Drilling Mud Circulation System

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

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