through the porous media. By applying vibration, we see that vibration of the screen will result in an inertial body force acting on the fluid which this movement pushes the trapped fluid to reflow. Vibration create an internal circulation in the mud and it gives more time to the fluid to touch the screen and this might be one of the effects of vibration on the enhancement of the flow rate.

Particle size distribution and concentration both have effect on the process of solids-liquid separation. Increasing the solid concentration in a drilling mud reduces the performance of the drilling operations. An experimental work shows that muds containing more than 10% by mass solids caused the failure in filtration process. Micro-bit drilling results indicated that very fine particles in a drilling mud have more adverse effects on the flow rate than larger sizes.

Shaker Screen Mesh And Area

It is claimed that particles smaller than 1μ are much more damaging to the filtration process than particles larger than 1μ. All solids-liquid separation tools in drilling industry are designed to remove particles larger than 1μ. The shale shaker changes the formation of particle structure in the drilling mud due to vibration. Shear stress of the drilling fluid is decreased due to vibration while polymeric drilling fluid is not affected by imposing vibration.

Table. 1 shows the size range of different types of particles in drilling fluid which can be separated in a shale shaker. A work by Cagle showed that an increase in drilling fluid viscosity decreases flow rate exponentially. It has been suggested that to maximize passing a viscous drilling fluid through screen openings, high frequency and low amplitude should be applied.

Table. 1. Drilling mud solids size range
Material	Size range μ
Bentonite	0.001-0.10
Barite	1-100
Drilled cuttings	1-1000

Drilling Fluid Viscosity

A research on the effect of plastic viscosity and yield values shows that plastic viscosity of drilling mud flowing through the screen and cake has significant effect on the capacity of a shale shaker while yield value has slightly effect on the performance. It has been also shown that increasing plastic viscosity and yield value of a drilling fluid increases the required screen area used in a shaker. Capacity of a shale shaker can be increased by decreasing plastic viscosity and increasing screen area, shaker angle, and acceleration.

Table 2 Important parameters for square Mesh shakers (Mesh # = # of openings pr. inch).
mesh	Wire Diameter	Opening Width	Smallest particle size removed
	Inches	Microns	Microns
10	.0250	2108	2000
20	.0160	863	800
60	.0072	230	205
100	.0045	140	125
120	.0037	117	105
200	.0030	74	68
325	.0018	44	40

Shale Shaker Motors And Deck Factors

The install location of the vibrating motors on the shale shakers can be considered as one of the parameters involving in the design of shale shakers. Some manufacturers say that if a vibrator is precisely mounted on the shaker support there is no need to incline the shaker downward to get desired mass rate of solids on the screen but one should aware that inclining the screen downward decreases the drilling mud flow rate and increases the moisture content of the particles leaving out the channel of the shaker.

In an experimental work done by Porter on a vibrating electromagnetic screen, the capacity improved by increasing frequency and decreased by amplitude. Their results showed that there is an optimum operational conditions which after passing the optimal point, flow rate decreased. Angle 33° was found as the most effective angle.

It has been shown that frequency is one of the important parameters affecting screen performance while other researches showed the reverse results. The interaction between frequency and particle size shows that for a feed whose particles size is close to the opening, frequency is the most effective parameter. Two experimental works claimed that screening efficiency decreased as frequency increased.

An increase in deck angle increased the effective mesh area and number of contacts per unit screen length. An increase in deck angle enhanced the passage of particles. It was found that angles more than 15° decreased the effectiveness.

G-force

An increase in deck angle increased the effective mesh area and number of contacts per unit screen length. An increase in deck angle enhanced the passage of particles. It was found that angles more than 15° decreased the effectiveness.

Shale shaker working in acceleration 4g and two frequencies 20 and 60 Hz showed that frequency has an insignificant effect on the fluid capacity of the shaker. His work showed that flow rate at 60Hz is slightly less than that in 20Hz. Their results on a 100*100 mesh screen with three types of drilling fluids showed that the capacity of a shale shaker depend heavily upon the acceleration.

A screen whose conductance is higher than the similar screens shows higher performance. The proposed mechanism for this improvement is in considering permeability and screen thickness than solely the pore area percentage.

The capacity of a shale shaker increases by increasing g-force. His work revealed that the rate of increase in capacity of the shale shaker
reached a minimum plateau. It indicates that there is a threshold g-force which after passing that point increasing acceleration does not have any effect on the performance of the shaker.