Rig Shakers

The rig shaker is the simpler of two types of shale shakers. A rig shaker (also called "Primary Shale Shaker" or "Coarse Screen Shaker") is the most common type of solids control equipment found on drilling rigs. Unless it is replaced by a fine screen shaker, the rig shaker should be the first piece of solids control equipment that the mud flows through after coming out of the hole. It is usually inexpensive to operate and simple to maintain.

Figure 3-13 Rig Shaker components

MUD TANK (POSSUM BELLY)

BELT. GUARD

LIQUID and FINE-SOLIDS DISCHARGE CHUTE

MOTOR

VIBRATOR ASSEMBLY

SCREEN

MOTOR

SCREEN

BELT. GUARD

LIQUID and FINE-SOLIDS DISCHARGE CHUTE

Possum Belly Rig

VIBRATOR ASSEMBLY

BASKET ASSEMBLY

BASKET ASSEMBLY

COARSE SOLIDS DISCHARGE

Standard rig shakers generally have certain characteristics in common (see Figure 3-13):

  • Single rectangular screening surface — usually about 4' x 5' in size. Some designs have utilized dual screens, dual decks and dual units in parallel to provide more efficient solids separation and greater throughput. Depending on the particular unit and screen mesh used, capacity of rig shakers can vary from 100-1600 GPM or more.
  • A low-thrust horizontal vibrator mechanism, using eccentric weights mounted above, or central to, the screen basket.
  • Vibration supports to isolate the screen basket from its skid.
  • Skid with built-in mud box (sometimes called a "possum belly") and a bypass mechanism.
  • Method of tensioning screen sections.

Screen sizes commonly used with rig shakers range from 10 to 40 mesh. Figure 3-14 shows the particle sizes separated by these mesh screens. In this graph the area to the left of each line represents solids which are smaller than that mesh size. These would pass through the screen and would not be removed. The area to the right of each line represents solids that are larger than the mesh size and would be removed from the mud.

In Figure 3-14, the area to the

Particles Solid
Figure 3-14 Particle Removal by Rig Shaker Screens

right of the 10 mesh line is confined, because it is limited by the size of the page. In actual usage, this area is unlimited. This means that a 10 mesh screen will remove all particles larger than 1910 microns — it doesn't matter if they are the size of BBs, marbles or baseballs — they will be removed and discarded by a 10 mesh screen.

Rig shakers are generally adequate for top hole drilling and for shallow and intermediate depth holes when backed up by other solids control equipment. For deeper holes and when using expensive mud systems, fine screen shakers are preferred.

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