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Presented atElectrical Submersible Pump Workshop

Houston, TX. USA.

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Recent Advances in Coiled Tubing Deployed ESPs

Juan J. Tovar D. and Craig McK Webster, Innovative Engineering Systems Ltd.

Jeff Dwiggins and Steve Conner, Wood Group ESP Inc.

Abstract

This paper presents recent developments in Coiled Tubing (CT) completion systems using standard and

inverted configurations of ESPs with an internal power cable. In the past, various systems utilised

modified well intervention equipment as surface and subsurface components for CT / ESP completions.

All existing installations with power cable inside the CT string also utilise inverted pumps. Invertedpumps were developed to be used with the Cable Deployed Pumping System

(1). Due to the inherent

design limitations and field problems encountered(2,3,4)

with this type of system an alternative approach

was taken to design new systems that take full advantage of CT technology. Recent developments

include purpose designed and built surface and subsurface assemblies, including a production spool

featuring a non-enclosed type hanger without lock down screws. A non-permanent, non-damaging cable

suspension system has also been developed. Suspension is based on a friction concept and is provided in

such a manner that cable movement is permitted (but minimised) and no damage or indentation is

caused to the CT either internally or externally. The subsurface components allow integration of

conventional or inverted pump assemblies and the CT / cable assembly. This paper describes in detail

the new systems and their components.

Background

Alternative deployed ESP's have been a developing technology since the early 1970s (5). One of the first

systems to be developed commercially utilised a strength bearing cable that was banded to the ESP

power cable(1)

. Problems encountered in using this system involved the banding of the two cables, and

the rotational characteristics of the strength bearing cable. The second of these problems was overcome

by using a torque-balanced cable. Although the system could be run without the use of a drilling or

workover rig, greatly reducing cost of installation / retrieval. A dedicated winch unit was required to

deploy the completion. CDPS*continues to be used on a limited basis

(6).

In the early 90s further developments led to the deployment of ESPs with Coiled Tubing still using the

power cable outside the CT (7). In 1995 the first CT deployed systems were installed placing the power

cable inside the CT string.(2,8)

The major benefits of locating the power cable inside the CT are a

reduction in operational time and the ability to deploy the completion under live well conditions,

avoiding costly well killing operations and productivity impairment. Experience gained with the first

prototypes proved the feasibility of the concept and indicated that significant timesavings could be

realised. However, various events highlighted the need for further development. Packer discharge head

failure and relative short run life of the installation were clear indications of potential problems.

Premature commercialisation of the technology confirmed these problems during the first installations,

*CDPS is a trademark of Schlumberger

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where the operator reported cable slippage and installation failure (3). Further improvements have to

some extent solved these problems. Most of these systems utilised CDPS technology that includessacrificial tubing with a nipple located at a pre-determined depth where the pump is to be set. Table 1

presents the main characteristics of the currently available systems.

Other pump manufacturers have made significant progress towards developing alternative systems (9),

making a particular effort on cable suspension mechanisms and subsurface systems functionality such as

packer discharge heads, release systems.

Internal Cable Suspension

Several methods for suspending cable have been developed since the two-cable system. The firstsystems utilised a small clamp that is attached to the power cable

(2,8). The cable and clamps were then

pulled through the Coiled Tubing using wireline or a smaller diameter tubing. The clamps were

activated when the CT was pressurised. Within the clamp, the upper section of a cylinder surrounding a

piston extended outward against the wall of the tubing, indenting the CT and fixing the clamp and the

suspended cable in place. Another system was developed in the late 90s that suspends the cable by

indenting the CT around a spacer that is attached to the cable (9)

. The connection mechanism is

analogous to that of a Dimple-On CT connector in which a number of external indentations are made

throughout the string length.

A disadvantage of both the above systems is that they involve deformation of the Coiled Tubing to some

extent. As the working limits of the tubing are already being maximised, such damage can reduce thenumber of safe working cycles for the string. Independent testing has been carried out to evaluate the

level of damage caused by the indentation process (4). Figure 1 illustrates indentation of the internal

walls of the CT caused by a suspension system. Field results indicate that both systems have worked

with varied rates of success.

One of the most common concepts that can be used in supporting the cable is buoyancy. Difference of

opinion still exists as to the loading that cables can support. Thus, there is a point at which the power

cable will fail mechanically under its own weight. Using buoyancy as means to suspend cable implies

that the weight of a submerged cable is reduced according to levels where no plastic deformation takes

place in the conductors. The buoyancy force considers the particular fluid and cable to be used and can

be calculated using the following equation:

Fb= g x8fx VcWhere:

Fb= Buoyancy Force

= Density of the supporting fluid

V c = Volume of the cable

g = Gravitational Acceleration Constant

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Using this concept, high-density fluid such as solids laden muds can aid in the partial or total suspension

of the cable. Although effective in supporting the power cable, it is restricted because of the nature ofthe suspension fluid. High-density mud has a tendency to segregate with the heavier particles settling

out. Should high-density brines be considered, a cost element needs to be accounted for. In addition to

this, the added weight of the fluid to the CT / Cable assembly can in some cases increase the running

and pulling loads to unacceptable limits. Furthermore circulation of fluids through the CT string cannot

be achieved as introducing a lighter fluid into the annulus results in a lower buoyancy force that may

cause cable failure. While the technical arguments continue, there is no doubt that for certain type of

wells cable suspension might not be required. However, that is not always the case and each particular

scenario needs to be analysed on its own merits. Figure 2 illustrates typical cable loading with and

without buoyancy for an application in the North Sea.

The concept of CT deployed ESPs with an internal cable assembly is a viable and cost effectivealternative despite the various technical problems encountered to date that have clouded its true

potential. The problems encountered are the result of limited engineering, testing and premature

commercialisation. Most of the concepts available in the industry work but could be significantly

improved. The opportunity to take full advantage of the cost and technical advantages of the technology

is still un-exploited. The following paragraphs present the development of a Reeled Electro-Submersible

Lifting Completion System - ReELIFT*for both conventional and inverted pump systems.

Completion Philosophy

The requirement for a CT deployed ESP completion system is aimed mainly at the economics, reliabilityand safety aspects. Following the industry demand for optimised economics through better use of

technology, development of such a system has to be based on the following premises:

Operational viability and cost.

Integration of field proven technology.

Live well installation and retrieval.

Well barriers and safety philosophy

Rig-less deployment and retrieval

The economic implications of using this technology in high cost environments such as the North Sea

have been assessed before (11). Based on the previous experience and the previous premises a completion

system was developed and is presented in the following paragraphs.

*ReELIFT is a registered mark of Innovative Engineering Systems Limited

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Surface Assembly

An innovative surface assembly based on a new hanger, production spool and bonnet type has been

designed to increase the efficiency of running and retrieving the completion. The surface assembly is

common to both types of ESP completion (i.e. conventional or inverted pump) The most noticeable

difference between this system and more conventional designs is that there are no tie-down bolts.

Instead the hanger is locked in place by dogs, which locate inside the spool. When the running tool is

locked into the hanger, it activates a collar that allows the hanger's landing and release from the spool.

As the running tool is retrieved, the locking collar is pushed up by a spring, forcing the dogs to lock into

the spool body. An indicator pin stands out of the spool body until the hanger has been fully locked into

position. This also doubles as a leak detector. Should the seal systems between the hanger and the spool

body fail, the increase pressure will push out the indicator pin warning of lost seal integrity.

A conventional wellhead penetrator is passed up through the bonnet, and locked in place by a retaining

nut. Figure 3 illustrates the surface assembly in more detail. Additional features of the design include a

barrier between the CT and the hanger ensuring well isolation via the internals of the CT/Cable

assembly. Other options to the surface assembly include production wing outlets mounted on the spool.

Cable Suspension

An innovative cable suspension system was developed based on friction. One of the main concerns in its

development was for the cable suspension mechanism to reduce the risk of string failure due to internal

or external damage caused to the CT as with the current systems. As a result, a non-indenting type ofmechanism was developed and extensively tested which allows cable suspension without causing

mechanical damage to the CT. Variable Suspension Units - VSU* are attached to the cable and

significantly increase controllable friction between the units and the walls of the CT. Initial prototype

testing was carried out in a test well successfully. An AWG No.1 cable was equipped with cable

suspension devices and deployed into the well. An electronic load recording device was used to monitor

the load variations as the cable was lowered / pulled in the well. At least 15 different configurations

were successfully tried to validate the concept and select the optimum characteristics for maximum

suspension. Further trials were carried out using stainless steel as requested by an operator. As a result,

the system can be configured to provide optimum cable suspension for conventional A 606 alloys or

Super Duplex steels that have recently being introduced to the CT market. Figure 4 shows an early

prototype being lowered in the test well. The developed system has the following features:

Non damaging to the CT

Simple installation and retrieval

Suspension with or without buoyancy

Suitable for A606 or Super Duplex CT

The suspension unitshave non-moving parts that make manufacturing, installation and activation more

simple and cost effective. Continuing developments include features that will allow safe cable retrieval,

*VSU is a registered trademark of innovative Engineering Systems Limited

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making the technology more cost effective in the years to come. Evolution of the cable suspension units

is shown in Figure 5.

Sub-Surface Assembly Conventional Pump

The most common configuration for CT deployed ESPs is the inverted pump assembly. The main

reason for utilising this configuration is that by placing the motor above the pump, the cable can be

connected directly onto the motor head housing. This eliminates the requirement for an MLE (motor

lead extension) from the head of the pump to the pothead on the motor. These features are original in the

CDPS system but CT has replaced the strength member, retaining the same pump configuration and

system limitations. The main disadvantage of this configuration is that it requires sacrificial tubing,

imposing a fixed pump setting depth giving limited flexibility. Inverted pumps are still perceived as new

technology, and continuous reliability problems with the system, inn particular the discharge head hasmarred the perception of the technology.

In providing a BHA that allows a conventional pump assembly to be utilised, several new components

had to be designed. The function of these components is to pass the insulated cable conductors from the

base of the CT string through the packer and into the annulus and to the motor. At the same time the

components had to isolate the conductors from the produced fluids. This was achieved by developing

interfaces that ensure as much as possible the protection of the power cable while providing an effective

flow path. A robust and tested design removed the sealing problem previously encountered using "O"

rings that had led to premature cable failures. The subsurface assembly that incorporates conventional

pumps has the following main features:

Allows well circulation at depth

Safety and reliability by allowing timely release from the packer if required

Integrate a flow control function

Avoid fluid recirculation

Safely isolate the reservoir from potential damage from flow back.

In addition to this, a unique release system has been developed. This allows the well to be circulated

with fluids as required without releasing. To release from the BHA, fluids must be pumped through the

release tool until it is positioned for release. Straight pull will free the CT from the subsurface assembly

and cut the cable leaving a clean fish for further retrieval. This feature allows circulation of fluids up to

the top of the pump as many times as may be required. Release is not affected by circulation henceremoving the problem associated with multiple function subs of this type. Figure 6 illustrates the

circulating and release system.

A Flow Isolation and Control Device is situated at the base of the ReELIFT completion system. It is a

valve that is locked opened by flow. Extensive testing has been carried out to calibrate the flow rate to

lock open the valve. The current design requires approximately 50 gpm to lock the device open.

Pressurising a control line closes the valve. This is to be done when the ESP has been stopped. The

hydrostatic column above the valve energises the Teflon seal on the valve seat. Figure 7 shows most of

the main components of the subsurface assembly.

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The general rule in the industry is the fewer splices / connectors the better. As a result, only one splice

downhole above the ESP motor (MLE splice) is used. The electrical termination at the bottom of the CTutilises a centre tandem lead connector that is a bolt together connection. Figures 8 and 9 show the

electrical connectors on both pieces and the insulators. This connection will take the place of a wet

mateable field type connection reducing equipment cost and improving reliability.

The connection will allow the components to be assembled and tested in a clean environment, and then

taken to the field. The system may also be tested in the shop, insuring a clean and safe assembly. Thewhole unit can then be shipped to site for immediate installation.

Sub-Surface Assembly Inverted Pump

Although the inverted pump configuration lacks some of the advantages of the conventional system, it is

still a cost effective means of artificial lift were an ESP is required. The main advantages are:

No MLE connection is required.

Direct connection of the cable to the motor.

Easy deployment no packer requirement.

However, its limitations and the requirement for sacrificial tubing and a fixed setting depth. In order to

overcome these problems, a packer discharge head has been developed which allows multiple setting

and re-setting of the pump at various depths.

The ReELIFT Series I completion system is designed to be run with an inverted pump. The motor

and seal section is placed above a single component of the system, a packer type component that also

allows discharge of the fluids into the annulus.

The packer is set and unset by a hydraulic control line that can either be run to surface or using fluids

within the CT. There is no requirement for hydrostatic pressure to be maintained during normal

operations. The design provides lock both rotationally and laterally within the casing string and will

hold high pressures from above. The system having many of the features of a conventional packer will

not drag in the well as can be a problem with bag type and similar systems. As the system is over 24

long, a bearing is included for the motor shaft, however further developments are aimed at removing thislimitation.

The flow control device and release mechanism used in the conventional system can also be

incorporated in this assembly. Figure 10 presents the subsurface assembly using inverted pumps.

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Manufacturing and Testing

Two completion systems using conventional pump configurations have been manufactured, tested,

certified and delivered to the Wood Group ESP Inc. They are to be installed during the second quarter of

this year. A thorough testing and certification program witnessed by certifying authorities was

completed. Testing included individual component and assembly integrity tests as well as function

testing. The flow isolation and control device was tested to rates in excess of 12,000 BFPD. The sealing

systems for cable isolation were tested in 6 sections and were able to sustain a differential pressure of

4000 psi when heated to 300F. Other components were tested to 5000 psi differential pressure. The

project was completed 5 weeks ahead of schedule. Figure 11 shows the two systems prior to shipping.

Conclusions and Recommendations

Utilisation of CT deployed ESP technology with the power cable located inside the CT string is reaching

a technically mature age and can provide a cost effective lift option.

Slow implementation to date has been mainly due to the poor field record and lack of technical

alternatives. Both problems are indications of premature release of a technology to the market.

At least four (4) cable suspension devices are available in the market. An Innovative, non-indenting type

avoids internal or external mechanical damage to the CT walls minimising the risk of string failure.

This new design of suspension system has been successfully tested with conventional A 606 alloys andnew super duplex CT materials.

Conventional pump configurations can now be utilised for CT ESP completions. As a result, the

requirement for the installation of costly and time consuming accessories (tubing, packers etc.)

associated with existing inverted pump configurations are no longer needed opening new options to

potential users.

A new completion system (ReELIFT) integrates field proven technology in the design of its surface

equipment, cable suspension and subsurface assemblies. New and improved sealing technology as well

as well safety systems increase reliability and functionality of the system avoiding common problems

encountered with existing installations.

ReELIFT Series I equipment for inverted pump configurations removes all the limitations imposed

by the older technology based on the CDPS units. The completion can be installed without sacrificial

tubing or fixed setting depth.

Series C equipment accommodates conventional pumping technology, improving reliability and choice

for a particular application.

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Acknowledgements

The authors wish to thank Innovative Engineering Systems and the Wood Group ESP for permission to

publish this paper. We are grateful to J. Patterson at ARCO for his sincere contribution to the

manufacturing and testing program, Dr M. McHugh at Lawrence Technology for his comments on cable

suspension and P. McCurdy at IESLfor his efforts in the development of the cable suspension system.

References

1. Reda Pump Company Cable Deployed Pumping Systems, Brochure, Bartesville, Oklahoma, USA.

2. Tovar J. et al, First Field Installation of a Coiled Tubing Powered Electrical Submersible Pump Completion, SPE

paper 28914, presented at the European Petroleum Conference in London, England, October 1994.

3. Hightower C. H., ARCO Drilling and Completion Experience with Coiled Tubing presentation carried out at JNOC-

TRC Workshop on Reeled Tubing Systems, Tokyo, Japan, May 1997.

4. RTD Services Examination of Indentation Depth left by an Internal Cable Support Internal Report 1996.

5. Dwiggins J. and Willard L., Two Cable Deployed Pumping Systems, SPE Workshop, Houston, USA, April 1991.

6. Dublanko G. The Utilisation of a Cable Deployed Pumping System Gulf of Suez, Egypt, SPE Electrical

Submersible Pump Workshop, Houston, Texas, April 1995.

7. Coburn S. et al, Coiled Tubing Deployed Electrical Submersible Pumping Systems, paper 7322, presented at the

OTC, Houston, Texas, USA, 1993.

8. Tovar J. and Head P., ESP Development on Coiled tubing w. Internal Power Cable Technical and Economic

Considerations, presented at the 3rdInternational Conference on Coiled Tubing Operations, Houston, Texas, USA,

March 1995.

9. Centrilift Press Release, Electro-coil on inside track, Press and Journal, Offshore Journal Supplement, Aberdeen,

U.K., 1998.

10. European Patent Application EP 0 899 421 A2 Method of suspending an electrical submersible pump within a

wellbore Filed 25thof February 1998.

11. Tovar J. and Callander J., The Economics of Coiled Tubing Deployed ESP Completions in the North Sea. A Field

Lifecycle Perspective, SPE Paper 35566 presented at EPOC, Stavanger, Norway, 1996.

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Characteristic REDA Centrilift IESL ESP Inc.Sacrificial Tubing Yes - No No

Type of Pump Inverted InvertedConventional &

Inverted

Conventional &

Inverted

Packer Discharge Head Discharge HeadConventional /

Discharge Head

Conventional /

Discharge Head

Surface

SpoolNone None Yes -

No of Connectors 2 connectors -1 connector

1 splice-

Cable SuspensionFixed Anchors

& Friction

Swelling & Fixed

ClampFriction Based Friction Based

CT Damage Indentation Indentation None None

Emergency Release Yes - Yes Yes

Circulation Yes - Yes Yes

Flow Control External - Yes Yes

Number of Wells 8* 1 1** 2**

* 5 more at planning phase

** At planning phase

Table 1 General Characteristics of CT/ESPs

Figure 1 Indentation on Coiled Tubing

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Figure 2 Cable Loading Graph

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Depth (ft)

SurfaceLoad(lbs)

0

7

14

21

28

35

42

49

56

63

WellInclination(deg)

Supported

cable case 1

C ABLE DATA

AW G Round No.1

W eight = 1.77 lb /ft

W ell Inclination Unsupported cable

Supported cable

case 2

M ax Allow ed Load

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Item Description1 Bonnet

2 Spool Body

3 Hanger

4 Indicator Pin

5 Cable Sealing Unit

Figure 3 Surface Assembly

Figure 4 VSU Prototype

Figure 5 - Evolution of the VSU

1

2

5

4

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Figure 6 Circulation / Release Sub

Item Description

1 Coiled Tubing

2 Circulation & Release3 Discharge Head

4 Packer

5 Control Line

6 ESP Cable Conductors

7 MLE Splice

8 Control Line

9 Hydraulic Control Line

10 Flow Control Device

11 Pump & Motor Assm.

Figure 7 Conventional Assembly

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Figure 8 Electrical Connectors

Figure 9 Electrical Connectors

Item Description

1 Coiled Tubing

2 Circulation & Release

3 Control Line

4 Packer Discharge Head

Figure 10 Inverted Assembly

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Figure 11 ReELIFT Ready for Shipping

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