Mud circulation systems aim to retain desirable mud components by separating out solids and contaminants. There are four stages to remove solids from mud: 1) Screen separation using shale shakers and screens to remove up to 80% of solids, 2) Settling separation in non-stirred pits where heavy solids settle out, 3) Removing gas using vacuum degassers, 4) Forced settling using centrifugal devices like desanders and desilters that separate solids from mud using centrifugal forces. Proper solids control equipment and operation are needed to maintain an efficient mud system.

1. Petroleum Engineering
GEO 405
Bahria University
Department of Earth and Environmental Sciences
Mud Circulation System

2. Mud Circulation System
• Mud is made up of fluid (water, oil or gas)
and solids (bentonite, barite etc).
• The aim of any efficient solids removal
system is to retain the desirable
components of the mud system by
separating out and discharging the
unwanted drilled solids and contaminants.
Rabia, 2002

3. Mud Circulation Equipment
Solids Control Equipment
• Solids contaminants and gas entrapped in mud can
be removed from mud in four stages:
– Screen separation: shale shakers, scalper screens and
mud cleaner screens.
– Settling separation in non-stirred compartments: sand
traps and settling pits.
– Removal of gaseous contaminants by vacuum degassers
or similar equipment
– Forced settling by the action of centrifugal devices
including hydrocyclones (desanders, desilters and
micro-cones) and centrifuges.
Rabia, 2002

4. Mud Circulation Equipment
Solids Control Equipment
Rabia, 2002

5. Mud Circulation Equipment
Solids Control Equipment
Screen Separation Devices
• Shale shakers and scalper screens (Gumbo shakers) can
effectively remove up to 80% of all solids from a drilling
fluid, if the correct type of shaker is used and run in an
efficient manner.
• Mud laden with solids passes over the vibrating shaker
where the liquid part of mud and small solids pass
through the shaker screens and drill cuttings collect at
the bottom of the shaker to be discharged.
• There are two types of shaker operation: elliptical and
linear motion.
Rabia, 2002

6. Mud Circulation Equipment
Solids Control Equipment
Rabia, 2002

7. Mud Circulation Equipment
Solids Control Equipment
Settling Separation in Non-Stirred Compartments
• The solids control pits work on an overflow
principle.
• The sand traps are the first of the solids control pits
and are fed by the screened mud from the shale
shakers.
• There should be no agitation from suction discharge
lines or paddles.
• Any large heavy solids will settle out here and will
not be carried on into the other pits.
Rabia, 2002

8. Mud Circulation Equipment
Solids Control Equipment
Removal of Gaseous Contaminants
• Gas entrapped in mud must be removed in order to maintain the
mud weight to a level needed to control down hole formation
pressures.
• Gas is removed from mud using a vacuum degasser.
• The latter is a simple equipment containing a vacuum pump and
a float assembly.
• The vacuum pump creates a low internal pressure which allows
gas-cut mud to be drawn into the degasser vessel.
• As the gas moves toward the top of the degasser it is removed by
the vacuum pump.
• The removed gas is routed away from the rig and is then either
vented to atmosphere or flared.
Rabia, 2002

9. Mud Circulation Equipment
Solids Control Equipment
Rabia, 2002

10. Mud Circulation Equipment
Solids Control Equipment
Forced Settling by Centrifugal Devices
• Desanders and desilters are hydrocyclones and work on
the principle of separating solids from a liquid by
creating centrifugal forces inside the hydrocyclone.
• Mud is injected tangentially into the hydrocyclone and
the resulting centrifugal forces drive the solids to the
walls of the hydrocyclone and finally discharges them
from the apex with a small volume of mud.
• The fluid portion of mud leaves the top of the
hydrocyclone as an overflow and is then sent to the
active pit to be pumped downhole again
Rabia, 2002

11. Mud Circulation Equipment
Solids Control Equipment
Rabia, 2002