LIFE OF A SHAKER SCREEN WHILE DRILLING

Author: Boma Femi Julius Category: Uncategorized
There are various factors to consider for a shaker screen to last while drilling, these factors affect the life of a shaker screen and are listed below-  
  1. Screen Motion
  2. The screen Technology
  3. Deck Angle Adjustments
  4. Suitable Scalping Deck screen
  5. Shaker Maintenance.
  6. Screen selection
  7. Drilling Flow rate
  8. Nature of Formation being drilled.
The above affects how long a shaker screen can be utilized before it is changed
  1. Screen Motion: we have Elliptical Motion, Balanced Elliptical (4.6 to 6.2 G’s), Circular (4 to 6 gs), and Linear Motion (7 to 8 g) types of shale shakers in use. With the most popular being Elliptical motion and Linear motion.
  • Elliptical motion – utilizes lower “g” (acceleration) forces and coarse screens reduce the solids separation; this motion makes screen life longer due to the lower forces and coarser screen run.
Linear motion – they have higher “g” (acceleration) forces (up to 8g) which gives excellent solids separation and reduces the fluid retention values for OBM on the cuttings generated. They come with many benefits, such as increased fluid handling capacity and increased ability to screen finer and faster, but due to the coupling of the finer screens and the higher forces from the shaker, they drastically reduce the shaker screen life. 
2. The screen technology: The technology of the shaker screen can be pyramid screen type or a conventional screen.
Vibration in the pyramid screen forces solids into troughs. In contrast, conventional screen solids form a continuous bed on the screen and impede fluid output, hence damaging the screen faster due to more retention time of cuttings on the screen. Also, screens made with rectangular mesh, unlike the square mesh, can be woven with heavier wires and subsequently have longer screen life. 
3. Deck Angle Adjustments: This affects the life of the shaker screens if the correct screen angle is not utilized. The fluid pool volume has to be kept small to increase the shaker screen life.
With increased screen angle, there would be a longer duration of cuttings on the screens, and the shaker screen life would be reduced. But when there is a decreased screen angle, it will require decreased fluid flow to overcome mud overflow, but it has the advantage of increased shaker screen life. The correct pool configuration has to be utilized. 
4. Suitable Scalping Deck screen: if an appropriate scalper size is used, larger, coarser abrasive solids that would load the bottom shaker screens and damage them would be reduced before it gets to the bottom screens hence prolonging the life of the screen
5. Shaker Maintenance: This has to be done diligently according to the manufacturer's maintenance schedule, as it affects the life of a shaker screen if not followed.
Failure to inspect the following: Bed rubbers, shock mounts, tension bolt assemblies, pneumatic bladders, hydraulic lines, etc., impairs the performance of the shaker when they are not replaced when worn or damaged. The end would be shorter life of the shaker screen, except the mud engineer has to screen down and run coarser screens for a given flow rate and ROP to compensate for bad shaker.   Channel protectors, cross and side supports, vibrating motors, jacking systems, etc., should be maintained as per the manufacturers’ schedule. 
6. Screen Selection: There has to be a balance between removing solids from the mud and the flow rate for the section being drilled, as wrong screen selection or incorrect sizing can result in shorter screen life or efficiency.
7. Drilling Flow Rate: Due to high drilling flow rate, which can damage shaker screens, a parallel process arrangement should be implemented to reduce the cuttings load on shakers, thereby increasing the life of screens, i.e., running more than one shaker to handle the flow coming from the wellbore, this will help process the large volume of cuttings.
8. Nature of Formation being drilled: Drilling large sand columns due to the abrasive nature of sand will damage shaker screens and might require screens to be changed after probably two days.
MUD ENGINEERS ROLE
The overall aim of the mud engineer as regards shaker usage is to remove unwanted solids from the mud and to lower well cost while doing so; he is limited with some of the factors listed above but can play the below roles to achieve longer screen life –
  1. Follow the mud program requirement for shaker screen sizes or use a screen selector calculator to select the appropriate shaker screen size for the hole section being drilled. This Is based on web-based computer programs using the rheological properties of the mud (PV, YP, MW), cut point (screen opening size), number of openings (provided by mfg.), percent open area, G’s, ROP, mud type, etc.
  2. Ensure the derrick man cleans the screens or makes adjustments while drilling to allow the screens to handle the fluid to mitigate Particle size plugging, which can limit screen capacity. When the screen has reached its solids-load limit, liquid-load limit, and particle size plugging due to fast drilling, there would be short life of the screen.
  3. The mud Engineer should Inspect the shaker screens after installation. If the screens are not properly installed and supported, they will quickly wear or tear.
  4. Follow up with rig or service company to carry out maintenance on shakers when it’s observed that shaker efficiency has declined.
  5. The mud engineer has to screen down and run coarser screens for a given flow rate and ROP to compensate for utilizing bad shakers to extend the shaker screens’ life.
  6. The mud Engineer should implement a parallel process arrangement to reduce the cuttings load on shakers, thereby increasing the life of screens, i.e., running more than one shaker to handle the flow coming from the wellbore; this will help process the large volume of cuttings.

CONCLUSION

The above considerations answer how long one would expect the shaker screens to last while drilling.

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