CIRCULATING SYSTEM
A major function of fluid-circulating system is to remove the rock cuttings from the hole as
the drilling progresses. Drilling fluid is most commonly a suspension of clay and other
materials in water called drilling mud (will be discussed in details). The drilling mud travels
(1) from the steel tanks to the mud pump, (2) from the pump to the high -pressure surface
connections to the drill string, (3)through the drill string to the bit, (4) through the nozzle s of
the bit and up the annular space between the drill string and hole to the surface and (5)
through the contaminant-removal equipment back to the suction tank.The principal
components of the rig circulating system include
Mud pumps
Mud pits
Mud mixing equipment
Contaminat- removal equipment
MUD PUMPS
Mud pumps always have used reciprocating positive-displacement piston. Both two-cylinder
(duplex) and three cylinder (triplex) pumps are common. The duplex pump are generally
double-acting pumps that pump on both forward and backward piston strokes. The triplex
pumps are generally single-acting pumps that pump only on forward piston strokes
Triplex pumps are lighter and more compact than duplex pumps, their output pressure
pulsations are not as great, and they are cheaper to operate. For this reasons, the majority of
new pumps being placed into operation are of the triplex design.
The advantages of the reciprocating positive-displacement pump are
Ability to move high-solids-content fluids laden with abrasives (heavy duty pumps -
Ability to pump large particles -
Ease of operation and maintenance -
Reliability -
Ability to operate over a wide range of pressure and flow rates by changing the -
Diameters of the pump liners (compression cylinders) and pistons -
Long operating hours -
Capable to deal with wide range of mud (density (1 -2), viscosity (1-100 cP), particles -
(LCM-up to 10%)
Generally two circulating pumps are installed on the rig. For the larger hole sizes used on the
shallow portion of most wells, both pumps can be operated in parallel to deliver the large
flow rates required. On the deeper portions of the well, only one pump is needed, and the
second pump serves as a standby for use when pump maintenance is required
The flow conduits connecting the mud pumps to the drill string include, (1) a surge chamber
(2) 4- or 6-inches heavy-walled pipe connecting the pump to a pump manifold located on the
rig floor, (3) a standpipe and a rotary hose, (4) a swivel and, (5) a Kelly. The surge chamber
contains a gas in the upper portion, which is separated from the drilling fluid by a flexible
diaphragm. The surge chamber greatly dampens the pressure surge developed by the
positive-displacement pump. The discharge line also contains a pressure relief valve to
prevent line