SOCIETY
OF PETROLEUM ENGINEERS
Mid-Continent Section, Tulsa, Oklahoma
Abstracts courtesy of Ken Saveth, ksaveth@juno.com
Instrumented PC Pump Charge Pump - Came Matthews: Centre for Frontier Engineering Research, Inc.
What is a PC Pump Charge Pump?
A tandem arrangement of a larger capacity PC charge pump located below a smaller capacity main PC pump.
The charge pump is typically short & has limited pressure capacity.
The two stators are separated by a 10’ (3 m) pup joint.
The stators are run on the tubing string while the rotors are run with the rod string.
The way that the system is configured is such that the charge pump (bottom pump) is a high volume/low pressure pump & the main pump (top pump) is a high pressure/low volume pump. Some typical BMW Charge Pump configurations are as follows:
Model 10 main pump, model 16 charge pump (1.6:1)
Model 28 main pump, model 56 charge pump (2:1)
Model 28 main pump, model 83 charge pump (3:1)
As for the pump design, the main pump is designed for full lift requirements while the charge pump typically provides 200 m of lift. The rotors can consist of one of three lengths - Std., extra long, & extra extra long. The Charge pump would typically be applicable in gassy wells & high sand cut wells. Sizing considerations for the Charge Pump are typically lower speed applications. The main pumps are sized for standard fit for the designated application. IN comparison, the charge pump is usually sized to 75 - 80% efficiency at rated pressure. Used pumps are frequently cut up for use as charge pumps.
In gassy wells, the effect on the produced gas is that due to the higher pressure in the pup joint between the charge & main pumps, the gas is forced back into solution thereby making the main pump operate more efficiently.
In installing a PC Pump Charge Pump system, there are several items to consider.
In vertical or deviated wells, the charge pump is seated below the perforations.
In horizontal wells, the system is run as low as possible.
The weight of the rod string is usually sufficient to land the rods.
Loading of the tubing is required in some cases.
Charge pump rotor is equipped with a "bullet" tip to assist installation in horizontal wells.
A field application was conducted in EnerMark’s Maidstone field which is in Western Saskatchewan. The field characteristics are as follows;
Reservoir - McLaren
Depth - 490 m
Reservoir Pressure - 3,500 kPa
Net Pay - 3 m
Oil Gravity - 15° API
Viscosity - 3,000 cp @ 20° C
Kh - 2,000 md
Kv - 200 md
Soi - 80%
GOR - 40 m3/m3
The typical well configuration was:
Casing - 219 mm (8 5/8") J55
Seating Depth 575 m @ 90°
Liner - 139.7 mm (5 1/2") J55, slotted
(100 - 250 slots/m)
KOP - 310 m
Build Rates - 8 - 12°/30 m
The typical production string consisted of a tubing anchor, BMW 56-200 charge pump with tag bar, a 3 m x 89 mm pup joint, a BMW 28-1200 main pump, & a tubing swivel assembly. The rod string consisted of a BMW 56-200 rotor, a 22.4 mm (7/8") pony rod, a BMW 28-1200 rotor, 2 standard c/w centralizers, a 26,000# Corod shear, & #6 continuous rods.
In order to monitor the system, a customized housing was designed with pressure ports to the charge pump discharge as well as the wellbore & main pump discharge.
We can summarize the field test results with comments on specific items as follows:
Operating PC pumps at low efficiency due to high gas production substantially reduces service life.
Load variations due to produced gas may cause fatigue failures of sucker rods.
Charge pumps have proven effective in improving pump efficiencies & production rates in several horizontal wells.
Charge pumps have been in continuous use at EnerMark’s Maidenstone operation for up to two years without experiencing a failure.
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