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Virtual Session 1

Electrical Submersible Pumps Fundamentals

Basic ESP Components

Transformer

Switch Board

Vent Box

Wellhead Feed-thru connections

Round cable

Pump

Intake / Separator

Seal Section

Flat Cable

Motor

Downhole

Surface

═════════════════════════════════════════════════════════════════════════Electrical Submersible Pumps Fundamentals

© PetroSkills, LLC., 2016. All rights reserved._____________________________________________________________________________________________

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Functions of Main Components

ESP Downhole Components

The Pump

The function of the pump is to reduce the bottom-hole flowing pressure to gain more production

An ESP is a centrifugal pump and comprises a series of stages; so named because head added to fluid is largely due to centrifugal effects

Characterized by:• Small diameter• Large quantity of stages• High design loads

Electrical Submersible Pumps Fundamentals ═════════════════════════════════════════════════════════════════════════

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© PetroSkills, LLC., 2016. All rights reserved.

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The Pump

Normally driven by a two-pole submersible motor at an operating speed of 3,500 rpm (60 Hz power supply)

Performance:• Head = ƒ ( µ , glr )

– Viscosity and gas reduce head

• Flow = ƒ ( µ ) – Flow is reduced by viscosity

• Power = ƒ ( sg , µ ) – Power required by the pump

increases with density and viscosity

The Pump

The motor causes a shaft to rotate

The impellers (keyed to the shaft) turn with the shaft

Each rotating impeller adds kinetic energy to the fluid

The stationary diffuser slows down the fluid and converts kinetic energy to potential energy

The potential energy of the pump is measured in feet (or meter) of head or as a pressure differential across the pump

Impeller



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H-27ESP

PumpCurve

ESP PUMP Curve For 5-1/2” Well Casing

BHP

Head Capacity

Pump Efficiency

ESP Pump Curve

Radial flowMore head, less flowrate

Mixed flow

Axial flowLess head, more flowrate

Impeller Shape and Performance


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Radial Flow Impeller

Also called ‘pancake’ type

Vane angle close to 90 degrees

Usually for low flow rate

Low cost pump stages

Each stage compact• Pumps sections much shorter

than a pump section with same number of mixed flow stages

More prone to issues with gas, scale, solids and viscosity

Mixed Flow Impeller

Has vane angle close to 45 degrees

Usually for higher rates >1800 bfpd

Requires a lot more metal / stage

More tolerant of:• Solids• Scale• Gas• Viscosity



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Multiple Stages to Achieve Head

Single stage• Each stage comprises of an

impeller and a diffuser

Multiple stages• Multiple stages in series• Each stage adds some

head to the fluid• When length of the stacked

stages gets too large, the stages are grouped into multiple housings

Pump Performance Curve

Published by manufacturers for each pump type, showing:

• Head vs. flowrate• Hydraulic HP requirement• Efficiency vs. flowrate• Recommended operating

range for pump• Best Efficiency Point (BEP)• Usually produced for one

stage with fluid SG=1.0• Head curve is not affected

by the specific gravity of the fluid it is pumping

• More stages increase pump head; flowrate stays the same


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Typical Pump Performance Curve

Typical Pump Performance Curve: SI Units



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The Pump

Two construction methods for pumps:• Floater (original)• Compression

Floater• The impeller is free to “float” or move up and down relative to the

pump shaft• Does not transfer impeller hydraulic thrust to the seal thrust bearing

Compression• Built such that the impeller hubs stack together and transfer all thrust

to the seal thrust bearing instead of to the diffuser• This pump is a good choice for wells that pump experience downthrust

wear due to low flowrates• May have advantages for gas, abrasives, low fluid levels or

combinations of these problems

Floater / Compression Pumps

Floater CompressionStandard bearing High load bearing

Longer pump sections possible Maximum 80-100 stages per housing

Lower cost Higher cost

Only for smaller pumps Available in all pump sizes


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Impeller Hub

Bottom Shroud

Top Shroud

Impeller Skirt

Impeller Eye

Impeller Vane

Downthrust Washer

Upthrust Washer

Impeller Terminology

Pump Thrust

Under normal operating conditions, fluid recirculation on the top and bottom side of the impeller cause forces to be applied on the upper and lower impeller shrouds

When the recirculation forces are greater on the upper shroud, the impeller is moved down-Downthrust (head is too high)

When the recirculation forces are greater on the lower shroud, the impeller is moved up – Upthrust (flowrate is too high)

Operating with excessive Downthrust or Upthrust will cause inefficient operation and may induce vibration; leading to pump failure



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The Pump

Approximate thrust profile of a pump

0

BEP

Operating Range

Shut In Wide Open

Downthrust(positive)

STAGE FLOW RATE

Upthrust(negative)

+

-

The Pump: Performance Tolerances

API performance curve test tolerances• Pumps (new or re-run) should conform to published curves (within

certain ranges) as per the following


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Calculation of ESP Pump Stages Quiz

Well parameters (vertical)• Fluid = 35°API Oil• Water cut (%) = 0• Pump depth: 6500 ft. (1981.2 m)

• Mid Perf: 6750 ft. (2057.4 m)

• Casing pressure: 0 psig• THP: 150 psig (1034.214 kPa)

• Friction loss in tubing: 150 ft. (45.72 m)

• Fluid over the pump: 1200 ft. (365.76 m)

Calculate:1. Pwf, PIP and PDP2. The number of pump stages required,

if each stage develops a head of 58 ft/stage (17.68 m/stage)

Produced Fluid

Calculation of ESP Pump Stages Quiz

Calculate:1. Pwf, PIP and PDP2. The number of pump stages

required if each stage develops a head of 58 ft/stage

Produced Fluid

Pwf = 534 psi

PIP = 442 psi

PDP = 2598 psi

THP = 150 psiCHP = 0 psi

Solution

Gradient = 0.433*0.85 = 0.368 psi/ft (8.32 kPa/m)

Pwf = (1200 + 250)* 0.368 = 534 psi (3681.8 kPa)

PIP = 1200*0.368 = 442 psi (3047.483 kPa)

TDH = (6500-1200) +150 +408 = 5858 ft (1785.51 m)

∆P = 5858*0.368 = 2156 psi (14865.1 kPa)

PDP = 2156+442 = 2598 psi (17912.58 kPa)

Number of stages = 5858/58 = 101 Stages



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ESP Variable Speed Drive

A variable speed drive (VSD) provides flexibility to the otherwise fairly inflexible ESP system at a price

The Variable Speed Drive (also known as Variable Frequency Drive (VFD), Variable speed controller or Variable frequency controller) can change the rotational speed of the motor by changing the frequency of the AC power before sending it down hole to the ESP

Frequencies achievable with a VSD are from 20 Hz - 100 Hz

60 Hz

80 HzINOUT


By changing the rotational speed of the pump, the operating range expands

An increase in Hertz• Increases RPM• Increases pump head• Increases the HP requirement


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Pump / Motor Speed Variation Laws

Pump affinity laws** • May be driven at other speeds either due to power

source or intentionally to modify performance– Flow = ƒ (rpm) = ƒ (frequency)

– Head = ƒ (rpm2) = ƒ (frequency2) – Power = ƒ (rpm3) = ƒ (frequency3)

Motor: The rotational speeds and the horse power (HP) produced by motor are proportional to Hz to the first power:

• A 250 HP motor spinning at 3500 rpm with 60 Hz supply

– Increase frequency from 60 to 66 Hz

– Speed will increase to 3850 rpm, and

– Will produce 275 HP

** Note: These are pump laws and not motor laws

The Pump

Pump affinity laws for ESP (at BEP)

Motor performance (HP developed)

)(

)(

)(

3

1

212

2

1

212

1

212

N

Nbhpbhp

N

NHH

N

NQQ

)(

)(

1

212

1

212

N

NHPHP

Hz

HzNN



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The Pump

The Tornado plot shows the pump performance and range at different Hz

0

100

150

200

50

0 20 40 60 80 100

Frequency (Hz)

HP


The motor horsepower output is a function of frequency, varying in a straight line slope

Motor : HP2 = HP1 * (Hz2 / Hz1)


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0

100

150

200

50

0 20 40 60 80 100Frequency (Hz)

HP


The pump horsepower required is a function of rotational speed (frequency) cubed

Pump : HP2 = HP1 * (Hz2 / Hz1 )3

0 20 40 60 80 1000

100

150

200

50

Underloaded Overloaded

Frequency (Hz)

HP


This gives an upper limit to the range of frequency allowed to a given ESP system

Up to a certain frequency, the motor is underloaded, and, beyond that frequency, the ESP cannot be operated because the motor is overloaded



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Examples of Max Shaft BHP/Housing DP

Centrilift shaft/housing ranges

Pump Series Shaft (Max bhp) Housing (DP)

338 110/240 4,310

400 110/240/550 5,020

513 550 4,970

562 1017 3,510

675 1017 2,680

875 1017 4,315

1025 1500 3,054

Shaft rating is based on 60 Hz operation

On VSD operation, shaft rating varies with (Hz/60) ratio

How Rates May Vary Within Pump Series

Centrilift capacity ranges

Pump Series Diameter Flow Range (bpd)

338 3.375” 550 – 3,100

400 4.000” 150 – 6,800

513 5.125” 750 – 12,000

562 5.625” 9,500 – 24,000

675 6.750” 4,500 – 44,500

875 8.750” 10,300 – 32,200

1025 10.250” 19,200 – 58,900




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Pump Curve Quiz

For the pump GC 4100 Wood Group, find: • The head per stage, horse power requirement and the

efficiency while pumping 4500 BFPD• Is the pump on Upthrust or Downthrust under these

conditions? Is this acceptable?• What is the fluid rate corresponding to the BEP?• What will happen to the power requirement of the pump if the

SG of the fluid increases by 8%

Pump Curve Quiz



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Pump Curve Quiz

BEP

40.5 ft

4500

Solution

65%

2.05HP

Pump Curve Quiz

For the pump GC 4100 Wood Group, find: • The head per stage, horse power requirement and the efficiency

while pumping 4500 BFPD40.5 ft/stage (12.34 m/stage)2.05 HP/stage (1.5287 kW/stage)65% Efficiency

• Is the pump on Upthrust or Downthrust under these conditions? Is this acceptable?

Mild Upthrust, acceptable• What is the fluid rate corresponding to the BEP?

4100 BPD (651.85 m3/day)• What will happen to the power requirement of the pump if the SG of

the fluid increases by 8%The HP demand will increase by 8%

Solution


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Gas Handling

Excessive gas at pump intake can: • Create gas lock• Reduce bearing life• Decrease flow, head, efficiency • Reduce the cooling of the ESP system

Three basic methods to minimize gas entry into pump:• Avoidance• Separation• Handling

Gas avoidance:• Bottom feed intake systems• Shrouded systems

Gas Separator

Gas separator• Used in applications where free gas

causes interference with pump performance

• Units separate some of free gas from fluid stream entering pump to improve pump’s performance

Rotary gas separator • Specially designed rotating chamber

acts as centrifuge• Forces the heavier fluid outside and

allows free gas to migrate to the center of the chamber

• At the top, two streams are physically separated

• Liquid rich stream is ported internally to the pump inlet

• Gas rich stream is vented to the casing annulus



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Gas Separator

Use gas separators when …• Free gas % is more than 10% with radial flow

stages• Free gas % is more than 15% with mixed flow

stages– Approximate rotary separator efficiency could be

50-90%

• Vortex gas separator may be used where production of abrasives/solids through the pump is a possibility

Notes:• After separation, free gas going into the first

stage should be less than the above percentages

• Very gassy wells may require a tandem separator or advanced gas handler

• Sandy wells requiring a rotary gas separator should utilize specially design abrasion resistant units or another form of gas handling technology

Gas Separator: Has Rate Limitations

Rotary gas separator ranges (note, flowrate expressed as BPD)

Series Intake Flowrate, BPD (Max)

338 2,700

400 4,400

513 13,000

675 25,000




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Advanced Gas Handlers

Homogenize the gas and liquid before it enters the pump, reducing the tendency of gas locking

• Able to handle 45% of gas volume fraction under normal conditions• Use in tandem with gas separators to increase the gas handling

capability• The Poseidon gas handling system (helicoaxial multiphase pump)

primes the main production pump and pushes the gas-liquid flow stream into the stages, reducing gas volume by compression (can handle up to 75% GVF)

GAS HANDLING CAPABILITY

Device Gas Volume Fraction [V/(V+L)] %

Radial Flow Stage

Mixed Flow Stage

Single Vortex Gas Separator

Single Rotary Gas Separator

Advanced Gas Handler

Tandem Vortex Gas Separator

Tandem Rotary Gas Separator

Tandem Vortex Gas Separator + Advanced Gas Handler

0 10 20 30 40 50 60 70 80 90 100

Seal / Protector

Located between pump and motor

Function• Balances pressure between motor

and wellbore• Transmits force from motor to pump• Protects motor from contamination

by well fluid• Absorbs thrust from pump

Nomenclature• Seal = Centrilift• Protector = Reda / WG



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Seal / Protector

Steps in the operation cycle of a protector:

• Servicing the protector prior to installation

• System landing at setting depth, oil expands

• Motor operates, oil expands more• Motor stops, oil contracts• Motor operating cycles• Pulling the unit to surface, oil contracts

The motor should remain filled with the special blend oil that lubricates and electrically insulates the components

• The equalizer should permit expansion / contraction of the motor oil

Protector Types

Positive Seal Protector Labyrinth Seal Type

Well fluids

Motor fluid

Flexible bag


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Protector Types

Flexible Bag type• Flexible bag to handle the

variation in motor fluid volume• Elastomer selection critical• Provides complete isolation

Protector Construction• Series / parallel• Multiple chambers• Thrust bearings in base of assembly

Labyrinth Seal Type• Better in vertical wells• Works on the principle of U-Tube• Depends on separation of fluids -

significant difference in specific gravities between motor and well fluid required

• Not recommended for horizontal wells

Seal / Protector

Mechanical seals• Usually John Crane• Allow slight leakage for lubrication of

shaft• Prevent passage wellbore

Thrust bearing• Thrust runner fixed to shaft• Rides on Upthrust or Downthust

bearings• Shimming critical in compression

pumps

Downthrustbearing

Upthrustbearing

ThrustRunner



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Motor

Motor is oil filled (dielectric)

It is a two-pole, three phase, 3,600 RPM design (60 Hz)

Some motor components are designed to withstand up to 500oF temperatures

Motor cooling is achieved by:• Internal oil circulation• Flow of well fluid along outside skin (min

velocity of fluid past motor 1ft/s)

A shroud is used if:• ESP is set below perforations• Or, to improve the fluid velocity past the

motor (by reducing the clearance area between the motor and the casing)

Stator Laminations

Kapton-Wrapped Magnet Wire

Rotor

Bearing with T-ring

Housing

Epoxy Encapsulation

Motor

Motor components


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Motor

Name plate on motor

Motor

Motor component parts



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Function of the motor • 3-phase alternating current creates

revolving magnetic fields in stator• Magnetic fields cause rotor and shaft

inside stator to spin• Each rotor is then capable of

producing X number of horsepower with given voltage

Voltages, on surface, may be changed to adjust horsepower capabilities and performance of motor (within limit)

• Motor speed = f (frequency)• Horsepower = f (frequency)

Motor

The induction motor synchronous speed can be calculated when the number of poles (2 in this case) and frequency of supply is known:

Due to losses due to slip, friction and windage, the motors run at lower speeds:

Large HP requirements may be met by bolting more than one motors together as tandem motors

Hz x 120

Number of Poles

Motor Speed

RPM =

Supply Frequency Synchronous Speed Actual Speed

60 Hz 3600 RPM 3450 RPM

50 Hz 3000 RPM 2915 RPM


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Motor

Motor performance curve

Motor Performance Curves: Reda 562 Series 60 Hz

50% 60% 70% 80% 90%

Percent of Nameplate Load100%40%

Amperage% Efficiency

% Power Factor

Voltage

Speed RPM

3450

3500

3600

83

87

86

90

89

88

85

84

82

20

40

60

80

100

87

86

84

81

3400

83

355085

82

50% 60% 70% 80% 90%

Percent of Nameplate Load40%



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Motor

Total motor load = Pump load (Brake HP) +

Intake load (Brake HP) +

Seal section load (Brake HP)

Motor selection• For one HP rating there are

usually several NPV, NPA possibilities

• However most choose the highest voltage to minimize losses in the cable

• Check motor rotation using a phase rotation meter before running in hole

Motor

Amp chart - motor amps with time

• Amps to motor can be diagnostic to pumping condition

• Computer may just record linear trace instead of using amp chart

FactorPowerEfficiencyVolts

fluidofgsstagesofnostage

HP

Amps

..


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Motor

Motor sizes

Motor Series Diameter HP Range

375 3.750” 19 – 195

450 4.500” 15 – 306

544 5.438” 18 – 75

562 5.625” 38 – 920

725 7.250” 175 - 750

HP range is based on 60 Hz operation

On VSD operation, motor hp varies with (Hz/60) ratio

ESP Design Resource Material

Refer to the Engineering

Training resource material

from Centrilift to assist

understanding of

performance characteristics

of various ESP components

and their limitations



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