Brent Field Pipelines
Brent is one of the largest UK oil and gas fields ever developed. Its pipeline system is extensive, connecting the four platforms used to develop the field to the subsea production facilities and to pipelines that transport oil and gas from Brent and from other fields to onshore terminals in Scotland.
How to Decommission Brent: Pipelines
Title: How to Decommission Brent Field Pipelines
Duration: 3:16 minutes
The challenges and solutions for decommissioning of the pipelines in the Brent oil and gas field.
How to Decommission Brent Field Pipelines
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Instrumental music with synthesised effects, at times with softer tones and at other times building to a stronger rhythm.
Computer generated imagery of the outline of a gravity base structure at frame-left with a pipeline extending towards frame-right, seen against a dark greenish background with lighter streaks descending from top of frame representing rays of light piercing the dark underwater environment, the shadows and sunlight dappling the seabed.
The Brent oil and gas field is one of the largest ever developed in the UK.
Bird’s eye view of one of the Brent platforms and a vessel alongside, seen against the background of a glistening ocean and an evening sky. Wide view of the four Brent platforms and a vessel against a background of grey seas and skies.
Its pipelines connect the four Brent platforms to subsea production facilities…
Computer generated imagery as though from space of the UK surrounded by sea and other continents, zooming in to mark the Brent oil field with a yellow square and then yellow dots appear, marking the location of the four Brent platforms and pipelines.
Brent Oil Field
Delta / Charlie / Bravo / Alpha
…and they transport oil and gas from Brent and other fields, to terminals on shore.
Close-up panning footage of pipeline inspection with inspection data displaying at the top of frame. Wide view of an onshore terminal against a background of blue skies. Aerial footage of an onshore terminal with the ocean visible in the background.
There are 103 km of pipelines across the Brent Field. They vary in length from 300 metres, to 36 kilometres.
Underwater extreme close-up of a section of pipeline surrounded with algae, barnacles and other marine life. High angle footage of a subsea pipeline being laid off the back of a pipelaying vessel.
Interview with Duncan Manning
Brent Decommissioning Asset Manager
There’s 28 different pipelines in the Brent Field that we are looking at for decommissioning.
Rear view close-up of Alistair Hope pointing with his pen to an infographic on a page that he is holding up at eye level, before lowering the page.
Duncan Manning / Brent Decommissioning Asset Manager
These vary in size from, kind of, three inches up to over 30 inches in diameter.
Close-up of Duncan Manning as he speaks, seen against the slightly out of focus background of an office environment.
Interview with Alistair Hope
Brent Decommissioning Project Director
For the very big lines…
High angle close-up of the open ends of two very large pipe segments alongside one another.
Alistair Hope / Brent Decommissioning Project Director
…24 inches in diameter, that sort of scale, often they’re concrete coated to keep them on the seabed.
Close-up of Alistair Hope as he speaks, seen against the slightly out of focus background of an office environment. High angle view of pipe segments stacked alongside and on top of one another while more are hoisted over and lowered to join them.
Concrete coating is used to protect pipes and ensure they meet their planned life expectancy.
Wide footage of the concrete weight coating process. A man covers a pipe with mesh reinforcement. The pipe then moves through a machine process where it is coated in concrete.
Some of them are rigid steel pipes, some of them are more like flexible hoses in fact. And some of them are buried, some of them are laid on the seabed. A collection of different lines used for different purposes.
Wide panning footage of pipes aboard a vessel, blue sea and sky in the background; again, a tower crane is hoisting a section of pipe and moving it into place. Extreme wide footage of pipe being laid along the ground and partially buried, several men moving about the site. Close-up of Alistair Hope as he speaks, seen against the slightly out of focus background of an office environment. Underwater close-up of a section of pipeline on the sea bed, surrounded with algae, fish and other marine life.
The first step in decommissioning is to clear the inside of all the lines.
Computer generated imagery of a pipeline along a cross section of seabed, showing the pipeline filling with blue as it is flushed.
In all cases we would be flushing the lines so that they don’t contain anything undesirable.
Close-up of Alistair Hope as he speaks, seen against the slightly out of focus background of an office environment. Footage inside a pipeline as impurities are flushed through.
Each pipeline has been individually assessed, to establish the most appropriate decommissioning method currently available.
Wide footage of James Blackburn and other colleagues seated alongside each other at a long table in a conference room, their attentions on the laptop screens in front of them. This cuts to a close-up of the female colleague at the furthest end of the table. Close-up of James’ fingers tapping on the keys of his laptop, and panning up to a close-up in profile of his face, his colleagues faces forming part of the out-of-focus background.
Each pipeline is slightly different and each pipeline needs to be looked at individually.
Close-up of Duncan Manning as he speaks, seen against the slightly out of focus background of an office environment.
Where pipelines lay inside trenching, or have had piles of rock spread on top of them, Shell is proposing they are left undisturbed.
Computer generated imagery of the pipeline along a cross section of seabed, the pipeline still shaded in blue. Rocks fall from top of frame to cover the pipeline.
Aerial footage of the seabed, fish swimming about in all directions.
If a line isn't a hazard to other users of the sea, is it really worth pulling it up? Because actually, in some cases, you are disturbing the seabed again, to pull them up.
Close-up of Alistair Hope as he speaks, seen against the slightly out of focus background of an office environment. High angle underwater footage of a section of pipeline along the seabed, showing algae attached to the pipeline and fish swimming around the line. Again, a close-up of Alistair Hope as he speaks.
Where it makes sense, some pipelines will be removed.
Low angle underwater footage of a section of pipeline, fish swimming alongside the pipeline.
Computer generated imagery of the pipeline along a cross section of seabed, the pipeline slowly lifting up off the surface of the seabed and being pulled to the surface.
It tends to be that the smaller lines are relatively easy to reverse reel, so the flexible lines, the umbilical type lines, those are relatively easy to remove and we would remove them.
Close-up of Alistair Hope as he speaks, seen against the slightly out of focus background of an office environment. Bird’s eye footage of a large pipelaying vessel against the background of blue seas and skies. Close-ups of flexible pipelines being reverse reeled back up onto the vessel. Again, a close-up of Alistair Hope as he speaks.
The team is proposing that some pipelines are trenched and buried, that some other pipelines, or parts of them, remain on the sea-floor and, where necessary, any exposed ends will be covered by rock so they don’t pose a snagging risk to fishermen.
Footage of a bank of screens showing underwater footage and data. The footage pans towards frame-right to show a man at the controls and facing the screens. Aerial footage of a section of pipeline surrounded by algae and swimming fish. Low angle close-up of a section of pipeline with a fish swimming alongside. Vertically panning footage aboard a fishing vessel, grey seas and skies forming the background.
I’ve personally engaged closely with the Scottish Fishermen’s Federation to ensure that we understand any impact of anything which is being left behind, on the fishing activity in that area.
Continuing footage aboard the fishing vessel, grey seas and skies forming the background. Close-up of Duncan Manning as he speaks, seen against the slightly out of focus background of an office environment. Footage of the fishing vessel moving through grey waters, as from the point of view of port side, with land visible in the distance. Footage of a man uncoiling a rope on the deck of the vessel.
Interview with Bertie Armstrong
Chief Executive, Scottish Fishermen’s Federation
Bertie Armstrong / Chief Executive, Scottish Fishermen’s Federation
Living with pipelines has been a feature of our life for the last 50 years.
Close-up of Bertie Armstrong as he speaks, seen against an out of focus background of an office environment.
If a pipeline is trenched and buried and has been for its life, then often the removal of it causes more problems than leaving it there.
High angle close-up footage panning the length of an underwater pipeline that is covered in algae. More underwater aerial footage of a pipeline surrounded by swimming fish and marine life.
Shell would ensure any permitted lines remaining, are all marked on maritime charts and on the fishermen’s GPS database, FishSafe, so that vessels are able to see them and avoid any problems.
Low angle mid view of a man holding up a tablet device. Close-up of the screen as the man navigates it with his fingers. Footage of the man reaching out to press buttons on one of the display screens on the bridge. Close-up of the screen displaying maps with symbols and lines that chart the offshore surface and subsea oil and gas structures. Panning footage of the seabed showing different types of fish swimming in all directions; inspection data displays at the top of frame.
Advances in technology may open different decommissioning opportunities, which can be considered in the future.
More underwater aerial footage of a pipeline surrounded by algae, small fish and marine life. Close-up panning footage of pipeline inspection with inspection data displaying at the bottom of frame. Footage of a wave breaking over a rock outcropping.
With thanks to AVC Media Enterprises / Subsea 7
The Brent Field’s equal partners are Shell UK Ltd and Esso Exploration and Production UK Ltd
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© Shell International Limited 2016
There are 28 pipelines and umbilicals (including one power cable) to be decommissioned at Brent. They measure approximately 103km in length, with the shortest being just 0.03km and the longest 35.9km. They are grouped into four different categories:
Rigid pipelines are generally used to transport oil or gas to shore. They are usually made of steel, coated in a layer of concrete to provide stability. By the very nature of these materials, the pipelines are rigid.
Flexible pipelines are made of steel, plastic or various composite materials. They have small or medium diameters and are mostly used for shorter lengths of pipeline.
Umbilicals are typically used to inject chemicals into, or transmit control signals to, the subsea production system. They are usually of small diameter and pliable structure, similar to those of flexible pipelines.
Power cables provide electricity for the subsea system. They are similar to umbilicals but contain large electrical cores.
What do the regulations say about pipeline decommissioning?
The main legislation in the UK covering pipeline decommissioning is the Petroleum Act 1998 and the Pipeline Safety Regulations 1996. There are no international guidelines on pipeline decommissioning.
The UK Department for Business, Energy and Industrial Strategy (BEIS) has issued Guidance Notes on Decommissioning which include the decommissioning of pipelines. These require each pipeline to be assessed individually and you will be able to find full details of the recommendations for each of the Brent pipelines in the Pipelines Technical Document when the Decommissioning Programme for the field is submitted.
If a pipeline cannot be re-used, all feasible decommissioning options should be considered and a Comparative Assessment (CA) made to arrive at the recommended option. Every pipeline in the Brent Field will therefore be subject to an individual CA.
Each pipeline will be flushed
As part of the decommissioning process, the pipelines will be flushed and pigged (the process of passing a mechanical device through a pipeline to scrape the inner surfaces) where appropriate, to remove any remaining oil, gas, wax and other contaminants. The waste will be collected at the receiving platform in tanks and transported to shore for treatment and disposal.
What are the decommissioning options for pipelines?
We have identified 14 pipelines where the decommissioning options are simple and straightforward, and the solution more obvious based on the BEIS Guidance Notes. The relatively fewer, simple decommissioning options for these lines were compared and assessed using a qualitative or narrative-based method. For simplicity, we refer to these as “qualitative” pipelines.
For the other 14 pipelines, the options are more numerous and complex, with no preferred decommissioning option being immediately apparent. We have called these “quantitative” pipelines since we subjected each of them to comparison and assessment using a quantitative method. This approach is consistent with the expectations of the regulator.
For qualitative pipelines there are two groups of decommissioning options:
- Leave the pipeline in place in its existing trench or under the existing rock dump, with any protruding end removed and/or covered with rock to reduce the risk of snagging by vessels; or
- Remove the line completely, either by reverse installation or cut and lift.
For quantitative pipelines we identified nine technically feasible options, although not every option was applicable to each pipeline. These include:
- Leave tied in at both ends;
- Leave tied in at platforms, trench and backfill remote end;
- Leave tied in at platform, rockdump remote end;
- Trench and backfill whole length;
- Rockdump whole length;
- Recover whole length by cut and lift;
- Recover whole length by reverse S-lay (where the pipeline is taken aboard a vessel and cut into smaller sections for transportation to shore);
- Partial trench, backfill and isolated rockdump; and
- Partial rockdump
Comparative assessments and many studies
We have carried out a separate CA of each of the 28 Brent pipelines. Each assessment considered the construction, condition and position of the pipeline and the feasible decommissioning options.
In accordance with BEIS guidelines we examined each decommissioning option in terms of five criteria: technical feasibility, effects on society, environmental impact, risk to safety, and cost.
The CAs were informed by a number of studies that were either carried out by ourselves or commissioned from independent experts, for example: Anatec, which carried out a study of safety risk to other users of the sea; Mackay Consultants, which looked at the socioeconomic effects on leaving equipment behind on fisheries; and Atkins, which worked on pipeline degradation. These included a pipeline degradation assessment, an assessment of the safety risk to fishermen, a soil and trenching analysis, a rock-dumping assessment, and an environmental impact assessment.
What do our comparative assessments recommend?
Most decommissioning options involve a balanced judgement between two or more BEIS criteria. In the case of the pipelines, most of the balanced judgements are between technical feasibility and/or cost on the one hand and the long-term safety risk/long-term environmental impact on the other.
The 14 simpler, qualitative pipelines include all the flexible lines, umbilicals and the electrical cable, as well as four rigid pipelines. Our recommended options are to remove nine of these pipelines and leave five in place - in one case under rocks.
The 14 more complex pipelines are all rigid. We recommend that 13 of these remain in place as is on the seabed, with the other one to be left on the seabed after being retrenched.
All the lines included in the Decommissioning Programme are intra-field pipelines, and critical infrastructure in the form of the main gas and oil export pipelines will remain. Bypass plans have been put in place to support production from other fields post decommissioning.
Are the pipelines a risk?
An important criterion for all the decommissioning options is the level of risk they present to other users of the sea, especially fishermen.
There is currently a 500 metre exclusion zone around each Brent platform, which will continue to apply after decommissioning is completed. The platform legs and the pipelines will be clearly marked on all relevant sea charts, and will be logged in the FishSAFE database, which warns fishermen about snagging hazards in UK waters.
Currently, the exposed sections of pipelines are crossed regularly and safely by bottom-trawling fishing gear. To assess the risk of whether pipelines could present a potential snagging hazard when they degrade, we commissioned two studies: one to quantify the extent of fishing along each Brent pipeline and the speed and angle of the vessels crossing it, and the other to assess the long-term degradation of each pipeline.
These studies have informed our CA and recommended options. We have held frequent meetings with fishing and marine authorities and fishermen’s associations to present our findings and receive their input.
Who is responsible for Brent after decommissioning?
Shell U.K. Limited and Esso Exploration and Production UK Limited are the joint equal owners of the Brent field. Under current legislation both companies will be responsible for inspecting and monitoring the pipelines after decommissioning.