Building a unique collaboration between industry, government, research and community to improve marine science and ensure a competitive and responsible future Blue Economy off Western Australia.

Independent review of the effects of decommissioning offshore infrastructureInformation paper for stakeholder discussion and identification of issues and opportunities

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Disclaimer

This report has been prepared on behalf of and for the exclusive use of WAMSI/ APPEA, and is

subject to and issued in accordance with the agreement between WAMSI/ APPEA and Advisian.

WAMSI/ Advisian accepts no liability or responsibility whatsoever for it in respect of any use of or

reliance upon this report by any third party.

22.5.16

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Table of Contents

1. Project Overview................................................................................................................... 4

2. Project Scope ......................................................................................................................... 5

2.1 Project Area .............................................................................................................. 5

2.2 Infrastructure ........................................................................................................... 5

2.3 Impacts and opportunities .................................................................................. 5

3. Main infrastructure locations in WA ............................................................................. 6

4. Decommissioning options and techniques ................................................................ 9

4.1 Topsides ................................................................................................................... 10

4.2 Jacket ........................................................................................................................ 10

4.3 Floating Production Storage and Offloading units (FPSOs) ................. 10

4.4 Subsea systems ..................................................................................................... 11

4.4.1 Gravity base structure options ...................................................................... 11

4.4.2 Wells ........................................................................................................................ 11

4.5 Pipelines and flow lines ...................................................................................... 11

5. Infrastructure examples ................................................................................................... 12

6. Next steps… .......................................................................................................................... 17

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1. Project Overview

It is estimated that over one hundred offshore installations will need to be decommissioned in

Australia over the next twenty five years. As much of this infrastructure is in WA, WAMSI and

partners: WAFIC, Recfishwest, APPEA, Australian Energy and Resources Growth Centre, Department

of Industry Innovation and Science, NOPSEMSA, WA EPA, and the WA State Government, have

instigated an independent review of the effects of decommissioning. This project will identify

stakeholder issues, concerns and opportunities that will highlight gaps in existing knowledge and

inform a global literature review of relevant decommissioning practices.

Following the Blueprint for Marine Science 2050, the Marine Science Round Table 2015 meetings

agreed the joint funding of this project was a priority for a number of sectors including: State and

Commonwealth regulators, the oil and gas industry, and commercial and recreational fisheries,.

Consistent with the Blueprint approach, this project is the first phase in a three phase effort to

improve the understanding of decommissioning strategies, recognise gaps and better define the

science needs. A decision on subsequent stages will be made through the Blueprint initiative after

this project is complete.

Figure 1. Potential program steps under the WAMSI Blueprint initiative.

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2. Project Scope

2.1 Project Area

The area of the project will include all Western Australian State and Commonwealth waters with an

initial focus of the Timor Sea, north-west and west coast, and secondary focus on the south

coast/GAB. The water area is the high water mark out to Australia’s Exclusive Economic Zone (EEZ)

or 200 nautical miles from the baseline.

Activities in other Australian oil and gas provinces (eg Victoria) will not be included.

2.2 Infrastructure

Infrastructure in the project includes:

Platforms

Pipelines (and any protection such as armouring)

Wellheads

Other subsea infrastructure

Terrestrial activities such as coastal processing or production facilities, jetties, wharfs and waste

treatment facilities are not included.

2.3 Impacts and opportunities

All direct environmental, socio-cultural and economic impacts will be considered.

Although the liability of infrastructure is an important issue, this is not within the scope of this

project and will be considered separately.

Engineering costs will not be considered.

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3. Main infrastructure locations in WA

Figure 2. Pipelines and trunklines in WA

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Figure 3 Existing and proposed production facilities and pipelines on the north west shelf

Figure 4. Existing and proposed production facilities and pipelines in the Timor Sea

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Figure 5. Expected operational life of selected WA oil & gas projects

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4. Decommissioning options and techniques

Decommissioning options include partial or complete removal or leaving the structure in place

(Figure 6).The numerous infrastructure components that make up an operation require different

forms of decommissioning and for each component there are various options and techniques that

may be considered. As operations vary in location, governance, materials and size, the

decommissioning process is different each time, with no option being suitable for every single

situation.

Figure 6. Decommissioning options for offshore installations

Major infrastructure that requires decommissioning at the end of a project may include the

following components:

Surface infrastructure- Concrete gravity and steel platforms including topsides and jackets;

Floating installations- Floating Production Facilities (FPF), Floating Production, Storage and

Offloading vessels (FPSOs);

Subsea systems- well head, production manifolds, anchors, gravity bases; and

Pipelines and flowlines.

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4.1 Topsides

Topsides refer to the upper portion of oil and gas infrastructure which sits above sea level and

outside the splash zone. They are supported by a jacket concrete gravity storage (CGS) or other

floating structure. In most cases decommissioning of conventional steel platforms will include the

removal of topsides and transportation to shore for reuse/recycling or disposal. Several methods

are used for removing installations. The main classifications include:

Reverse installation- is the method whereby topsides are cut into sections and removed in the

reverse order to which they were installed

Piece small- installation is dismantled offshore by cutting or dismantling into small sections

that are shipped onshore in containers

Single lift- Single lift decommissioning involves the removal of the complete infrastructure

component in one piece by a large heavy-lift dedicated vessel (HLV).

4.2 Jacket

A jacket is a large steel frame which supports the topsides and deck of a fixed offshore oil and gas

platform while protecting the piping that connects the topsides to the seabed. Jackets may be

anchored directly to the seabed where depth does not exceed 500 metres. As the majority of oil

and gas projects take place on the continental shelf, more than 95% of the world’s offshore

platforms are jacket designed (IAOGP 2010). Decommissioning of jackets may either involve the

jacket being left in place, partially removed or completely removed.

Leave in place

Leave completely in tact

Topple- Toppling involves severing the jacket from the seabed or higher and letting it fall

sideways onto the seabed.

Partial removal- Partial removal decommissioning involves the removal of the top section of

the jacket, so that the remaining structure sits at a certain depth beneath the water’s surface.

Complete removal

Piece small- As above

Single lift-As above

Buoyancy tanks-Buoyancy tank decommissioning is undertaken by fixing buoyancy tanks

to the four corner legs of the jacket to force the jacket to the surface

Tow in place- Severing the jacket from the seafloor using mechanical or explosive means

and attaching it to a vessel with a cable and towing it to an appropriate reefing site or

deep-water disposal location.

4.3 Floating Production Storage and Offloading units

(FPSOs)

A Floating Production, Storage and Offloading Unit (FPSO) is a floating vessel used by the oil and

gas industry to produce and process hydrocarbons and to store oil.

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The most common decommissioning method for FPSOs is removal and reuse at a different

location. As these structures are floating and not fixed, the use of FPSOs can greatly lessen

decommissioning costs and makes it easier for operators to leave the marine environment as it was

found.

4.4 Subsea systems

4.4.1 Gravity base structure options

Typically, these structures consist of large concrete legs which support the topsides above the sea

with clusters of large concrete oil storage tanks or ‘cells’ at their base. They may be up to 50 m in

diameter, stand in water up to 300 m deep. They can weigh up to 1.2 million tonnes.

There are considerable risks and challenges associated with removing, lifting and transporting the

reinforced concrete legs of gravity based structures. This is recognised by regulating authorities in

the North Sea where complete removal is not legally required. Technical and commercial

constraints have meant that all concrete gravity base platforms decommissioned to date have

obtained permission to leave their substructures in situ. To date, the removal of gravity base

structures has never been attempted in the North Sea (Shell 2016).

4.4.2 Wells

Plugging & Abandonment (P&A) is the process by which a well is closed permanently, usually after

there is insufficient hydrocarbon potential to develop the well, or production has ceased. All wells

must be plugged and abandoned according to regulations when they are no longer in use and

their connecting platform is being decommissioned.

4.5 Pipelines and flow lines

Decommissioning may involve the pipelines and flow lines being removed, left in place unburied or

left in place and buried.

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5. Infrastructure examples

Many offshore Australian oil and

gas facilities have been developed using fabricated steel structures fixed to the seabed

hosting production facilities and accommodation for the associated workers. These are

commonplace in Australia on the continental shelf areas where the water depth is not

excessive such as the North West Shelf in Western Australia. These facilities generally host

wells with “dry trees” – i.e. the well control and isolation equipment is all located above

the waterline on the facility. Generally these facilities are installed with “piles” which are

either drilled or grouted into place or driven into the seabed.

An alternate structure used

occasionally in Australia is to build a “gravity base” from steel reinforced concrete or steel

alone which can be floated into place and sunk into position. This structure sometimes

includes tanks into which crude oil may be stored. Gravity base structures hold the

facilities in place by virtue of their considerable weight on the seabed.

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In shallow waters, typically located

close to islands or the coastline, oil and gas is sometimes produced through very simple

small unmanned facilities such as a “monopod” or small platform with production being

controlled remotely from the nearby island and with production facilities located on that

island.

Transportation of produced oil and

gas to market from offshore facilities utilises primarily standard seagoing tankers (eg, oil,

LPG and LNG) after transference of the product to those tankers. This may be at sea or via

an onshore terminal depending on the installation specifics. Alternatively some

developments pipe their product ashore either as oil or gas via a pipeline for onshore

treatment, storage and then transportation to market. Oil and gas pipelines vary in size

and can be greater than 1 metre in diameter. They are often installed with outer coatings

such as insulation and concrete which acts as additional weight to hold the pipeline in

place. Where the pipeline traverses shallow water such as the shore crossing it may be

bolted in place, have rocks placed over it, be trenched or occasionally installed well below

the seabed in a “tunnel” which has been drilled from the shore.

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In WA, oil

installations frequently feature subsea wells i.e. where the control and isolation equipment

is located on the seabed. Generally oil is stored in oil tankers converted to production

facilities called an “FPSO” or Floating Production Storage & Offloading vessel. Gas is

generally piped to shore from these facilities depending on the quantities involved.

FPSOs are generally

permanently moored or able to be disconnected to avoid severe weather events. Either

way these facilities are removed at the end of their field life and then reused or scrapped

if they are no longer serviceable. FPSOs are held in situ by various means, most commonly

using mooring systems with large steel drag anchors or special piled arrangements such

as suction piles.

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Supporting subsea

developments are a number of common components generally installed onto the seabed known as

Subsea Trees and Well Heads. These are located at the top of the well and provide a means of

controlling the well flow and connecting the well to the flow line system. Subsea trees are generally

removed when the associated well is “Plugged and Abandoned”.

Infield gathering systems include flexible pipes to gather

oil or gas from the subsea wells and route them generally to surface facilities offshore via

manifolds or directly to an onshore facility. Pipelines may be constructed from various

types of steel or composite flexible pipes manufactured from both steel and plastics. In

the case of flexible pipes their weight is generally sufficient to hold them in place on the

seabed whilst steel pipelines often require additional weight such as concrete or

mattresses to be added.

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Frequently subsea installations

have seabed gathering manifolds where simple fluid controls, metering and monitoring

equipment is located. Fluid processing and pumping/compressing on the seabed has

become technically feasible and is expected to occur more often. Manifolds are generally

lowered into place on the seabed and held by mats around the periphery or skirts on the

underside which penetrate the seabed.

Subsea controls and umbilicals distribute electrical

power and signals, and water based hydraulic control fluid to the subsea trees and

manifolds. They generally comprise of umbilical flowlines (bundled electrical cables and

steel or thermoplastic hydraulic tubing) and umbilical risers. Subsea control units

including the associated computers and distribution equipment are often located on the

manifolds or subsea trees but sometimes on separate subsea distribution units. Like

flexible flow lines, umbilicals generally have sufficient weight to remain in position after

installation.

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6. Next steps…

This information document has been provided for stakeholders interested in the decommissioning

of oil and gas infrastructure in WA. It is designed to give a brief overview of the project:

‘Independent review of the effects of decommissioning offshore infrastructure.’ It also outlines and

describes the general types of infrastructure used in WA offshore oil and gas facilities and provides

a number of generalised options for decommissioning.

It is hoped this initial information will generate discussion and can be used to share information

and raise any issues, concerns and opportunities for future decommissioning of these facilities in

WA. The questions that are generated from small groups of stakeholders will be combined with

those from other stakeholders. These questions will then feed into a large literature review process

that is endeavouring to source scientific and policy information relevant to this topic to fill any

knowledge gaps. Those areas requiring further scientific research will be prioritised as part of the

Blueprint project and used as guidance for evidence based science to inform policy and decision

making. All participants will be kept informed throughout this process and involved in the

prioritisation and review process of the project.

You are considered an important stakeholder in this process and your input is appreciated.

For further information please contact Jenny Shaw (08) 6488 4391.