Assigment

SUBSEA UMBILICAL, RISER FLOWLINE

INSTALLATION

Submitted by:

YOHANEST CHANDRA (A0065919R)

OT 5304 – SUBSEA CONSTRUCTION AND OPERATIONAL SUPPORT

DEPARTMENT OF MECHANICAL ENGINEERING

NATIONAL UNVERSITY OF SINGAPORE October 2012

  2  

TABLE OF CONTENT

1 INTRODUCTION ………………………………………………………….. 3

2 UMBILICAL ……………………………………………………………….. 4

2.1 TYPE OF UMBILICAL ………………………………………………. 4

2.2 INSTALLATION METHOD …………………………………………. 6

3 RISER ……………………………………………………………………….. 7

3.1 TYPE OF RISER ……………………………………………………… 7

3.1.1 COUPLED RISER …………………………………………….. 7

3.1.2 UN-COUPLED RISER ………………………………………... 10

4 FLOWLINE ………………………………………………………………… 13

4.1 TYPE OF FLOWLINE ……………………………………………….. 13

4.2 FLOWLINE INSTALLATION METHOD …………………………. 14

4.2.1 TOWING METHOD ………………………………………….. 15

4.2.1.1 BOTTOM TOW METHOD ………………………… 17

4.2.1.2 OFF-BOTTOM TOWING METHOD ……………… 19

4.2.1.3 CONTROLED DEPTH TOWING METHOD ……… 21

4.2.1.4 CATENARY TOWING METHOD …………………. 22

4.2.1.5 SURFACE TOW METHOD ………………………… 23

4.2.2 S-LAY METHOD ……………………………………………… 24

4.2.3 J-LAY METHOD ……………………………………………… 27

4.2.4 REEL-LAY METHOD ………………………………………… 29

4.3 EVALUATION OF SURF INSTALLATION METHOD …………… 32

4.4 OFFSHORE VESSEL SELECTION …………………………………. 35

CONCLUSION …………………………………………………………………... 36

REFFERENCES …………………………………………………………………. 37

  3  

SUBSEA UMBILICAL-RISER-FLOWLINE (SURF)

INSTALLATION METHOD

1 INTRODUCTION

Under-water facilities for oil and gas production are generally referred to using a

subsea prefix. Subsea umbilical’s, risers, and flowline is often abbreviated as

“SURF”. SURF is hardware elements that are required to connect the subsea

systems to top- side systems of a floating production unit. Umbilical, flow-line

and riser installation operations are an essential part of subsea construction.

Compared with fixed platform solutions, development solutions applying floaters

and or SURF solutions will be increasingly important. There will be a doubling

of the offshore oil service market from 2010 to 2016 and offshore E&P spending

will reach US$ 1 trillion in 2030. Today, development solutions containing

floaters and SURF (subsea) covers roughly 40% of offshore field developments –

increasing to 60% in 2030 when tie-backs will drive growth in the subsea market

by 4 times in the period 2012–2030. [1] The below graph shows some major

trends in the development of offshore oil and gas fields.

  4  

Figure 1: Major trend in the development of offshore oil and gas fields. [1]

There are various installation methods and techniques in common use in the

subsea industry and each method has advantages and disadvantages. A subsea

engineer has to ale to provide the best technical solution to the client that is best

suits the specific project.

2 UMBILICAL

Subsea umbilical is basically a pipe connecting subsea wells to surface structures.

It may contain electrical conduits, other pipes, and so on. It is used to operate and

maintain subsea wells or other subsea equipment. Umbilical is also used for gas

lift operation, chemical injection and annulus bleeds.

2.1 TYPE OF UMBILICAL

There are typically 2 types of umbilical. They are static and dynamic

umbilical. The static umbilical has to be designed to be stable on the seabed.

It means there is enough ballast to ensure the umbilical does not move

  5  

around. The dynamic umbilical shall have the capability to withstand

dynamic tension and bending load.

There are a lot of umbilical available in the market. Some of them are:

• Steel Tube Umbilical

The main considerations for steel tubes in umbilical service are

tensile strength, corrosion resistance (both internal and external), and

operating temperature. Materials available for umbilical construction

include a range of materials from carbon steel to super duplex.

External corrosion protection, afforded by a bonded polymer or zinc

sheath, is available when required. Insulation and thermal shielding

are also available upon request.

Figure 2: Steel Tube Umbilical [2]

• Integrated Production Umbilical (IPU)

The IPU design is based on proven technology and qualified for both

static and dynamic application in shallow and deep water. The design

is ideal for contributing to a stronger umbilical and a better protected

flow line. IPU reduces complexity of the field layout, as well as cost

and time in manufacturing and installation.

  6  

Figure 3: Integrated Production Umbilical [2]

• Power Distribution Umbilical (PDU)

PDU is suitable for static and dynamic application. It gives complete

dynamic and electric analysis.

Figure 4: Power Distribution Umbilical [2]

2.2 INSTALLATION METHOD

Umbilical is usually installed in one continuous length. It can weigh as much

as 7000 tons or may be more. As umbilical is in one continuous length, the

possible laying methods is reeling method. After umbilical is laid on seabed,

  7  

usually it is buried to 2 meters depth for protection. Then the umbilical is

terminated at the subsea end using an Umbilical Termination Assembly

(UTA)

Figure 5: One Continuous Umbilical in the Reel [1]

3 RISER

3.1 TYPE OF RISER

A Riser is a conducting pipe connecting subsea wellheads, templates or

pipelines to equipment located on a Floating Production Installation or fixed

offshore structure. [3]. Riser systems are classified into two big categories.

The first category is those that coupled directly to the host facility and the

other category is the un-coupled systems, which in most cases are connected

by flexible jumpers.

3.1.1 COUPLED RISER

• Steel catenary Risers (SCRs)

Steel catenary riser (SCR) technology has emerged as a potential

  8  

solution for subsea field development in deep-water. The

advantage of SCR is the reliability and integrity of such a system

over the life of a field at a relatively lower cost. Steel Catenary

Risers (SCRs) can be installed by all three methods of

installation. J-lay, reel-lay and S-lay. One of the main challenges

in any SCR design is the fatigue performance of the weld, and,

with its extensive welding technology. [4]

Figure 6: Catenary Riser System [5]

• Weight-Distributed SCRs

Weight Distributed SCR’s concept enhances the applicability of

SCRs to harsher environments. In this concept, well-qualified

ballast elements are attached at certain sections of the SCR to

reduce the stresses around the touchdown point and enhance the

fatigue performance of the SCR.

  9  

Figure 7: Weight-Distributed Steel Catenary Riser [6]

• Lazy-Wave SCRs

Lazy Wave SCR has attracted more attention in recent years due

to ts good motion isolation effect between Touch Down Point

and hang off. The main challenges for Lazy Wave SCRs are

high-specification welds and installation issues when all the

heavy buoyancies are attached to the SCR.

Figure 7: Lazy-Wave SCR configuration [6]

  10  

• Flexible riser systems

Flexible riser capable in extending to 800-1800m water depth

depending on diameter and pressure. It is normally assembled

and tested onshore. It usually comes in a reel configuration.

Flexible riser is good for shallow water as motions are decoupled

and reduced fatigue. However, the back draw is that damage can

be occurred and inspection is not easy.

Figure 8: Flexible Riser [5]

3.1.2 UN-COUPLED RISER

• Grouped Single Line Offset Riser (SLOR)

The SLOR offers an attractive solution due to its excellent

fatigue performance and ability for pre-installation, thus taking it

off the field development critical path. The SLOR is typically

situated around 100m away from the vessel or turret depending

on water depth. Connection between the two is achieved using a

flexible jumper via a steel gooseneck assembly connected to the

  11  

top of the riser pipe. The flexible jumper is then connected to the

vessel through an I-tube or J-tube assembly with bend stiffener.

At the base, the SLOR is connected to a foundation pile (suction,

driven, gravity or drilled) and terminated with an off-take

assembly that facilitates connection to the flowline with a rigid

spool. Connection to the foundation pile is achieved via a roto-

latch (articulation joint) or a stress joint.

Figure 8: Grouped SLOR Arrangement [7]

Installation of Grouped SLOR system is by towing, reel laying

and J-laying. It is to confirm the flexibility and the feasibility of

the riser.

• Single Hybrid Riser Tower / Hybrid Riser Tower

Hybrid Riser Towers (HRTs) is field proven has significant

benefits for deep-water riser applications in terms of flow

  12  

assurance, thermal performance and robustness of layout. This is

especially significant when a large number of risers are

considered. An HRT provides the required flexibility by avoiding

a crowded layout and allowing a progressive deployment. The

idea is applicable to deep-water and ultra-deep-water, and to

spread- moored and turret-moored FPSO installations.

Figure 9: Single Hybrid Riser Tower / Hybrid Riser Tower [7]

• Buoyancy Supported Risers (BSR)

The BSR concept consists of a large sub-surface buoy, which is

anchored to the seabed by eight chains, two on each corner of the

buoy. The buoy supports multiple SCRs, which are connected to

the FPSO by non-bonded flexible jumpers. This BSR systems

absorbs the dynamics from the FPSO, resulting in almost no

dynamic stresses on the SCRs, making them behave like a long

free-spanning pipe line with the major fatigue response coming

  13  

from the Vortex Induced Vibration due to the local currents.

Since there is very little dynamic response for the SCRs,

mechanical-lined pipe is used for the SCR section, thereby

optimizing the riser design.

Figure 10: Buoyancy Supported Riser [4]

4 FLOWLINE

4.1 TYPE OF FLOWLINE

The first pipeline was built in the United States in 1859 to transport crude oil.

[8] Through the one-and-a-half century of pipeline operating practice, the

petroleum industry has proven that pipelines are by far the most economical

means of large scale overland transportation for crude oil, natural gas, and

their products. Pipelines have demonstrated an ability to adapt to a wide

variety of environments including remote areas and hostile environments.

Transporting petroleum fluids with pipelines is a continuous and reliable

operation.

Flexible pipes have been introduced in the oil industry since 1972, when

  14  

Coflexip was awarded a patent to build a high pressure, flexible steel pipe.

The first application of flexible pipeline was used in drilling as a 15,000 psi

Kill and Choke line. [9] Since then, flexible pipe designs have improved to

produce the flowlines and risers that are now used in the offshore oil

industry.

For deepwater, the flexible pipes are used mainly for dynamic risers from a

subsea pipeline end manifold (PLEM) or riser tower to a floating production

system such as an FSO, FPSO, and TLPs. The other uses are static risers,

static flowlines, subsea jumpers, topside jumpers, and expansion joints.

Flexible pipes are used for versatile offshore oil and gas applications

including production, gas lift, gas injection, water injection, and various

ancillary lines including potable water and liquid chemical lines.

4.2 FLOWLINE INSTALLATION METHOD

Pipe-laying encompass installation methods whereby the pipe string is

welded together from pipe joints, before the welds are inspected for defects

and coated, all onboard a specialized pipelay vessel as it is installed on the

seabed. [10] Pipe-laying method is used not only to install pipeline

(Flowline) but also umbilical and riser as these items are grouped together.

There are several types of SURF installation method that being used until

now. They are: Towing Method, S–Lay, J–Lay, and reeling. Here we will

discuss further for each method of SURF installation method.

4.2.1 TOWING METHOD

Tow method is one of the installation method that still being used

until now. In the tow methods, the pipeline is normally constructed at

  15  

an onshore site with access to the water (sea-front). These methods

can be used for installing pipelines across inland lakes, across wide

rivers, and offshore.

In the case of an offshore pipeline, the pipeline is welded onshore

with an onshore pipeline spread. Once the pipeline is fabricated and

hydro-tested, the pipeline is dewatered and moved into the water,

while being attached to a tow vessel. It is then towed to a location

offshore where each end is connected to pre-installed facilities. This

method could be cheaper than using a lay barge spread to install the

pipeline offshore. The advantage occurs mainly if several small lines

need to be laid and can be bundled inside a larger pipe.

The pipeline can be made up either perpendicular or parallel to the

shoreline. For a perpendicular launched pipeline, a land area that can

accommodate the longest section of the fabricated pipeline must be

leased. A launch way consisting of a line of rollers or rail system

needs to be installed leading from the shore end right into the water.

Launching Method

A good arrangement of pipeline fabrication should be made prior

pulling it into the seawater. After all the sections of pipeline are

fabricated and tested, the first section of pipeline is lifted by side

booms and placed on the rollers on the launch way. The cable from

the tow vessel is attached and the section is pulled into the water,

leaving sufficient length onshore to make a welded tie-in to the next

section. In this manner, the whole single pipeline is fabricated and

pulled into the water. A holdback winch is always used during these

  16  

pulls to maintain control the direction of pull.

Figure 11: Pipeline Launching [5]

In the parallel launch method, it is required to have a land area along

the shore as long as the total length of the pipeline to be towed. This

could be longer than that acquired during perpendicular launch.

Parallel launch does not require any launch way. After the sections of

the pipeline are welded and tested, the sections are strung along the

shoreline. The pipeline sections are welded together to make up the

length of pipeline to be towed. The completed pipeline is moved into

the water using side-boom tractors and crawler cranes for the end

structures. The front end is attached to the tow vessel, while the rear

end is attached to a hold back anchor. The anchored tow vessel

winches in the tow cable in such a manner that it gradually moves the

pipeline laterally into the water, while the curvature is continuously

monitored. When the whole length of pipeline and its end structures

make one straight line, the tow vessel begins to tow the pipeline along

the predetermined tow route.

For pipelines that are to be towed into deep water, pressurized

nitrogen can be introduced into the pipeline to prevent collapse or

  17  

buckling under external hydrostatic pressure. A depth of 3000 feet

can be achieved. Greater depths would require a stop for another

recharge of pressurized nitrogen from the surface.[11] This has never

been done.

Maintenance

Maintenance for towing method can be varies. For shallow depth

water, the maintenance is still can be done by diver. But for very deep

water, It will require Remote Operating Vehicle (ROV). It all goes

the same for any very deep water application.

Towing Method

Towing method can be classified into 5 types. They are Bottom Tow

Method, Off-Bottom Tow Method, Controlled Depth Tow Method,

Catenary Tow Method and Surface Method. The choice of method is

dependent on the submerged weight of the pipeline, length of the

pipeline and the seabed environment or presence of existing pipelines

along the selected tow route.

4.2.1.1 BOTTOM TOW METHOD

The bottom tow method is pulling the pipeline along the

seabed to its final location. The length of a single section of

pipeline is limited by the available bollard pull of the vessel

used. The bollard pull must be greater than the total

submerged weight of the pipeline plus the friction. Two to

three vessels can be used in tandem to obtain additional

bollard pull capability.

  18  

Figure 12: Bottom Tow Method [12]

A thorough sea-bottom survey of the pipeline all the way

from the shoreline to the pipeline’s final resting place

offshore shall be conducted prior pulling it into its final

location. An abrasion-resistant coating is required on the

bottom half of the pipeline to protect the normal corrosion-

resistant coating like FBE. However, abrasion testing may be

required to select the appropriate coating. A slick coating on

the bottom half of the pipe can reduce friction and reduce the

bollard pull requirement during tow. If concrete weight

coating is required for stability, then this can be that coating.

An additional thickness may be required to allow for

abrasion.

For pipelines in shallow water, a trench may be required due

to regulatory requirements or for pipeline stability. In this

  19  

case, a subsea trenching plow can be prepared and attached

ahead of the pipeline prior to pulling it into its final location.

In bottom tow method, it is difficult to pull the pipelines into

a curved trench. This will require additional bollard pull.

The ends of a bottom-towed pipeline are normally connected

by deflect-to-connect method. In this method, the end

sections of the pipeline are made to float a few feet above

the seabed by providing additional buoyancy for this length

and attaching anchor chains at discrete spacing along this

length. The buoyancy and chains are attached onshore with

chains strapped over the buoyancy pipe during towing and

deployed at the pipeline’s final location. This length can then

be pulled laterally by attaching cables to the end of the

pipeline from the facility. Once the pipeline end structure is

secured at the facility, the connection can be made by

flanges (in diving depth) or by hydraulically activated

connectors (in deepwater).

4.2.1.2 OFF-BOTTOM TOWING METHOD

In the off-bottom tow method, the submerged pipeline is

buoyant and floats above the seabed at a predetermined

height during the towing. The connection at the ends of

bottom-towed pipeline is achieved in the similar method as

Bottom tow method. The buoyancy and chains are attached

in discrete modules for the length of the pipeline.

In Off-Bottom Tow Method, no extensive protection

  20  

structure is required and existing pipelines can be crossed by

placing concrete mats placed over these pipelines and

allowing the hanging chains to drag over the mats..

However, buoyancy and chains are required for the entire

length of the pipeline. If several pipelines are needed for

field development, the buoyancy and chains can be

recovered and used again.

Figure 13: Off-Bottom Tow Method [12]

The seabed survey needs to consider only obstacles that are

higher than the height of the floating pipeline and sudden

steep seabed cavities. An abrasive-resistant coating is still

required in Off-Bottom Tow Method, but not as stringent as

Bottom Tow Method.

Off-bottom tow is only feasible up to a certain depth because

the buoyancy becomes more expensive as the water depth

increases.

  21  

4.2.1.3 CONTROLED DEPTH TOWING METHOD

In Controlled Depth Tow method, the entire length of

pipeline is controlled and kept at a considerable height above

the seabed in between the lead and trailing tow vessels

during towing. To achieve this, discrete buoyancy, chains,

and a large tension applied to the pipeline are required. The

tension is applied by two tow vessels pulling in opposite

directions at each end of the pipeline. The pipeline is

controlled at certain depth and once it reaches its desired

depth, the front tow vessel applies more thrust while the

back tow vessel cuts back on its reverse thrust. A third vessel

is required to monitor the height of the pipeline in the middle

by using a subsea transponder system. This vessel sends its

signal to the two tow vessels, which see the height in real

time and adjust their thrusts appropriately to keep the

pipeline within the desired depth range. At the design tow

speed, the pipeline will lift off from the seabed and adopt the

desired mid-depth CDTM configuration. The lift is

dependent on speed, type of chain and number of links. By

controlling the tow speed and tow wire length, the pipeline

configuration is maintained within acceptable limits, as

defined by static and dynamic tow analyses. This method is

not suited for very long pipelines (greater than 3 miles). [9]

  22  

Figure 14: Controlled Depth Tow Method (CDTM) [12]

In this method, only a near shore survey and final infield

pipeline route survey are required. Incase of emergency,

some discrete areas where the pipeline can be parked shall

be identified. CDTM tow speed is higher than for off-bottom

tow, and the absence of contact with the sea bottom, which

allows passing severe slopes or rocky bottom conditions.

This method is ideal for areas with extensive rocky outcrops,

many existing pipelines, or other obstructions along the tow

route.

4.2.1.4 CATENARY TOWING METHOD

In the catenary tow, the required bollard pull of the two tugs

increases as the water depth decreases. The pipeline being

towed is in a catenary configuration between the tugs. A

catenary tow is not possible in Shallow water depth since the

required horizontal bollard pull forces to keep the pipeline

  23  

sag-bend of the seabed are too high for conventional tugs.

The installation on site is achieved by paying out on the tug

winch wires while controlling the touchdown routing with

the vessel position.

Figure 15: Catenary Towing Method [12]

4.2.1.5 SURFACE TOW METHOD

Surface tow method is similar to mid-depth tow method but

it will not require any chains. This method required the two

vessels at each end to keep the pipeline in tension while it is

towed on the surface. Only a survey of the final pipeline

route is required. This method can be used for shallow. For

deep water, a sophisticated controlled flooding and/or

buoyancy removal system is required. Not many pipelines

are installed by this method.

  24  

Figure 16: Surface Tow Method [6]

4.2.2 S-LAY METHOD

S-Lay method is the most common installation method of subsea

umbilical, riser and flowline in shallow water. Typically 12 meters

long of pipe joints are manufactured and coated onshore. Then, they

are brought to the pipe lay vessel by supply vessels so that the pipe

construction can be continued without interruptions. In the S-lay

method, the welded pipeline is supported on the rollers of the vessel

and the stinger, forming the over-bend. Then it is suspended in the

water all the way to the seabed, forming the sag-bend. The over-bend

and sag-bend form the shape of an “S”. Typical S-Lay method

configuration can be seen at figure 17, below.

  25  

Figure 17: Schematic of S-Lay Method [13]

Onboard the S–Lay vessel, the pipe joints are welded on to the end of

the pipeline in a horizontal production facility. It is called the firing

line, which provides a sheltered environment for the workers to carry

out multiple workstations for welding, non–destructive testing of the

welds and coating. The field joint station is located after the NDE

station and the tension machines. The pipeline is held in a tensioner to

facilitate continued construction. Tensioner is a large rolling

caterpillar tracks with rubber pads that press on to the pipe going

down to the seabed. The tensioners control the speed (pay-out speed)

when the pipe that has been welded with the new pipe joints extended

from the vessel. This speed is controlled while maintaining the

tension on the pipe as the vessel moves forward. A sloping ramp

supports the pipe as it moves from the vessel and onto the stinger.

The stinger is a long open frame structure fitted with rollers, which

supports the pipeline and controls its curvature from the horizontal to

  26  

the inclined section. The stinger is typically made out of several

hinged sections to make it articulated. Setting the segments at chosen

angles can control the stinger’s shape and curvature. The overall

stinger length depends on the pipelay vessel, but is typically in the

range of 100 meters. In shallow water depth of 100 meters, the lift off

angle will typically be in the order of 30◦ from the horizontal. For

increasing water depth, the lift off angle also increases up to 90◦ if the

tension is kept within practical limits. This is commonly known as

Steep S–lay [14], which can be performed by vessels like the

Solitaire. This stinger configuration has shown to reduce the tension

in the pipe compared to the traditional S–lay method. Furthermore,

pipeline engineers argue that it will be safe to relax the standard strain

level of the design in order to reach greater depths and handle even

heavier pipelines. [14]When the new pipe length has been laid out,

the whole process is repeated.

Figure 18: S-Lay Offshore Vessel [13]

  27  

The main advantage with the S–lay method is that the long firing line,

running from bow to stern, enables parallel workstations for assembly

of pipe joints, such that up to four pipe joints can be added at the

time. This makes the method fast and economical, particularly for

long pipelines.

However, for very deep water, the pipe must be supported to a near

vertical departure angle. It requires a very large stinger to avoid pipe

damage. With increasing water depths, the power that’s required to

provide lay tension increases. It is indirectly transferable to high fuel

expenses.

4.2.3 J-LAY METHOD

J-Lay installation method is a development from S-Lay installation

method and often seen as complementary methods. [14] J-Lay

installation method eliminates the over-bend region in S-Lay

installation method when installation is required in deep-water. The

configuration of the pipeline from the seabed to the pipelay vessel is

near vertical at the pipelay vessel end and this suspended pipe

resemble of letter J. The pipe leaves the pipelay vessel in a nearly

vertical position in the J–lay installation method.

  28  

Figure 19: Schematic of J-Lay Method [13]

The pipeline is constructed on a vertical ramp, the so–called J–lay

tower, which is fitted with tensioners and workstations. The angle of

the J–lay tower may typically vary between 0◦ and 15◦ from the

vertical. The ramp angle is chosen in such a way that it is in line with

the pipe catenary to the seabed. The pipe leaves the barge steeply

such that the total length of the free pipe is shortened and less applied

tension is required for sag bend control. The touchdown point is not

as far behind the vessel as for S–lay, due to the lower applied tension,

so that positioning of the touchdown is easier, and the pipe can be

installed more accurately. The pipeline is only bent once during

installation (at the seabed) which is advantageous for installing

pipelines that are sensitive to fatigue. Also the complexity involved

with a stinger is eliminated. The main drawback with the method is

that the tower only facilitates one workstation, making the J–lay

method inherently slower than the S–lay method, which is the price

  29  

paid for pipe installation at greater depths. But since the large J-lay

towers are capable of handling prefabricated quad joints (160 feet

long), the speed of pipe-laying is increased.[offshore pipelines] The

added weight high up on the vessel has an adverse effect on stability,

and semi–submersibles are frequently used to facilitate J–lay due to

their high stability. The J-lay method is very suitable for deep water

as the pipe leaves the lay system in an almost vertical position. J-Lay

installation method is not applicable in shallow water.

Figure 20: J-Lay Offshore Vessel [9]

4.2.4 REEL-LAY METHOD

Reel-Lay method is a method of installing pipelines in the ocean from

a giant reel mounted on an offshore vessel. Depending on the type of

lay vessel the spool can be designed to operate in the horizontal or the

vertical position. Pipelines are assembled at an onshore spool-base

  30  

facility and spooled onto a reel, which is mounted on the deck of a

pipelay barge. Reel-Lay method results in greater productivity due to

the ability to lay the pipe in a continuous manner by unwinding it

from the reel. The Reel-ay method reduces labor costs by permitting

much of the welding, x-raying, corrosion coating, and testing to be

accomplished onshore, where labor costs are generally lower than

comparable labor costs offshore. As the pipe is already spooled in the

reel, It reduces the number of personnel required to lay the pipe. Low

manpower required means lowering the risk of accidents at the same

time and providing efficiency in the availability of the pipe.

Figure 21: Reeled Pipeline [15]

Each spool is designed to operate with a specific barge and can

usually handle pipe from 2" to 12". The total length capacity depends

on the spool dimensions and the diameter of the pipe. Based on a

typical design, a spool can hold up to 80 km of 2" pipe. [16]

The normal procedure used to spool the pipe on the reels consist in

welding the joints of pipe in the operations yard and winding them

  31  

concurrently on the spools. This procedure could be performed

directly on the docked barge since handling a full reel would require a

large crane to load the spool aboard. Therefore, at the time of

considering this method, it is necessary to clearly know that the lay

barge would have to stay docked while the pipe is being welded and

wound on the spool. Otherwise, a large enough crane is required, as

well as an adequate support and pipe-stringing track must be

provided.

The productivity Reel-Lay method depends on various factors

including the length of pipeline sections to be laid, the distance

between risers, the number of lay-barge repositioning required could

limit the production. If the wells and flow stations are close together

and the average length of this pipe laying is quite short (1500 – 2000

m), a good sequential drilling program in the surrounding areas would

be required to obtain the largest amount of laying job within the

adjacent areas and to avoid long distances mobilizations between

work sites, this method can result in a high productivity. Another

factor that affects productivity is the method used to move the barge

during the pipe lay. If the conventional method using winches and

anchors is used, the productivity is greatly reduced than using an

automated dynamic positioning system.

Reel-Lay method has some limitation where the pipeline is plastically

deformed and then straightened again, some thinning of the wall and

loss of yield strength of the material can be occurred. It also cannot

reel concrete-coated pipeline.

  32  

4.3 EVALUATION OF SURF INSTALLATION METHOD

After elaborating all available SURF installation method, we will try to

identify the pro and cons for each installation method. Every installation

method should have their own strong points, but they also have their own

weaknesses. Here we will try to evaluate and compare the advantages and

disadvantages for each installation method so that it can become our

guideline in choosing the best installation method for certain well.

Towing Method

Basically the main advantage of towing method is that the pipelines,

umbilical or riser can be fabricated onshore before it will be towed to the sea.

This onshore fabrication can save a huge cost compare to offshore. Actually,

Tow methods can be used for installing pipelines from shallow water depths

to deep- water depths depending on the design requirements but it has a lot

of drawbacks. The biggest drawback for Towing Method is that this method

is very dependent to weather; sea current, tide and also limited to certain

depth of 3000 feet even though pressurized nitrogen has been introduced to

the buoyancy system. The other drawbacks are different for each type of

Towing Method.

• Bottom Tow Method and Off-Bottom Tow Method

Bottom Tow and Off-Bottom Tow Method are similar and it requires

a seabed survey prior to towing to make sure that there is no

obstruction or cross pipelines on the seabed. Abrasive-resistant

coating or additional thickness for concrete pipe is required to

prevent from severe corrosion

  33  

• Controlled Depth Tow Method

Controlled Depth Towing Method required additional vessel to check

and control the depth of the pipeline being towed. It means additional

cost is required. CDTM is also not suitable for pipeline more that 3

miles.

• Catenary Tow Method

Catenary Tow Method is not possible for shallow water and it

requires additional bollard when doing deeper towing. It can be done

by combining few vessels to pull the pipline.

• Surface Tow Method

Surface Tow Method doesn’t require any chain, but it requires a lot of

buoyancies. As the pipeline is floating almost at surface, sea current

and weather give a huge impact to it. When the depth goes deeper, a

sophisticated controlled flooding and/or buoyancy removal system is

required. This is why this method can only be used for shallow water

and not many pipelines are installed by this method.

S-Lay Method

The main advantage with the S–lay method is that the long firing line,

running from bow to stern, enables parallel workstations for assembly of

pipe joints, such that up to four pipe joints can be added at the time. This

makes the method fast and economical, particularly for long pipelines.

However, for large water depths, the pipe must be supported to a near

vertical departure angle, which requires a very large stinger to avoid over

bending which damaging the pipe. With increasing water depths, the power

needed to provide the required lay tension increases, which is directly

  34  

transferable to high fuel expenses. These are the main disadvantages of the

method.

J-Lay Method

The J-lay methodology is the prime technique for laying pipelines in very

deep waters. Vertical space configuration on a J-lay vessel allows for only

one pipe joining station, hence a fast and reliable pipe-joining technique or

multiple pipe sections are prerequisite for practical use of J- lay method.

J-Lay Method allows the pipe to be laid in a less tension configuration. Pipe

stresses are maintained well within the linear elastic limit. J-Lay Method also

requires lower lay tension resulting in reduced on-bottom tension and free

span. As the vessel required a huge tower, it adds more weight to overall

weight of the vessel and increased its stability. Hence, It is less susceptible to

weather condition. As the J-lay method is primarily a deep-water method,

some limitations occur in shallow water.

Reeling Method

Reeling Mehod hold a huge advantages to be able to lay very long pipelines.

But, It is only limited to flexible pipelines only. This flexible pipelines

cannot be used for ultra deep water as the flexible pipelines cannot withstand

the hydrostatic pressure from seawater. Removing the buckle in reeling

method takes quite time to complete.

4.4 OFFSHORE VESSEL SELECTION

Since the first SURF installation method has been introduced, the vessel to

carry out the job has been improved to give better performance. Selection of

vessel is vital in Subsea Umbilical Riser and Flowline installation to be able

  35  

to perform the job. It is very important to understand the primary vessel-

capacity requirements to carry out the job. Some information like; crane-lift

capabilities, flexible-pipe lay tensions and overall deck-storage capacity have

to be identified before handling the products to be installed. There are many

types of vessel that normally used to carry out SURF installation such us:

Tug Boat, Barge, FSO/FPSO, etc. To determine the installation-vessel

requirements, some initial engineering was conducted to better understand

maximum lift and deployment loads associated with the installation program.

Figure 22: Type of Offshore Vessel [17]

  36  

CONCLUSION

As we know, Umbilical, flow-line and riser installation operations are an

essential part of subsea construction. Compared with fixed platform solutions,

development solutions applying floaters and or SURF solutions will be

increasingly important. There are a lot of wells in the whole world that required

subsea construction and each places are unique. It doesn’t mean that we can

apply same subsea construction design for well that has different characteristic.

Subsea engineer must understand for each characteristic, which application can

give the best result.

For shallow deep water, S-lay installation method and Towing method would be

the best choice to lay the pipeline on seabed. When doing Towing method, It

would be best if we don not use parallel launching, as it will need large of place

to launch the pipeline in parallel. In the other hand, for deep water J-Lay

installation method is the pioneer. J-Lay method requires a huge vessel with the

tower. Hence, It would be able to withstand harsh weather, as it is more stable.

For small pipeline size, Reel-Lay method could deliver good performance except

for ultra deep water. The flexible pipeline in Reel-Lay method cannot withstand

the huge hydrostatic pressure.

As for Riser, Group SLOR, Single Hybrid Riser Tower / Hybrid Riser Tower,

Steel catenary Risers and Buoyancy Supported Risers are able to be used in deep

water. Group SLOR and Single Hybrid Riser Tower / Hybrid Riser Tower are

famous in their robustness in layout. In shallow water Lazy-wave Riser

installation would perform well.

In deep water, maintenance is usually done by ROV. It has better safety compare

to Diving maintenance as in Diving maintenance, the diver are exposed directly

  37  

to the environment. Hence it is also advised diving maintenance can only be done

for maximum 30 meters depth only.

In overall, the choice of subsea construction will be depend on the field

characteristic, client requirement and available technology.

  38  

REFFERENCES

[1] INTSTOK, Equipment and systems for offshore oil & gas field developments,

2012

[2] Aker Solution, Subsea Umbilicals, 2009

[3] ABS, Subsea Riser System, 2006

[4] Subsea 7, Riser Technology, 2012

[5] Bernie Alistair, Lecture Notes -Subsea Construction and Support Operations,

2012

[6] http://www.offshore-mag.com

[7] Grouped SLOR

[8] (Wolbert, George S., Petroleum pipelines; Petroleum industry and trade;

Petroleum pipeline industry, 1952

[9] Boyun Guo, et al, Offshore Pipelines, 2004

[10] Braestrup et al., Marine Pipelines, 2005

[11] Alf Roger Hellesto, et al, Deep Water Pipeline and Riser Installation by the

Combined Tow Method, 2007

[12] http://www.bgr.bund.de

[13] Gullik Anthon Jensen, Offshore Pipelying Dynamics, 2010

[14] Dominique Perinet, Acergy France and Ian Frazer, Strain Criteria for Deep

Water Pipe Laying Operations, 2008

[15] http://www.oilonline.com

[16] http://www.welschs.cc/reel.html

[17] http://gcaptain.com/technip-begins-work-marine-containment/

  39