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Lesson Overview: Pipelines and Flowlines

New methods and high-tech vessels have brought major new capabilities and cost savings to the construction, installation and operation of pipelines/flowlines.

o Introductiono Construction/Installation

Onshore Construction• Surface, Mid-Depth and Off-Bottom Tow• Reel Barge

Offshore Construction• S-Lay• J-Lay

o Seafloor Topology and Current Issueso Subsea Connectionso Repairo Flow Assurance

Inhibitor Injection Pigging Temperature Control Slug Flow/Sand Erosion

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Introduction

In deep water, several factors increase pipeline/flowline cost and technology challenges.

Challengeso Higher pressure and lower temperature at the seafloor

o Production coming from deeper reservoirs at higher temperatures and pressures

o Greater distances from subsea wells to floating facilities

o Facilities farther from shore

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Flowlines reach extreme depth and distance

Subsea tiebacks are dominating deepwater development, reaching beyond 9,000 ft WD and almost 45 miles (oil) and 90 miles (gas) distance.

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Learning Objectives

You will learn the current technology for deepwater pipeline/flowline:

o Construction/installation

o Repair

o Seafloor Connection

o Flow Assurance

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What part do pipelines and flowlines play in offshore installations?

Pipelines carry product, usually partially processed, from offshore facilities to shore.

Flowlines transport product produced from subsea wells, either to manifolds where it is commingled or directly to a floating facility.

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Pipeline/flowline construction and installation methods

Onshore construction plus winding on a reel and then unreeling offshore from a reel vessel

Onshore construction followed by towing to the offshore site by:• Surface tow• Mid-depth tow• Near-bottom tow

Offshore construction (on the pipelay vessel) and installation by:

• S-lay• J-Lay

We will now discuss each method.

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Towing Pipelines on the Surface

Pipelines can be fabricated on the beach, then towed out with buoyancy attached. When the buoyancy is reduced on location, and/or the pipe is flooded, it submerges.

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Towing Pipeline Mid-Depth and Off-Bottom

To prevent damage from wave forces, the pipeline may be towed submerged.

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Off-bottom

Depth controlled by buoyancy and dragged

chains

Mid-depth

Suspended between two boats

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Onshore Flowline Construction and Laying from a Reel Vessel

Smaller diameter line is fabricated onshore and then wound onto a large reel, as much as 200 ft in diameter. It is deployed offshore from a reel vessel, straightened as it is laid.

The first video (WV-10) is a horizontal reel vessel capable of laying two lines simultaneously. The second video (SS7-1) shows how the line is fabricated and loaded onto a vertical reel vessel.

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S-Lay Technique for Laying Pipe

In the illustrations and videos so far, we have seen pipe deployed from the vessel by the S-lay technique. The pipe releases horizontally from the back of the vessel and then bends downward over a stinger. Tension is maintained in the pipe, causing it to bend gently back to horizontal when it reaches the seabed.

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S-Lay Stinger

Stinger: A curved steel structure with rollers that protrudes from the stern of the pipelay vessel and limits the bending radius of the pipe

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Construction and Deployment from an S-Lay Vessel

The second video (WV-14), shows details of the fabrication and inspection operations on an actual pipelay vessel, the Solitaire.

WV-9, WV-14

The first animation (WV-9) illustrates how pipeline/flowline is fabricated and laid as the pipelay vessel moves along the prescribed route. This is a typical method for laying larger diameter pipelines.

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J-Lay Technique for Laying Pipe

A more complex method, J-lay is generally employed for deep water due to the high tension caused by the weight of the long, suspended pipe.

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The pipeline is fabricated vertically in a gimbaled tower and lowered vertically to the seabed where it bends to the horizontal (assuming a J curve). The tower is usually gimbaled to accommodate vessel motions without inducing bending stresses in the pipe.

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J-Lay Technique, cont.

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Two of the largest crane barges in

the world, Heerma Balder and

Saipem 7000, (shown) have been

retrofitted with J-lay towers.

Saipem

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J-Lay on Crane Barges, cont.

These huge crane barges can J-lay prewelded, 160-ft joints of pipe, reducing the number of welds required in the tower.

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J-lay video: This (WV-8) animation shows how fabrication is accomplished in the vertical tower. Notice the multiple set of tractors for supporting the pipe’s weight.

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The Heerma Balder can J-lay 30-in. diameter pipe in up to 10,000 ft water depth (2.6 MM lb).

Heerma

Saipem 7000

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Subsea 7 Ship

Like the Seven Borealis, below, some new vessels are equipped for both S-lay and J-lay.

The large pipelay vessel shown in this animation (SS7-2) is capable of both J- and S-Lay operations. Its large capacity and simultaneous operations capability gives it cost advantage for the installation of deepwater fields with extensive pipelines/flowlines.

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Exercise

1. Define the J-Lay technique for laying pipeline.2. Define the S-Lay technique for laying pipeline.3. What are the two kinds of barges used in pipeline

construction?4. Why is deepwater pipeline construction so

expensive?5. What are two methods of towing pipe?

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Seafloor Topology

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The seafloor is often not flat and soft. Canyons, mounds, escarpments, even small mountains can present major obstacles for pipelines.

To avoid damage during pipe laying and to preclude long, unsupported spans, the seafloor must be surveyed to find a suitable pipeline route.

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In many areas there are significant currents at the seafloor.

Hydrodynamic drag can move unburied pipeline on or near the seafloor.

Unsupported spans are subject to Vortex Induced Vibrations (VIV) that can lead to fatigue failure.

Seafloor Topology and Seafloor Currents

One of the worst seafloor challenges was the Orman Lange project offshore Norway, seen in this video (WV-25). Vibration monitors were installed to record any vibration.

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Orman LangePipeline Span

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Seafloor Topology and Seafloor Currents, cont.

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RJ Brown

When long spans and high

seafloor currents are

possible, the pipeline may

be fitted with strakes to

suppress VIV.

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Even flowline jumpers

may require strakes.

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Subsea Connections

The ends of pipeline/flowlines are connected to seafloor facilities and wellheads by remote operations. Many ingenious techniques have been devised. Here are a few:

Vertical Connections

An illustration of a wellhead connected to a manifold with a jumper

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A subsea manifold connected to many wellheads

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Subsea Connections – Vertical

1.The remote tools, carrying the ends of the jumper, are lowered over the upward-looking receivers. 2. The connectors are closed and sealed by hydraulic power. 3. The tools are retrieved.

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Subsea Connections – Horizontal - I

A previously laid line was terminated at a base with a guide post. First using the sleeve, then by fine positioning in the tool, the ends are merged. The connector is closed, sealed and tested.

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Subsea Connections – Horizontal - II

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1. A wire connected to the end of the new pipe pulls it close to the receiver on the facility. 2. The ROV guides the pipe head into the receiver as the wire pulls it. 3. The ROV then locks, seals and tests the connector.

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Subsea Connections – Horizontal - III

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This animation (WV-31) shows an elaborate North Sea technique for seafloor joining of two pipeline segments.

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Exercise

1. Explain why and how a strake is employed.2. Give an example of ROV use in subsea connector utilities.3. What is VIV and how can it be dealt with?4. Describe how vertical or horizontal connectors can be employed remotely on the

seafloor.

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Repair

A major challenge is repair of damaged deepwater pipelines.

The schematic shows cutting out a section of the pipeline containing the damage, removing and replacing it with the help of an ROV*.* Remotely operated vehicle

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Repair, cont.

A crane lowers a section of pipeline for the repair.

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Repair, cont.

Chevron has developed and fabricated a deepwater pipeline repair system. It is stored on the Gulf coast for shipment when needed anywhere in the world.

This video (WV-19) explains the Chevron Deepwater Pipeline Repair System, which is similar to other operations.

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Repair, cont.

In the Chevron video, we saw that damaged pipeline needs to be cut and the ends prepared for insertion of a new section. The Wachs® Subsea diamond wire saw, deployed by an ROV, was used.

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This is a (WV-23) demonstration of the Wachs diamond wire saw which is capable of cutting pipe up to 24-in. diameter.

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Exercise

1. Describe the principles of Chevron’s DW PR system.

2. What is an ROV?3. How is an ROV instrumental in deepwater pipeline

repair?

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Flow Assurance

All pipelines carrying crude oil and gas tend to become clogged, even on land and in shallow water. In deep water, low temperature and high pressure require various measures to assure pipeline flow. Very briefly, the problems are:

Gas hydrates are ice-like minerals that form crystals at the low temperatures and high pressures in the deep sea. Crystals forming inside pipelines or flowlines can clog the flow.

All crude oil contains some amount of wax (paraffin and asphaltene) that will solidify as the temperature drops.

Corrosion due to corrosive elements in the crude can damage or even breech the line.

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Flow Assurance: Inhibitor Injection

To prevent flow restrictions by hydrates and wax, and to inhibit corrosion, chemicals are injected into the flow. An extensive process is employed to specify the inhibitors and to design the injection system.

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Flow Assurance: Pigging

In addition to inhibition, pigs are pumped through lines to remove the buildup of hydrates, wax and scale on a pipeline’s inner wall. Instrumented pigs can also measure the pipeline wall thickness, detecting corrosion before leaking occurs.

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Flow Assurance: Pigging, cont.

Pigging Operations:

• Pig launchers and receivers must be built into the pipeline during construction.

• A pig is pumped through the line, scraping the wall and pushing the buildup out through the pig receiver.

This video (WV-24) of the Pipeline Engineering Automatic Pig Launching System illustrates pig launching and retrieval.

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Flow Assurance: Temperature Control

For long flowlines carrying very hot product from very deep wells, chemical injection and pigging may be insufficient or not cost effective.

Another option is to reduce heat loss by coating flowlines with insulation.

Constructed “pipe-in-pipe” uses the outer pipe to protect the insulation against the harsh environment of installation and seabed survival.

Extensive design analysis and testing are required.

Courtesy Bredero Shaw GR-168

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Flow Assurance: Temperature Control, cont.

Pipe-in-pipe construction protects the insulation during installation and in service.

Designs of pipe-in-pipe insulated flowlines requires extensive thermal analysis and testing.

PIP (pipe-in-pipe) Pipeline/Flowline Insulation Technique

Testing Finite-Element Thermal Analysis

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Flow Assurance: Temperature Control, cont.

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Complex pipe-in-pipe designs can incorporate fluid and electrical heating sources to deal with highly viscous oil.

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Flow Assurance: Slug Flow and Sand Erosion

Two additional problems are slugs in two-phase flow (liquid and gas) and sand erosion. Solutions to these problems are more difficult in remote, deep water.

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Liquid collects at depressions in the pipe, cleared only when the gas pressure behind it builds up sufficiently.

Uneven flow results.

Rising and falling pressure causes pipe vibration and disruptive conditions at the pipe exit.

An active system of pressure sensors and variable chokes may be required to break up the slugs.

Slug Flow

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Flow Assurance: Challenging Example

Anadarko’s new Independence Hub platform in 8,000 ft WD presents a major challenge to uninterrupted hydrocarbon flow.

o 20+ tiebacks (totaling over 176 miles)

o Farthest tieback: 45 miles

o Deepest wellhead: 9,000 ft WD

o Pipeline: 135 miles to near shore terminal

Underwater view of Independence Hub in the GoM shows its flowlines and risers.

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Exercise

1. What natural occurrences impede pipeline flow?

2. What is a pig and how does it solve a problem in pipeline flow?

3. How can insulating the pipe help pipeline flow?

4. What is pipe-in-pipe insulation?

5. How did Anadarko solve its flow problems at great depths?