The evolution of dewatering systems for CBM/CSG

applications – past, present and future: motivation for a

new ESPCP design

Lyon van der Merwe and Attie Jonker Don Brown

Franklin Electric SA (pty) ltd Franklin Electric Inc.

South Africa USA

13 Engwena Road, Sebenza, South Africa, 1610 400 East Spring Street, Bluffton, IN, 46714

lvandermerwe@fele.com dbrown@fele.com

Abstract – The history of tight gas artificial lift systems

are discussed from a period and technology point of view.

Practical aspects of the particular dewatering process

(artificial lift process) are considered. The impact of new

pumping technologies and modern control gear and system

management principles are elaborated on. The advantages of

comprehensively designed system solutions with respect to the

particular application are discussed.

Index Terms – Artificial lift, coal bed methane, coal seam

gas, dewatering, systems.

I. INTRODUCTION

While coal bed methane or coal seam gas (CMB/CSG)

operations are associated with the oil and gas industry,

several aspects of such operations justify viewing the

dewatering process or hydrostatic pressure reduction or

artificial lift operation from a more conventional ground

dewatering perspective. The significant amount of

descriptive terms for the process is already a clue to the

overlap of the same functional requirement, albeit

approached from a different industry. At no time however,

should the requirements in the CBM/CSG production

industry with respect to safety, reliable operation be ignored.

In fact, additional effort should be considered to increase

safety, reliability, time between work overs and

serviceability.

A. Artificial lift

Artificial lift or the reduction of hydrostatic pressure is

required in cases where the natural gas pressure formed in

the coal seams cannot overcome the hydrostatic pressure. It

is also advantageous to reduce the hydrostatic pressure in

order to increase gas production.

1) Artificial lift process: The process of artificial lift

provides external energy to create additional drawdown on

the formation. This can be achieved with a rod pump, a

progressing cavity pump (surface driven – PCP or

submersible driven - ESPCP), an electrical submersible

pump (ESP) or gas compression.

2) Typical dewatering requirement: CBM/CSG

applications require (potentially) a widely varying range of

artificial lift or dewatering requirements – from several

hundreds of barrels of water per day to only a few barrels of

water per day. Irrespective of the rate of pumping, it should

always be under controlled conditions.

3) Multiple well environments: Another characteristic of

specifically CBM/CSG operations are the use of multiple

wells in (often) close proximity. Therefore, when

considering artificial lift requirements in such applications a

multiple well viewpoint should rather be considered, as

opposed to single well operation. Several advantages could

be obtained when operating from a more holistic point of

view.

II. HISTORY OF CBM/CSG DEWATERING

The CBM/CSG industry found its origin in the oil and gas

industry. This is especially relevant since, notwithstanding

the nature of the oil and gas industry with respect to safety

and reliability, CBM/CSG application are associated with

deep settings, high pressures, and high powers and is based

on trusted and reliable product and long term experience.

A. Early days

During the early days of CBM/CSG the artificial lift or

dewatering equipment used, mostly stemmed from the oil

and gas industry to which the CBM/CSG industry belongs.

Fig. 1 Beam pump

Figure 1 is a picture of a beam pump. The use of oil and gas

industry equipment was due, mainly to the need for deep

settings, high operating pressures and large power levels. In

CBM/CSG applications the need to dewater relatively deep

coal seams (usually far below the useful groundwater level)

meant that the more conventional well or borehole

equipment could not easily meet the CBM/CSG dewatering

needs. Often the balance between operating power levels and

the need for high starting torque also influenced and biased

the use of oil and gas artificial lift equipment in the

CBM/CSG industry.

Fig. 2 Surface driven progressing cavity pump (typically 2-3 meters off the

ground).

However, these products were trusted and had long term

records of reliability and were technologies that was well

understood, meaning that expertise were available to operate

and service the equipment. In fact that is still true for today.

B. Later development

Eventually the products used in conventional water well

pumping applications found its way into the CBM/CSG

industry – including the necessary modifications with respect

to materials, robustness and adaption of pressure and flow

characteristics.

Fig. 3 Electrical submersible pump (ESP), typically used in the

conventional water well industry, applied to a CBM/CSG application

(typically 0.5 meters off the ground).

During the 1990’s the USA CBM/CSG market started to us

conventional water well pumping equipment extensively.

Figure 3 is a picture of such an ESP installation. It became

apparent that while higher power levels may be required

during initial the dewatering stage, the production phase

requires reduced power levels to pump lower volumes of

water.

C. Today

If history is a measure to go by, the CBM/CSG artificial

lift market, served by a mixture of traditional oil and gas

pumping equipment and more conventional water well

equipment, will see a continued gradual progressing towards

using more conventional water well pumping equipment.

One reason for the effective use of progressing cavity pumps

stem from the need for a very wide range of duty points with

respect to operating pressure, considering that the

CBM/CSG dewatering application requires pumping down

water levels, sometimes ranging from ground level to levels

of 500 to 1500m below surface.

On the other hand the CBM market in the USA has been

using centrifugal submersible pumping systems for a

significant number of years. To support this market the

continuous improvement in the electric motors and

centrifugal pumps to address this need has led to the

development of dedicated submersible motors and pumps

for the CBM/CSG market.

The confluence of the latter with effectively 40-50 years’

experience in the progressing cavity pumping industry has

resulted in an exciting new development that will make a

substantial contribution to the CBM/CSG market.

III. PRACTICAL ASPECTS OF THE ARTIFICIAL LIFT PROCESS

In CBM/CSG dewatering applications several aspects,

contrary to conventional water well pumping need to be

dealt with. Solids handling is an important issue. The

CBM/CSG application does not deal with clean water

pumping. Hence a suitable pump needs to be able to manage

especially fracture sand, coal fines and even larger coal

particles. Additionally, one needs to deal with gas entrained

water when dewatering coal seams. The level of gas-cut is

often unpredictable and variable. Thirdly, unknown water

conditions (varying pressure conditions and flow rates) make

it difficult to size pumps and control it. Water quality and

chemical composition also complicate the application. It is

also important to consider the surface impact of the pumping

equipment. Since multiple wells (vertical or horizontal) are

often required a reduction in surface impact will always be

welcome. Another significant consideration with artificial

lift systems for CBM/CSG would be operating cost per well,

as cost can add up rapidly when considering a multitude of

wells.

A. Solids handling

Possibly one of the most important design features in the

Franklin Electric pump is the exclusive heavy duty ball

check valve. See figure 4. This feature prevents any possible

backspin and if any sand is present in the rising main, it will

settle on top of the check valve. The PC pump is designed to

produce enough pressure with the next start-up that it will

discharge the sand to the surface.

A further consideration for any installation is to use the

smallest diameter pipe possible with the correct

specifications to ensure that the highest water velocity

possible is achieved, to move any frac sand and/or coal fines

through the discharge. Features such as these contribute

substantially to the success of the ESPCP design, as has been

proven in case studies. See later on. Pumps pulled for

routine inspection contained up to 10m of pipe above the

pump filled with frac sand and coal fines.

Fig. 4 Electrical submersible progressing cavity pump (ESPCP)

construction

The case studies also revealed that ON/OFF operation of the

pumps could be implemented (maintaining a reasonable

cycle time to avoid motor damage) without any noticeable

start-up difficulty. This mode of operation, together with the

normal continuous mode of operation over the complete

speed range makes a large turndown ratio in volume pumped

possible. See Figure 5. [1]

Fig. 5 ON/OFF control – the saw tooth bold line shows the water level.

Figure 5 also illustrates the possibility of controlling the

maximum pump speed (high flow rate pulses in the first half

of the graph) to ensure sufficient fluid velocity thereby

transferring suspended solids to surface. The ON/OFF mode

of operation is made possible by the heavy duty ball check

valve design.

One parameter that influences the pump selection is the

minimum flow characteristics. Conversely, the selected

pump minimum flow may be chosen based on critical tubing

velocity. As discussed in [3], if the tubing flow velocity is

less than the critical transport velocity of the sand/coal

particles, it will settle out in the tubing above the pump. In

the case of the new ESPCP design the settling will take place

on top of the check valve, preventing particles from settling

in the rotor stator. Particle accumulation can also create a

partial or complete blockage 9as experienced in case studies

undertaken) in addition to increasing the overall fluid

density. Any of these situations will cause higher pump

discharge pressures.

In the example below the graph represents the critical tubing

rate for various U.S. standard sheave sizes. See figure 6. If

tubing flow rates fall below this line, there is a strong

possibility that the velocity will not be sufficient to transport

that particular particle size to surface. Therefore, as the

required dewatering needs drop to below this minimum

continuous rate of pumping, an ON/OFF mode of operation

may prove useful and in fact desirable, given that the ON

time makes provision for at least one tube volume being

displaced per cycle.

Fig. 6 Critical Sand Settling Rate for specific riser area (approximately 4

square inches) [3]

B. Entrained gas

Laboratory tests [2] conducted during the development

of the ESPCP show that a gas cut of up to 60% results in

only a 25% loss in flow rate and even less at maximum

operating pressure. See figure 7.

Fig. 7 Electrical submersible progressing cavity pump (ESPCP)

construction

C. Unknown water conditions

Widely varying water flow rate requirements and a large

variation in required pressure management make it difficult

to select one pump through-out the life of a CBM/CSG well.

However, during the initial stages of the well’s life it will be

helpful to reduce pump change-outs to a minimum. The new

ESPCP design, in combination with the necessary control

system can increase the dynamic range of the first pump

installed to reduce work-over requirements. Figure 8 shows

the range over which the required water production may

vary.

Fig. 8 Exponential decline of water in a typical well [4]

Since the pump design provides for ON/OFF operation (ball

check valve) this mode of operation can be used in closed

loop control to achieve control of the desired parameter

(water level or bottom-hole pressure or any other parameter

that is used to control the operation of the well) by

maintaining an average set value. This mode of run time

modulation can be used until the flow rate during the ON

time drops below the critical tubing velocity. It must also be

noted that the pump design needs to take starting

characteristics of the pump into consideration as well, to

make frequent starting possible without creating potential

high starting torque situations but at the same time maintain

high levels of efficiency. See figure 9.

Figure 9 Large turndown ratio operation

D. Surface impact

Since several wells may be required on a CBM/CSG

field, the surface impact will play an important part. Figure

10 is an illustration of a rather innovative way of

camouflaging large surface components, while figure 11

illustrates an installation of the latest ESPCP technology.

Figure 10 Rod pump in children’s play park

Figure 11 Reduced surface impact, incorporating significantly more

operating information

This installation incorporates telemetry, well control, data

concentration and communication, integrated into a single

system.

The correct control system will also reduce the need for

regular site visits and surface disturbance. Remote control

and data collection ensures that site visits are undertaken on

a need to basis only.

E. Well operating cost

While initial CBM/CSG artificial lift installations made

use of large (10’s kW) installations, the selection of the

correct pumping equipment can reduce both capital and

operating costs substantially.

Results obtained from recent installations show that typical

power levels can be as low a 600W- 3kW to maintain the

correct water levels at depths of 280m - 480m. Control

panels with drives and motors rated at 7.5kW are used in

these applications. Substantially oversized equipment will

result in poor efficiencies, higher input power levels and

increased operating cost.

Nevertheless provision should be made for the necessary

starting torque and control to ensure reliable operation. High

starting torque capability and high operating efficiencies can

be obtained with the correct pump design.

IV. IMPACT OF MODERN CONTROL GEAR AND SYSTEM

MANAGEMENT

Modern control gear and system management capabilities, in

collaboration with the new ESPCP design make it possible

to operate CBM/CSG dewatering/artificial lift systems using

compact integrated solutions, ensuring component

compatibility, reliable operation and user friendly operation.

A. Harmonious motor, pump and control system selection

The new pump design, together with the appropriate

control system ensure an optimized system, capable of the

necessary starting torque, high operating efficiencies,

reliable start/stop operation and energy optimized solution,

based on the correct motor control applied over an extended

operating range, including full and partial load conditions.

B. Measuring equipment and telemetry

In CBM/CSG applications it is normally required to

report the amount of water pumped, the gas flow rate.

Additionally the water level needs to controlled, making it

necessary to obtain information on the down hole pressure

and casing pressure. Solutions are offered today that

integrate all the necessary measuring equipment, integrated

in such a way that all the information is readily available.

Figure 12 illustrates such a system offering. Reliable

measurements, accessibility, compatibility and serviceability

is possible without unnecessary capital outlay.

Figure 12 Complete CBM/CSG control system, incorporating control

panel, measuring equipment, telemetry and communication integrated on a

single skid.

Another aspect of the proposed measuring equipment that

may result in significant future advantages is based on the

fact that the proposed systems solution offers a per well

affordable measurement capability of gas and water flow

rates, making the detection of line leakages (in both water

and gas) at early stages possible. Additionally, water (total

dissolved solids – TDS) and gas (methane content or

Wobble index) quality can also be monitored.

V. FIELD EXPERIENCE

Several systems have been installed over the past 2 years,

with the bulk number of installations taking place during the

period March to November 2011. The results to date are

summarized in Appendix 1.

A. Background

The core development (based on several years’ pump

and motor experience) was focused on the close-coupling of

the pump and motor. Laboratory tests confirmed designs.

Production models were fabricated and installed in several

wells with a broad spectrum profile, including production

phase wells and pilot wells.

Complete systems were installed, including control panels,

measuring and telemetry equipment as well as

communication equipment. Data was collected on a

continuous basis to facilitate the evaluation of well, pump

and system performance, thereby eliminating the need to

extract pump for evaluation purposes. This made it possible

to obtain early life cycle performance data from various

pumps.

B. Pump and motor performance

Motor performance did not show any significant

unexpected results. The CBM motor is an improved

(materials and minor construction details) version of a

design that has been used extensively in CBM wells in North

America.

Pump performance results indicate and confirm progressing

cavity pump behavior where non-ideal sandy and solids

conditions prevail. High levels of solids impact observably

on pump performance. To estimate pump life after two

years’ of field installations, continuous speed versus flow (at

constant pressure) performance (where available) was

recorded as a measure of wear. The table below shows the

results. Since pressure loss is the main contributor to

performance failure and since the pump speed can be varied

(continuously) over a 2:1 range a representative life time can

be estimated, based on the assumption that a decrease of

performance of 40% will be equivalent to pump end-of-life.

Table 1 Estimated pump life

Solids content and size will always play a dominant role in

this estimation. Additional, observations have indicated that

some wear characteristics include non-linear wear patterns,

meaning that wear may set in initial but be arrested at a

particular point in time. This may be attributable to wear

caused by particles /solids of a specific size reaching a final

or limiting wear characteristic, once tolerances between

rotor and stator reach levels sufficient to pump particles of

a particular size. This observation does make the present

linearized model conservative and it is conceivable that

longer pump life times may be experienced once sufficient

real time data becomes available.

Another important observation, pertaining to pump

performance, is the increased accumulation of solids in the

rising main/tubing where critical fluid velocities (velocities

capable of ejecting solids at the surface) are not met. Solids

accumulating and increasing in the riser/tubing will impede

pump performance by creating an increasing restriction on

the pump, resulting in reduce performance, not because of

pump wear but because of an external restriction placed on

the pump in the form of an increased outlet pressure

condition.

Assuming a linear wear pattern for the present sample it can

be said that pump life varies between 1.28 years and 9.4

years. These numbers need to be tested over time. In actual

terms, given real time operation, the average run time to date

per pump is approximately 10 -11 thousand hours. This is

the time during which the data was collected and the

projections are based.

The performance results of the new ESPCP development in

the field is positive and indicates a sufficient degree of

success to warrant implementation of the current pump

design.

C. System, data and communication

The value of real time continuous data collection is clear

when considering the results obtained from the field

installations where data was available. Challenges associated

with communication, measurement of multiphase media and

other system characteristics were identified and solutions

implemented. Reliable systems operation and management

was illustrated through the successful operation of two 5-

spot sites, included in the field data presented.

Several installations in North America (USA) produced

positive results in production wells, including shale wells.

Stripper well applications are also envisaged.

REFERENCES

[1] A. Jonker, Exploring ESPCP (Electric Submersible Progressing

Cavity Pumps) as a dewatering method in Coal Bed Methane gas

fields, Internal report, franklin Electric SA, May 2012.

[2] Laboratory tests – ESPCP development, Franklin Electric Inc.

Bluffton Indiana, 2010

[3] Gas Well Deliquification, 2nd Edition, James F. Lea, Henry V.

Nickens, Mike R. Wells, ISBN: 9780750682800, 2008

[4] Halliburton, Coalbed methane principles and practices, 2008,

Halliburton Company.

APPENDIX 1 - FIELD DATA

Well 1 Well 2 Well 3 Well 4 Well 5 Well 6 Well 7 Well 8 Well 9 Well 10 Well 11

Well Type CBM/CSG CBM/CSG CBM/CSG CBM/CSG CBM/CSG CBM/CSG CBM/CSG CBM/CSG CBM/CSG CBM/CSG CBM/CSG

Pump type ESPCP ESPCP ESPCP ESPCP ESPCP ESPCP ESPCP ESPCP ESPCP ESPCP ESPCP

Motor type Submersible CBM Submersible CBM Submersible CBM Submersible CBM Submersible CBM Submersible CBM Submersible CBM Submersible CBM Submersible CBM Submersible CBM Submersible CBM

Cable Permatrail 10 round Flexible 10 round Flexible 10 round Flexible 10 round Flexible 10 round Flexible CBM 10 Flat Flexible CBM 10 Flat Flexible CBM 10 Flat Flexible CBM 10 Flat Flexible CBM 10 Flat Armoured Flat

Rising main/tubing J 55 2" Flexible CBM Lay Flat J 55 2" J 55 2" Bore Quip (synthetic) J55 2" J55 2" J55 2" J55 2" J55 2"

Pressure transducer 4-20mA 4-20mA 4-20mA 4-20mA 4-20mA 4-20mA 4-20mA 4-20mA 4-20mA 4-20mA 4-20mA

Well head Modified Modified Modified Modified Modified 1500psi 1500psi 1500psi 1500psi 1500psi

Gas flow meter DP Pitot DP Pitot DP Pitot DP Pitot DP Pitot DP/Ultrasonic DP/Ultrasonic DP/Ultrasonic DP/Ultrasonic DP/Ultrasonic Ultrasonic

Water flow meter Mag flow Mag flow Mag flow Mag flow Mag flow Mag flow Mag flow Mag flow Mag flow Mag flow Mag flow

Control panel CBM skid mounted CBM skid mounted CBM skid mounted CBM skid mounted CBM skid mounted CBM skid mounted CBM skid mounted CBM skid mounted CBM skid mounted CBM skid mounted CBM skid mounted

VSD 7.5kW 7.5kW 7.5kW 7.5kW 7.5kW 7.5kW 7.5kW 7.5kW 7.5kW 7.5kW 11kW

Controller RTU IP RTU IP RTU IP RTU IP RTU IP RTU IP RTU IP RTU IP RTU IP RTU IP RTU IP

Communication local 2.4GHz 2.4GHz 2.4GHz 2.4GHz 2.4GHz 2.4GHz 2.4GHz 2.4GHz 2.4GHz 2.4GHz

Communication remote GSM GSM GSM GSM GSM Satellite/GSM Satellite/GSM Satellite/GSM Satellite/GSM Satellite/GSM GSM

Water line pressure -operating (bar) <3 <3 <3 <3 <3 <3 <3 <3 <3 <3

Casing pressure max. (bar) <5 <5 <5 <5 <5 <5 <5 <5 <5 <5

Total vertical depth (m) 286 280 274 286 280 490 484 480 490 475 690

Total insertion length (m) 286 280 274 286 280 490 484 480 490 475 800

Angle of pump from vertical (Deg) 0 0 0 0 0 0 0 0 0 0 78

Target flow (bbl/d) 150 150 150 150 150 300 300 300 300 300 74

Actual flow (bbl/d) 160 120 100 75 70 110 80 40 70 270

Water quality TDS ppm <4000 <6000 <4000 <4000 <4000 <3000 <3000 <3000 <3000 <6000

Solids % Low High Low Low Low Low Low Low Very high Low

Solids type Sand Sand & Fines Sand Sand Sand Sand & Fines Sand Sand Sand Sand

Solids size Fine Coarse Fine Fine Fine Fine Fine Fine Coarse Fine

Was a shroud used No No No No No No No No No No Yes

Well construction Close cased Close cased Close cased Close cased Close cased Close cased Close cased Close cased Close cased Close cased

Flow rate/Freq 57 57 39 - 19 - - - - -

Flow rate/Freq (150 days' operation) 55 56 34 - 18.5 - - - - -

Initial install date Mar-11 Oct-10 Mar-11 Mar-11 Mar-11 Nov-11 Nov-11 Nov-11 Nov-11 May-11 Mar-12

Total recorded run time (h) 10658 11894 7810 11795 3670 3710 676 3102

Number of Days in Operation 534 181 535 356 535 157 155 88 158 204

2nd Unit Install date Mar-11 Feb-12 Aug-12 Nov-11

Total recorded run time (h) 9725 -7810 3770

Number of Days in Operation 405 179 36 158 0

Power supply Mains Mains Mains Mains Mains Generator Generator Generator Generator Generator Generator

Comments Running

Severe scaling

present. Pump

replaced Feb 2012.

Pump removed May

2012.

Running.

Running. Pump

replaced with lower

flow rate.

Running.

Running. Casing 101

mm ID - restricted

space. Well shut down

for rehabilitation Mar

2012 - Aug 2012.

Running. Pump

replaced. Casing

101mm ID - restricted

space. Well shut

down for

rehabilitation Mar

2012 - Aug 2012

Abandoned. Casing

101mm ID - restricted

space. Well

abandoned - not

viable.

Running. Casing

101mm ID - restricted

space. Extreme sand

content. Pump

replaced once.

Maximum frequency

reached after 154 days

and coloumn (3 meter

length) filled with

sand. Well shut down

for rehabilitation Mar

2012 - Aug 2012

Running. Casing

101mm ID - restricted

space. Pump and

motor replaced once

due to scaling. Well

shut down for

rehabilitation Mar

2012 - Aug 2012

Pump replaced due to

silting. Flow sleeve

design changed.

Figure 13a Field data. During the operational period in cases where changes were made to pumps or motors data averaging was used to obtain meaningful results. Pump wear information provided was obtained on a continuous basis by

comparing flow rate versus frequency for constant pressure duty points. Pumps were only removed and tested once operational requirements could not be met. In these cases pump tests confirmed loss of performance to below useful duty.

Well 12 Well 13 Well 14 Well 15 Well 16 Well 17 Well 18 Well 19 Well 20 Well 21

Well Type CBM/CSG CBM/CSG CBM/CSG CBM/CSG Shale Shale CBM/CSG CBM/CSG CBM/CSG CBM/CSG

Pump type ESPCP ESPCP ESPCP ESPCP ESPCP ESPCP ESPCP ESPCP ESPCP ESPCP

Motor type Submersible CBM Submersible CBM Submersible CBM Submersible CBM Submersible CBM Submersible CBM Submersible CBM Submersible CBM Submersible CBM Submersible CBM

Cable Armoured Round Armoured Round Armoured Round Armoured Round Armoured Round Armoured Round

Rising main/tubing 2 3/8" EUE 2 3/8" EUE 2 3/8" EUE 2 3/8" EUE 2 3/8" EUE 2 3/8" EUE 2 3/8" EUE 2 3/8" EUE 2 3/8" EUE 2 3/8" EUE

Pressure transducer 4-20mA 4-20mA 4-20mA 4-20mA 4-20mA 4-20mA 4-20mA 4-20mA 4-20mA 4-20mA

Well head

Gas flow meter

Water flow meter

Control panel

VSD

Controller

Communication local

Communication remote

Water line pressure -operating (bar)

Casing pressure max. (bar)

Total vertical depth (m) 146 483 302 335 389

Total insertion length (m) 146 483 302 335 389

Angle of pump from vertical (Deg) 0 0 0 0 0 0 0 0 0 0

Target flow (bbl/d) 150 150 75 300 30-35 30-35 150 75 150 75

Actual flow (bbl/d)

Water quality TDS ppm

Solids % Very High Very High

Solids type Sand Sand

Solids size

Was a shroud used Yes Yes Yes Yes Yes Yes Yes Yes Yes

Well construction

Flow rate/Freq

Flow rate/Freq (150 days' operation)

Initial install date 28-Jun-11 28-Jun-11 29-Jun-11 08-Sep-11 17-Nov-11 09-Jan-12 Jun-11 Jun-11 Jun-11 11-Sep-11

Total recorded run time (h)

Number of Days in Operation 453 453 452 381 311 258 7 7 98 30

2nd Unit Install date Nov-11

Total recorded run time (h)

Number of Days in Operation 16

Power supply

Comments Running Running Running Running Running Running Pump failed - Run Dry

Pump not sized right

for well. Removed to

be placed in another

well

Initial Install - Sand

wore hole in motor

shell

2nd Install - Tubing

broke severing cable.

Shroud filled with

sand around motor

and up to intake of

pump. Still running

OK at time of removal.

High sand content

well. Initial ESP

installed into this well

lasted 7 days.

Figure 13b Field data. During the operational period in cases where changes were made to pumps or motors data averaging was used to obtain meaningful results. Pump wear information provided was obtained on a continuous basis by

comparing flow rate versus frequency for constant pressure duty points. Pumps were only removed and tested once operational requirements could not be met. In these cases pump tests confirmed loss of performance to below useful duty.