SUBSEA WELL INTERVENTION

TECHNOLOGY

Submitted by:

YOHANEST CHANDRA (A0065919R)

OT5301 MECHANICAL ENGINEERING OIL & GAS TECHNOLOGY

DEPARTMENT OF MECHANICAL ENGINEERING

NATIONAL UNVERSITY OF SINGAPORE

February 2010

INTRODUCTION

Over the past few decades, the world has realized of its dependence on petroleum. It has

significant contribution in human daily activities. Mainly, the majority of world's

unexplored oil wealth lies largely offshore. Realizing the direction of oil & gas

technology, many industries have extended its early exploration and production

operations with land-based rigs to exploration of the earth covered by ocean. It was faced

with the deepwater challenges of what is called the "last frontiers" on this planet (the

sea).

Nowadays, oil & gas industry has changed their main focus of development from onshore

to offshore. This evolution from land to sea has occurred over the past century. Offshore

technology applications which have been developed are; offshore platforms,

semisubmersible and jackup drilling rigs, and dynamically positioned drill- ships, FSO,

FPSO and FDPSO. Offshore technologies advanced to conquer increasingly hostile and

challenging environments. From one point on a fixed platform or floating rig, wells could

be drilled in multiple directions to reach more of the reservoir. The latest development of

subsea technology has reach 3,000 m depth from the sea surface. Developing this subsea

prospects in water depths up to 3,000 m really required outstanding engineering skills,

equipment qualification and extreme focus on reliability.

The world markets for the subsea industry was also changing, the need to operate in

developing countries like in West of Africa was essential for long-term success in the

subsea oil and gas business. Many successful subsea industires were forced to relocate

their share of the billions of US$ being invested in subsea projects every year. The

urgency to improve and increase the productivity of the Oil well productions drive many

industries to develop new technology to meet this need and subsea well intervention is

one of its development as the technology is moving towards to offshore.

TABLE OF CONTENT

INTRODUCTION

I. SUBSEA WELL INTERVENTION TECHNOLOGY …………… 1

1. WELL INTERVENTION ……………………….………………... 1

A. WIRELINE OPERATION ………………….…………………. 5

B. COILED TUBING OPERATION ….…………………………. 7

C. HYDRAULIC SNUBBING UNITS …………………………… 8

2. SUBSEA WELL INTERVENTION .…………………………….. 10

A. TYPE OF SUBSEA WELL INTERVENTION .……………… 12

I. LIGHT SUBSEA WELL INTERVENTION …………… 12

II. MEDIUM SUBSEA WELL INTERVENTION ………… 13

III. HEAVY SUBSEA WELL INTERVENTION ………….. 14

3. SUBSEA WELL INTERVENTION IN THE MARKET ………… 15

4. FUTURE DEVELOPMENT ………………………………………. 21

CONCLUSION

REFERENCE

CHAPTER II

SUBSEA WELL INTERVENTION TECHNOLOGY

1. WELL INTERVENTION

A well intervention is also known a 'well work'. It is defined as any operation carried

out on a oil or gas well during, or at the end of its productive life, that alters the state of

the well and or well geometry, provides well diagnostics or manages the production of

the well.[1] This well intervention is carried out to maintain, improve production levels,

repair of wellbore mechanical failures or to suspend production.

There are a lot of problems that are found during the operation of Oil well. These

problems cause the productivity of the oil well to decrease and it drives the industry to

develop a new technology to overcome the problems. Here are some potential problems

that are found in oil well operation:

• Low Reservoir Pressure

The reduction in reservoir pressure and flowrate is particularly acute in dissolved

gas drive reservoirs. In gas cap and water drive reservoirs, pressure maintenance

techniques can often offset the reduction in pressure due to depletion. This

problem can be solved by recomplete the well with either smaller tubing or some

form of artificial lift and injection

• Wellbore Restrictions

Typical causes of restrictions include scale, sand, paraffin and asphalt etc. Many

of these problems may not be apparent during early field life but can become a

significant problem as the field matures.

A number of techniques, both mechanical and chemical are applied to remove the

restriction. However, consideration should always be given to the prevention of

the problems as these techniques are remedial.

• Primary Cement Failures

A poor primary cement job which leaves channels behind the casing can lead to

the influx of unwanted fluids and in certain instances casing collapse. Squezee

cementing has to be done to solve this issue.

• Loss control of water and gas production

Losing control of the water and gas production can cause loss of productivity. A

mechanism to control it is needed to re control the water and gas production

• Mechanical Failures

Mechanical failures of tubing, casing and downhole equipment are often

happened. It requires a workover to rectify the problem. These typical problems

would include: casing leaks, tubing failures, packer failures and downhole safety

valve failures.

Well intervention has its main objective to improve or increase the productivity of the oil

wells. It is estimated that with subsea wells intervention could enhance oil well

productivity by at least more than 25%. This enormous enhancement of the oil well

productivity of course can’t be achieved easily. Well intervention technology has to face

many challenges to obtain its objectives. The main challenge that has to be faced is lack

of commonality of Christmas trees which were used in subsea operation. Each and every

Oil well may have different design of Christmas tree. It makes many industries find

difficulties and have to adjust or modify their well intervention application to fit each of

oil well operations.

There are a lot of well intervention services that has been done such as: Logging, light re-

perforating, plug setting/removal, flowline intervention, well commissioning, well

abandonment, down-hole pump change out, scale cleanout, down-hole valve retrieval,

casing leak repairs, re-drill, etc [lect notes]. Perforating and fishing will be discussed in

detail in below section.

Perforating

Perforating is an operation whereby holes are made though the production casing

ans its cement sheath into the reservoir to permit oil or gas to flow into the

wellbore. Nowadays, bullets perforator is the most common perforator that being

used. Preforation must provide a clean flow channel between the producing

formation and the wellbore with minimum damage to the producing formation.

There are three basic perforating guns type: Retrievable hollow carrier gun, Non

retrievable or expendable gun and Semi-expendable gun. These types of

perforating guns can be used through three standard methods:

• Casing gun perforating – It is run on the wireline operation

• Through Tubing Perforating (TTP) – It is run on wireline operation

• Through Conveyed Perforating (TCP) – It is run on coiled tubing operation

Figure 1: Methods of perforating system

TCP is the most used perforating technique because it combines the best features

of both casing gun and through tubing gun.

TCP method has some of advantages:

• It can perform a large interval perforating in one time

• It is easy to perforate in deviated well

• Large gun can be used with high shot density

• It can be carried out in unbalanced condition

• It is the safest method until now.

Despite of its advantages, TCP has some disadvantages if it fails to be perforated.

It will need to pull out the entire system and and additional hole must be drilled

below the reservoir to accommodate the gun.

The perforating gun is run as integral part of the drill system test or a completion

string. It will be only fired after a packer has been set, a surface tree has been

installed and the entire completion string pressure integrity has been tested. Firing

can be achieved using mechanical system or electrical system. Annulus or tubing

pressure is used for mechanical system. One of the examples of mechanical

perforating system is Hydraulic Time Delay Perforating.

Figure 2: Mechanism of Hydraulic Time Delay Perforating

Fishing

Fish is an object that is left in the wellbore during drilling or workover operations

and that must be recovered before work can proceed. [2]. It can be anything from

a piece of scrap metal, pipe, wireline to a part of the drill stem.

Fishing is defined as any action taken which attempts to remove a fish from

borehole. Fishing tools are designed to engage with items that were not originally

designed to be engaged. It will be specially designed to accommodate the type of

action that needs to be taken. This fishing tool is connected to the wireline

operation to recover equipment lost in a well. There a lot of types of fishing tools

are available in the market.

There two release mechanism for fishing. They are mechanical release system and

hydraulic release system. Most of the operators prefer to use hydraulic release

system. Despite of the preference, the mechanical release system has advantages

over the hydraulic system where in gas wells, which do not support a fluid

column, or in case the introduction of water to the formation has to be minimized.

Some of fishing tools example are:

Figure 3: Mechanical Release system (left) and Hydraulic Release system

The most common techniques utilized to perform well intervention services are

wireline operation, coiled tubing operation and hydraulic snubbing unit.

A. WIRELINE OPERATION Wireline operation is defined as any techniques used to operate in producing and

injecting well by means of a steel cable, to enter, run, set and retrieve

measurement tools and instruments need for production [3]. A lot of services can

be performed using wireline operations: logging, light re-perforating, zone

isolation, plug setting/removal.

Wireline operation is being done using slickline, Braided line or electric line.

Slickline is a solid single strand of wire. The commonest size being used is 0.108

in. Braided line consists of stranded wires resulting in higher load capacity than

slickline. It usually used to perform fishing when slickline is not sufficient to take

the load. Electric line consists of stranded wire and a conductor which capable to

transmit an electric signal to the surface or vice versa. Electric line is used where

electronic application is being utilized in well intervention service such as:

cased-hole formation evaluation, production logging, re-preforating, setting

bridge plugs and packers, etc.

Wireline units are installed on offshore platforms are typically skid mounted. The

wireline is spooled on to a reel that is usually hydraulically driven. To perform

wireline operation, in minimum it requires : wireline, wireline winch unit,

lubricator, measuring device, hay pulley, wireline clamp, stuffing box, weight

indicator and Blowout preventer (BOP).

Figure 4: Open Water Wire Slick line Operation

Wireline operation utilizes many tools which can be categorized into several

types. They are:

• Checking and Maintenance Tools

The tools are screwed directly on the bottom of the wire line. It is used

for checking and cleaning of tubing inside the well. Examples of this tool

are swaging tools, sand bailers, scratchers and gage cutters.

• Running and Pulling

Tools that has been specially designed for pulling or retrieving downhole

tools

• Fishing Tools

Fishing tool is used to remove any undesirable items from the borehole.

Despite of many well intervention services that can be done using wireline

operation, it has some limitation limitation:

• It is risky to be operated in highly deviated wells

• It requires highly skilled personal to operate

• No rotation and circulation are possible for this operation and can only

work in tension and moderate loads.

In overall, wireline operation has the advantages:

• The operation can be done inside the tubing without killing the well.

• Due to light weight and its mobility, the operation can be performed fast.

• No damage to the pay zone during the operation

• Relatively easy to handle

• Not really expensive in cost and many operators are available in the

market

B. COILED TUBING OPERATION Coiled tubing operation serves for bigger size and bigger load than the wire line.

It requires heavier equipments compare to wire line operation. In the application,

usually coiled tubing operation is the operation before wireline operation. It is

always carried out together with wireline operation. This unit operation is usually

carried out for Nitrogen lifting, sand lifting, circulating fluid, fishing, cleaning

out the well bore utilizing a downhole motor.

Figure 5: Example of Coiled tubing technique

C. HYDRAULIC SNUBBING UNITS Snubbing is also known as hydraulic workover. The principle is that pipe

can be inserted or withdrawn from a well under pressure. The process

utilizes jointed tubing or drill pipe with a hydraulic snubbing unit to run

the tubing string without killing the well, and allows small diameter tubing

to be run through the completion. Snubbing unit is heavy equipment and

consists of hydraulic jack assembly, guide tube, window, travelling and

stationary slips, rotary table and power tongs, work basket for control

panel, hydraulic power pack, circulating swivel, kelly hose, pumps and

BOP stack

Snubbing unit should be able to perform three basic functions:

• Feed the pipe into and out of the well in a controlled manner against

wellhead pressure.

• Provide a seal which maintains integrity while at the same time allowing

the pipe to be inserted or removed from the well.

• Provide a means of plugging the inside of the pipe.

Snubbing unit can be used to perform: fishing, milling in casing, cleaning

out cemented solids in the tubing/liner/casing, pressure control/well

killing, drilling out bridge plugs, washover, circulating out heavy fluids,

acidizing, squeeze cementing.

Hydraulic workover units have several advantages:

• It has greater capability than coiled tubing; it can handle relatively large

tools.

• It can be performed under pressure and in certain cases with the well still

flowing.

• Mobilisation and demobilisation are shorter reducing the overall time a

well is off production.

• The ability to rotate the pipe enables light drilling and milling work to be

performed.

Figure 6: Snubbing Unit

2. SUBSEA WELL INTERVENTION Oil and Gas technology has been moving toward an offshore. Economic is the main

driver for this evolution. The growth of subsea technology can be seen in figure below.

Figure 7: Growth of Subsea Technology

Subsea operation has been under performed by 25% compare to onshore operation

because of well intervention [4]. This shortfall in productivity equates to $20.7 million.

Hence, subsea well intervention is being developed to answer this challenge. Subsea well

intervention is just simply well intervention technologies that being carried out offshore.

Subsea well intervention is relatively new technology and the cost of operation is very

high, but it has been predicted will regard promising market in future. Subsea well

intervention requires much advanced planning as it offers up many challenges.

Subsea well intervention is typically assisted with a vessel and sometimes also requires

ROV (Remote Operation Vehicle) to perform its services such as production logging,

stimulation, SCSSV change out, re-perforation, leak tubing repairs, fishing, well

suspension, etc.

Figure 8: Below is the statistic of subsea well intervention has been carried out till 2006

Many industries have been trying to become a pioneer in the implementation of subsea

well intervention.

• Shell and Oceaneering International have claimed that they have set a new

industry record in subsea well intervention by replacing a failed subsurface-

controlled subsurface safety valve in the Gulf of Mexico using an open water

wireline technique at a water depth of 2,673 ft (815 m) [5].

• ATP Oil & Gas and Blue Ocean Technologies also have claimed that they have

set multiple new industry records in subsea well intervention in 2950 ft of water

without a riser. Blue Ocean Technologies' Interchangeable Riserless Intervention

System (IRIS) successfully completed numerous riserless wireline runs,

deploying a variety of intervention tools, including a wireline tractor, gauges,

milling tools, perforating guns, and a logging tool multiple times, each run of

which represents a new industry record for riserless intervention. This is the first

time that wireline has been successfully run in open water at 2950-ft depth. [6]

A. TYPES OF SUBSEA WELL INTERVENTION Based on the types of vessel which accommodate the well intervention operation,

it classified into three major classifications: Light, Medium and Heavy subsea

well intervention.

Figure 9: Types of Subsea Well Intervention

I. LIGHT SUBSEA WELL INTERVENTION

Light subsea well intervention is a subsea well intervention which

required only small vessel as its marine support vessel. The operation

that able to be performed is a wire line operation. Light subsea well

intervention can performed service limited to logging, light perforating,

zone isolation plug setting and plug removal.

Light subsea well intervention operation is usually carried out in 9 days/

well job and costs around $150K to $200K/day of operation [4]

Figure 10: Light subsea well intervention

II. MEDIUM SUBSEA WELL INTERVENTION

Medium subsea well intervention is defined as any operation in a subsea

wellbore that does not need a drilling rig to gain access to the well to

convey the service or to carry out the operation [7].

Medium subsea well intervention is actually almost similar to light

subsea well intervention. The difference is that medium subsea well

intervention employs coiled tubing together with wireline operation.

Hence, heavier task can be carried out. Medium subsea well intervention

can perform flowline intervention, well commissioning, perforating, well

abandonment, downhole pump change out, squeeze, acidizing , water

shut-off, scrapping, valve retrieval, casing repair, etc. Medium subsea

well intervention has wide scope of service but it still has its limitation

which it only can perform operation which not required any drilling rig.

This type of operation will require heavy subsea well intervention.

Medium subsea well intervention operation is usually carried out in 9

days/ well job and costs around $150K to $300K/day of operation [4].

Figure 11: Medium subsea well intervention

III. HEAVY SUBSEA WELL INTERVENTION

As it shows from the name, heavy subsea well intervention will involve a

lot of heavy equipment such as drilling rig with all heavy equipment on

top of it. Multiple service companies can be rigged up and working from

this stable platform. A lot of heavy services can be performed by heavy

subsea well intervention such as: scale milling, completion of change out

or repair, re-drill, sidetrack and Christmas tree change-out.

Heavy subsea well intervention operation is usually carried out in 9 days/

well job and costs around $360K to $840K/day of operation [4].

Figure 12: Heavy subsea well intervention

3. SUBSEA WELL INTERVENTION SERVICES IN THE

MARKET There a lot of subsea well intervention product in the market. The latest developments

are Risereless Light Well Intervention and Rigless Well Intervention.

RLWI technology was developed in demand of maintaining subsea wells as it can

improve recovery rates and reducing the cost of maintenance. Dynamically

positioned (DP) vessel are used in RLWI to improve the performance of

maintenance and it can be performed more efficient and at lower cost. [8]

Figure 13: Riserless Light Well Intervention

Detail of Rigless Well intervention will be discussed below.

RIGLESS SUBSEA WELL INTERVENTION Rigless subsea intervention system has optimized the capability of two

complementary subsea intervention operation: Wireline Operation and the

Coiled Tubing Operation [9]. It enables rigless coiled tubing, electric line

and slickline thru-tuibing services in subsea wells in water depths of up to

3,000m. The system consists of the subsea Well Intervention Package

(WIP), Intervention Package Control System (IPCS), umbilical, well

servicing equipment, marine support, vessel, handling and deployment

equipment, and ROVs.

Subsea Well Intervention Package

This product from Schlumberger is designed to 10,000 psi and 7 3/8-in

ID size to allow retrieval of larger horizontal tree. The WIP can be

operated using wireline operation or coiled tubing operation [9]. It

consists of three main components:

1. The Lower Intervention Package (LIP)

The LIP has its job to provide a connection of the Well Intervention

Package onto the subsea tree and to provide the required static,

redundant well control barriers

2. The Lubricator Package (LUB)

The lubricator is 7 3/8-in ID in size and has its function to allow the

insertion of toolstrings into the well.

3. The Upper Intervention Package (UIP)

The UIP provides the dynamic sealing function required during in-

hole operations under pressure as well as the capability to safely

disconnect in case of vessel positioning or other emergency problem.

This package is designed to be deployed in a single run for efficient

deployment in deepwater, whenever adequate handling and lifting

facilities are provided on the support vessel. This UIP package is the

one that make the difference between rigless wireline operation and

rigless coiled tubing operation. In coiled tubing operation, UIP

package incorporates a subsea dynamic seal. This seal is the well

control barrier and features a dual redundant sealing element package

that deployed and retrieved with tool string on every run. Whereas,

UIP package in wireline operation is based on existing stuffing box

technology to seal against slickline. A polymer embedded cable has

been incorporated so that can be used as if it is slickline for sealing

purposes. UIP wireline operation package has the advantages over

the UIP coiled tubing operation package. Its cable is combined with

the seal and eliminates grease injection for operation.

Figure 14: Main component of Well Intervention Package

Intervention Package Control System (IPCS)

IPCS is the main controller of the rigless well intervention. It has main

functions of the control system to:

• remotely actuate the WIP and a configurable array of subsea

Christmas tree functions from the vessel

• enable a subset of WIP and subsea tree functions using the ROV

• acquire various WIP data in real time for transmission and display at

surface

• automatically or manually initiate a sequence of WIP functions in

case of emergency

The control system architecture of IPCS is common for both wireline

operation and coiled tubing operation. The control system is based on

a distributed system architecture where independent valve modules are

installed at various locations on the WIP. Electronics control is

installed near the valves which are to be operated in identical fashion

as the control systems used on most modern work-class ROVs. The

control system also provides power and controls to a dual redundant

subsea WIP Pumping System which mounted on the LIP to provide

the required pressure testing, lubricator flushing and hydrate

prevention / remediation functions.

Umbilical

The umbilical is comprised of two separate power and communication

bundles, one for each multiplexed telemetry system (operating and

stand-by). Launch and Recovery System (LARS) is used on the side of

the vessel to deploy the umbilical for ease and can be actively

positioned from surface to facilitate down-line management.

Well Servicing Equipment

Standard slickline, electric line, and coiled tubing equipment packages

can be used with this system. Some synergies are gained through cross

training of personnel and co-location of power and control features.

Marine Support

Marine support is a vessel which assists the WIP operation. The WIP

package can not be deployed anytime we want it. It will depend on the

nature condition such as wave height and current of the sea. It is the

reason marine support is needed. Based on the size of equipment and

also operation, marine support vessel has some requirement:

• 100 to 120m length by 20 to 25 m breadth

• Minimum 1,000 m² deck space, excluding ROV requirements. Some

equipment such as pumping units and liquid storage tanks will be

integrated into the hull of the vessel

• Dynamic position level 2

• Living quarters for minimum +/-95 personnel

• Two 150 hp Work Class ROVs

• 7m x 7m moonpool

• Handling tower or mast with AHC deep water winch or AHC deep

water crane

It should be noted that for wireline service has smaller deck space

requirements, the vessel could theoretically be smaller

Handling and Deployment Equipment

The handling system consists of the following main components:

• Tower to support the well intervention package components as they

are prepared to be run into the water column and through the splash

zone. This includes a cursor system to guide components through the

splash zone and means of opening / closing the moonpool.

• Deployment Winch to lower and retrieve the well intervention

package components to and from the seabed

• Hang-off system for the support of the well intervention package

components at the level of the moonpool door

• Skidding System to move equipments on the support vessel from

parking positions to working and/or deployment positions

• Umbilical Handling to launch and recover the control system

umbilical.

• Tensioner to deploy the coiled tubing through the water column

ROVs

Two ROVs are required for redundancy. The ROVs are work-class

ROV’s with a power of about 150 hp and rated for a maximum

water depth of 3,000 m

On the objective to bring the Rigless subsea intervention services to

3000m, some challenges are found. These challenges are:

• No Guideline

Guideline-less deployment is only relying on the ROV and marine vessel

support for positioning and guiding the package on to the subsea tree. The

lack of guidelines calls for an active heave compensation system. Two such

AHC systems for electric line logging are currently being trialed.

• Umbilical Size

Bigger size of umbilical has bigger diameter of umbilical cores. It will lead

to friction losses versus water depth reach its practical limits of non-metallic

hose technology. When the size is bigger, he weight of umbilical is also

become bigger and it will come to the hydraulic umbilical become

impractical. Of course placement of Hydraulic power unit and pumping

system subsea can eliminate this issue, but it would be expensive.

• Hydrate at dynamic seal

There is a potential of hydrate formation in dynamic seals made from

polymer encapsulated cable (marinzed version) when the gas enter the

column

• Economic availability

Rigless subsea intervention is as much of a commercial exercise as it is a

technical one. If the rigless intervention system does not result in a

significant reduction in intervention cost then interventions will either not be

performed or will be done using a rig as the basis for

The combination of OWWL and SCG methodologies in a single system

provides a complete and robust LWI solution for rigless subsea

intervention in deepwater. The system excludes welltest operations, but

enables coiled tubing, electric line and slickline operations, and can

complete greater than 80% of the anticipated interventions that do not

entail pulling the completion. The ability to select slickline, electric line

and/or coiled tubing conveyance at will creates a service that as a whole is

greater than the sum of its parts and will be universally applicable. The

cost of intervention is projected to be less than of that when performing

the same intervention with a drilling rig. Multiple conveyance offerings

maximize the chance to successfully complete an intervention by

increasing the possibility to use a variety of tools. A wellbore maintained

subsea results in an acceptable Tolerance of Risk and allows the use of a

cost effective construction vessel to support coiled tubing operations

rather than a drilling rig or large MODU class vessel [9].

4. FUTURE DEVELOPMENT Subsea well intervention technology is considered a new technology in oil and gas

industry. With the driver to move toward offshore technology, it is predicted that new

subsea technology will be improved and may be new invention will arise. Some industry

players have begun to develop various breakthrough and advancement to optimize the

performance of subsea technology. This improvement is moving toward an effective and

efficient subsea well intervention.

CONCLUSSION

Subsea well intervention basically is not much different with onshore well intervention.

Almost all well intervention service that can be done in onshore now can be done in

offshore because of this subsea well intervention technology. The oil and gas industry

demand which want to move the technology towards offshore is the main driver for

subsea well intervention.

Many types of subsea well intervention can be chosen with regards of techniques and

type of vessels support. Base on the techniques, the main of subsea well intervention can

be classified into: Wireline Operation, Coiled Tubing Operation, and Hydraulic Snubing

Operation for heavy duty. Subsea well intervention also can be classified into Light

Subsea Well Intervention, Medium Subsea Well Intervention and Heavy Subsea Well

Intervention.

Subsea well intervention has increased the productivity of the subsea well by around

25%. It has answered the challenged for the improvement of the subsea well but still al ot

of challenge are waiting out there. Subsea well intervention is relatively new technology

and the cost of operation is very high, but it has been predicted will regard promising

market in future. Subsea well intervention requires much advanced planning as it offers

up many challenges. It is predicted that new subsea technology will be developed. More

effective and efficient of subsea well technology will be invented. It is now our call to try

and give our best toward this subsea technology

REFERENCES

[1] http://en.wikipedia.org/wiki/Well_intervention

[2] http://www.osha.gov/SLTC/etools/oilandgas/glossary_of_terms/glossary_of_terms_f.html

[3] Abalt Solution Limited, Well Intervention and Workovers, 2005

[4] Schlumberger, Subsea Well Intervention, 2006

[5] http://www.offshore-mag.com/index/article-display/9023750908/articles/offshore/subsea/us-gulf-of-mexico/2009/12/shell_-oceaneering.html

[6] http://www.worldoil.com/Blue_Ocean_ATP_set_subsea_well_intervention_records.html

[7] Deepstar report, 2002

[8] http://aberdeen.spe.org/images/aberdeen/setup%20Jensen,%20StaoilHydro.pdf

[9] Bill Sierdorfer, Rigless Subsea Intervention: A Nove System Enabling Deepwater Coiled Tubing, Electric Line, and Slickline Operations

OTHER REFERENCES

OT5301 Subsea Systems Engineering Lecture Notes. 2010

http://www.weatherford.com

http://www.slb.com

http://www.fmcthecnologies.com

http://www. spe.org