within the well. The whole system
is installed at the bottom of the
tubing string. An electric cable runs
the length of the well, connecting
the pump to a surface source of
electricity. The electric submersible
pump applies artificial lift by spinning
the impellers on the pump shaft,
putting pressure on the surrounding
fluids and forcing them to the
surface. An electric submersible
pump can lift more than 25,000
barrels of fluids per day (Rigzone,
2016).
The pump contains a plunger and
valve assembly to convert the
reciprocating motion to vertical fluid
movement. At the surface, the beam
pumping system moves to and fro,
connected to a string of rods called
sucker rods, which go straight down
into the wellbore. The sucker rods are
connected with the sucker rod pump,
which is installed as a part of the
tubing string near the bottom of the
well. As the beam pumping system
move back and forth, it operates
the rod string, the sucker rod and
the sucker rod pump, which works
in same way as the piston inside a
cylinder. The sucker rod pump lifts
the oil from the reservoir through the
well to the surface. It pumps about
20 times a minute; the pumping
units are powered electrically with
gas engine, called a prime mover.
In order for the beam system to
work properly, a speed reducer is
employed to ensure the pump unit
moves steadily. Its application covers
down-hole pressure wells, slim
holes, multiple completions, high
temperature and viscous oil.
Electrical Submersible Pump (ESP)
system uses a centrifugal pump
below the level of the reservoir fluids.
Tied to an electric motor, the pump
is made up of several impellers,
or blades, that move the fluids ESP is used primarily in very high
rate wells that can support higher
cost. With liquid-lifting capacities
up to 30,000bbls/d, depending on
electric power limitations, oilfield
submersible pumps are used
primarily for medium-and high-
volume production. ESP is the most
efficient and economical lift method
on a cost-per-barrel basis, but depth
and high GOR restrict its capacity
and efficiency. They are expensive
to purchase, repair and operate. The
Camco EOR group recommended
that ESP be retained as a primary
artificial-lift method and that
alternatives for reducing cost and
increasing production be reviewed.
Water-drive with very high water cuts
are typical applications for ESP.
Gas lift is an artificial lift method
in which gas is injected into the
production casing to reduce
hydrostatic pressure in the fluid
column, hence results in the
reduction of bottom-hole pressure
which allows the reservoir liquids to
enter the wellbore at a higher flow
rate. The gas-lift gas travels down
the production casing annulus
and enters the production tubing
through a series of gas-lift valves.
The gas-lift valve position, operating
pressures and gas injection rate
are determined by a particular
well condition. It is primarily used
offshore in deep wells and requires
minimum equipment unlike sucker
rod pump. Implementing a gas lift
system consists of injecting gas at
the bottom of the tubing: the gas is
mixed with the reservoir fluid which
decreases its density.
The column of fluid in the well
would become lighter and easier
to be lifted up to the well head.
Changing reservoir pressures, water
cuts, and formation gas rates can
be taken into account with the
initial design and because gas lift
equipment is durable, portable
and has few moving parts, it offers
a longer life compared to other
forms of lift. It poses low installation
and maintenance cost. It controls
production rates at the surface,
suited for deviations and horizontal
well bores and produced sand has
little effect on it. Oil production
enhancement will lead to increase
in oil recovery as a result of
optimization of the wells and result
in positive economic returns for the
company or operator of the field.
By Geoffrey Okotete (KSM)
VOLUME
lifting requirements and operational
objectives. Sucker Rod Pumping is
mostly used in onshore field because
of its bulk size and weight with the
huge depth and large volume of
fluids. The Sucker rod pump is the
most popular artificial lift methods,
with pumping system using a surface
power source to drive a down-hole
pump assembly. A beam and crank
assembly creates reciprocating
motion in a sucker-rod string that
connects to the down-hole pump
assembly.
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