Mud Pumps and Circulating System
in Workover / Completion Operations
The Circulating System is one of major components of workover equipment. Its many purposes are
similar to the purposes of the Mud System.
These jobs must be done on all wells by the Circulating System:
• Control subsurface pressures
• Remove cuttings from the hole while milling or drilling
Fluid circulation should perform these beneficial functions:
• Clean, cool and lubricate the bit (mill) while drilling or milling;
• Protect pay-zones from possible damage;
• Circulate the influx out;
• Help buoy the weight of pipe.
1. Mud Pumps.
In this course the mud pumps and its components to be described by sufficiently simple and easily
understandable terms.
The brines and mud are circulated in the well by mud pump. The primary components of the mud pump
equipment include the following:
• Suction line components;
• Valves;
• Liners;
• Pistons;
• Pulsation Dampeners;
• Discharge line components.
Mud pumps are designed for pressure output, flow rate and horsepower requirements. High pressures
are required to circulate heavy fluids in the well and to optimize cleaning of hole bottom.
Flow rate must be sufficient to clean the bottom and well bore while circulating with water or low
viscosity fluids.
Pump suction efficiency must be high enough to assist the pump to keep discharge efficiency. If the
mud pump cannot gain access to the proper amounts of fluid when needed, its output will be less than
maximum for the particular pump rate. The two common types suction systems are atmospheric and
precharged.
Atmospheric pressure, which is approximately 15 PSI (140 kPa), is used in conjunction with hydrostatic
pressure to force the mud into the suction valves of the pump. This system is more effective as the height of
the fluid is increased. But long suction lines with many bends significantly decrease the effectiveness of the
system. In addition, gas-cut or high-viscosity fluids impede the system operation.
The successful method of correcting mud pump suction problems is the use of centrifugal pumps. The
addition of pre-charger offers many purposes: elimination of shock loads, smother operation, increased bearing
life and higher-speed operation.
The pre-charger also enables the mud pump to handle gas-cut or aerated fluids, giving better filling
characteristics with less chance of losing prime.
The triplex single-acting pump has three liners with valves on one end of the liner. Fluid is displaced on
the forward stroke only. The triplex pump has a smooth action that can pump at higher stroke rates even
though the volumetric output per stroke is less than the duplex pump.
The volumetric output of a pump on per-stroke basis depends on the stroke length, the rod diameter (for
duplex pumps), the liner size and volumetric efficiency of the pump.
For the single-acting triplex pump the volumetric output is calculated as:
API
Output in US barrels per stroke:
Vt = 0.000243 D2 L E
Where:
Vt = Volumetric displacement in BPS (barrels per stroke)
D = Diameter of the liner in inches
L = Stroke length in inches
E = Pump volumetric efficiency in % (percent)
SI
Output in liters per stroke:
Vt = 0.03861 D2 L E
Where:
Vt = Volumetric displacement in l/str (liters per stroke)
D = Diameter of the liner in inches
L = Length of stroke in inches
E = Pump volumetric efficiency in % (percent)
For a duplex double-acting pump, the volumetric output is calculated as:
API
Output in US barrels per stroke:
Vd = 0.001619 (2D2 – d2) L Ep
Where:
Vd = Volumetric displacement in BPS (barrels per stroke)
D = Diameter of the liner in inches
d = Diameter of the rod in inches
Ep = Pump volumetric efficiency in % (percent)
SI
Output in liters per stroke:
Vd = 0.025741 (2D2 – d2) L E
Where:
Vd = Volumetric displacement in l/str (liters per stroke)
D = Diameter of the liner in inches
d = Diameter of the rod in inches
L = Length of the liner in inches
E = Pump volumetric efficiency in % (percent)
*Rod sizes are often assumed to be 2 inches in diameter. It is best to measure the rod diameter or
check the manufacturer’s specifications.
Pump liners affect the pressure rating and volumetric output of the pump. The outer diameter of the
liner is a fixed quantity for a specific pump. As the wall thickness of the liner increases, the inner diameter
decreases, which reduces the volumetric output per stroke. In addition, the increased wall thickness of the liner
provides a higher pressure rating for the pump.
The discharge end of the liner has a set of valves. The discharge valve is located on top of and inside
the liner so the high-pressure discharge manifold can be connected easily to the valves. The suction valve is
generally located lower on the liner to decrease demands on the suction system. A duplex pump has a set of
valves on each end of the liner since it pumps in the forward and backward strokes.
Most operators prefer to run pulsation dampeners on the discharge end of the pump. The discharged
mud is under high pressure as it is forced out of the liners. It places significant surges on the equipment. The
pulsation dampeners are designed to absorb most of these surges and to reduce the wear of the other surface
circulating equipment. Dampeners are essential when running mud pulse MWD tools.
2. Centrifugal Pumps.
The centrifugal pump plays an important role in the circulating system as well as in all workover
operations. Among its applications are the following:
• Precharging the rig pumps
• Providing fluid to mud- or brine-mixing equipment
• Performing such functions as moving mix water, cleaning tanks, etc.
The centrifugal pump is a simple device. The primary component is an impeller that accelerates the
fluid into the discharge line. An engine or electric motor is attached to the drive shaft of impeller. The pump
must be completely primed prior to starting.