WAYS TO DECREASE PRODUCTION COSTS
FOR SUCKER-ROD PUMPING
-roughly two-thirds of the producing oil wells are on this type of lift.
-To maximize profits from these wells in the ever-changing economic situation with rising costs of electric power, installation designs must ensure optimum conditions.
IMPROVING ENERGY EFFICIENCY
energy losses both downhole and on the surface
must be minimized.
1- Downhole Energy Losses
2- Surface Losses
-The sources of down-hole energy losses in the
sucker-rod pumping system are :
-the pump, the rod string, and the fluid column.
The energy required for operating the polished
rod at the surface is thus
-the sum of the useful hydraulic work
performed by the pump and the downhole
energy losses.
-This power is called the polished rod power or
PRHP.
-The energy efficiency of the downhole
components of the sucker-rod pumping system can
be known by the relative amount of energy
losses in the well.
This is called Lifting Efficiency.
Surface Losses
mechanical energy losses Starting from the polished rod:
frictional losses arise in the stuffing box, in the pumping unit’s
structural bearings, in the speed reducer
(gearbox), and in the
belt drive.
the electrical power taken by the motor is always greater than
the mechanical power developed at the motor’s shaft.
The power losses in an electric motor are classified as mechanical
and electrical.
Mechanical losses occur in the motor’s bearings
due to friction.
other losses include windage loss consumed by air surrounding the
rotating parts.
an overall efficiency ηmot is used to represent
all losses in the
motor, which, for average electric motors,
Optimum Energy Efficiency
the energy efficiency is found from:
Where :
A more detailed formula
—the possible values of both the surface mechanical efficiency, ηmech,
and the motor efficiency, ηmot, vary in
quite narrow ranges.
—At the same time, their values are not easy to improve upon; that is
why. their effects on the system’s total efficiency are not very significant.
—On the other hand, lifting efficiency can be considered as the
governing factor since it varies in a broad range depending on the pumping
mode selected.
—Thus considerable improvements on the pumping system’s overall
energy efficiency can only be realized by achieving a maximum of lifting
efficiency.
—lifting efficiency mainly depends on the pumping mode selected (i.e.
the combination of plunger size, stroke length, pumping speed, and rod
string design).