Brent Field Drill Cuttings
What are drill cuttings?
Drill cuttings are pieces of rock that come out of a well, (a deep hole made in the ground, to locate oil) when a well is drilled to an oil or gas reservoir.
How to Decommission Brent: Drill Cuttings
Title: How to Decommission CUT DOWN 5 Drill Cuttings FINAL MASTER 211216
Duration: 3:35 minutes
Description:
The challenges and solutions for dealing with the drill cuttings associated with the decommissioning of the Brent platforms.
How to Decommission CUT DOWN 5 Drill Cuttings FINAL MASTER 211216 Transcript
[Background music plays]
Instrumental music with synthesised effects, at times with softer tones, at other times building to a stronger rhythm.
[Graphic]
Computer generated imagery of drill cuttings around the Alpha jacket footing at frame-left, 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.
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Drill Cuttings
[Narrator]
When Brent’s wells were drilled, a mix of lubricants was used in the drilling process, some of which were oil-based. These, and the shards of rock that came out of the wells, were discharged into the sea.
[Video footage]
Bird’s eye footage of darkened platform topsides seen against blue ocean waters. Wide footage of workers wearing safety gear surrounding a drilling rig on a platform. Low angle close-up of the rising drill rigging, with lubricants pouring down the shaft. More footage of workers surrounding the drilling rig, placing a clamp into place around the shaft.
High angle footage of an operator in the drilling control room, seated in front of a bank of screens, his hands on a joystick and other controls as he watches the screens. Underwater aerial footage of the drill cuttings on the seabed, small fish also swimming along the seabed.
Interview with Alistair Hope
[Title]
Brent Decommissioning Project Director
[Text displays]
Alistair Hope / Brent Decommissioning Project Director
[Alistair]
So around the old platforms in the North Sea, you have these things called cuttings piles, which are essentially little bits of rock and sand, but in there, there are some smaller quantities of oil based mud.
[Video footage]
Close-up of Alistair Hope as he speaks, seen against the slightly out of focus background of an office environment.
[Animated sequence]
Computer generated imagery of a gravity base structure on the seabed with cuttings piles around and on top of the storage cells. A magnified image appears at frame-right, surrounded by a yellow line and linked to the cuttings piles with a yellow line graphic. The magnified image denotes the particles which make up the cuttings piles.
Interview with Duncan Manning
[Title]
Brent Decommissioning Asset Manager
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Duncan Manning / Brent Decommissioning Asset Manager
[Duncan Manning]
The drill cuttings comprise of around 2% hydrocarbon, so very low hydrocarbon content.
[Video footage]
Close-up of Duncan Manning as he speaks, seen against the slightly out of focus background of an office environment.
[Narrator]
The practice of discharging drill cuttings ceased in the 1990s. But for existing piles, the regulator requires operators to measure the level of oil diffusing from them. If it’s below a certain threshold, they recognize that leaving the piles undisturbed is the best option.
[Video footage]
Panning front view of a platform topside seen against a background of blue seas and sky. Underwater aerial footage of the drill cuttings on the seabed, small fish also swimming along the seabed.
[Animated sequence]
Computer generated imagery of a gravity base structure on the seabed with cuttings piles around and on top of the storage cells, zooming slightly to focus on the cuttings piles.
[Alistair]
So in the case of Brent, we've got cuttings piles next to the four platforms. And, of course, in the case of the concrete platforms, there are cuttings piles on tops of the cell tops.
[Video footage]
Close-up of Alistair Hope as he speaks, seen against the slightly out of focus background of an office environment.
[Narrator]
Shell has worked with independent experts to assess Brent’s cuttings piles.
[Video footage]
Underwater aerial footage of the drill cuttings on the seabed around the base structures, small fish also swimming along the seabed.
Interview with James Blackburn
[Title]
Brent Decommissioning HSE Manager
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James Blackburn / Brent Decommissioning HSE Manager
[James Blackburn]
We have done some long-term fate modelling, to better understand what happens to those cuttings.
[Video footage]
Close-up of James Blackburn, as he speaks, seen against the slightly out of focus background of an office environment.
[James Blackburn]
And we have demonstrated that the hydrocarbon content from those original drill cuttings back in the 70’s will slowly degrade and recover.
[Video footage]
Close-up of a bearded man seated, with folded arms, at a desk and looking down, as the shot pans down, at something on the desk which is being pointed out by a hand at frame-right. Close-up of James Blackburn, as he speaks, seen against the slightly out of focus background of an office environment.
Interview with Mark Purcell
[Title]
Principal Consultant, Risk Advisory Services, DNV GL Oil and Gas
[Mark Purcell]
There’s quite a large volume of drill cuttings there.
[Video footage]
High angle close-up of diagrams on a desk, a man partially visible in rear view pointing down to the diagram with the pen in his left hand, as another hand also points in at the diagram from frame-left.
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Mark Purcell / Principal Consultant, Risk Advisory Services, DNV GL Oil and Gas
[Mark Purcell]
Our specialists looked at them, they’ve considered the environmental impacts and what was found was that at Brent Alpha and Brent Delta they were within OSPAR limits. Brent Charlie, they were fine at the seabed, but the cell tops exceed one of the OSPAR criteria in terms of the oil load released.
[Video footage]
Close-up of Mark Purcell as he speaks, seen against a glass panelled background. Rear view footage of two workers seated in front of control panels and a bank of screens in a drilling control room, cutting to a close-up in profile of the man at frame-right as he watches the displays. Close-up of Mark Purcell as he speaks, seen against a glass panelled background.
[Alistair]
The one pile that we have that is slightly above the threshold is on Brent Charlie, where there's a cuttings pile on top of the cells. So it comes up about nine metres above the cells. That one has a slightly higher leech rate of oil from it, because it's more exposed and prone.
[Video footage]
Another close-up of the diagrams on the desk and the hands pointing to them, cutting up to reveal the two men engaged in discussion, seated at the desk against the background of an open plan office environment and the large windows beyond. Close-up of Alistair Hope as he speaks, seen against the slightly out of focus background of an office environment.
[Animated sequence]
Computer generated imagery of a low angle view of the gravity base structure on the seabed with cuttings piles around and on top of the storage cells, panning slowly upwards to focus on the cuttings piles.
[Narrator]
Shell used a comparative assessment process to assess the pros and cons of managing this cuttings pile.
[Video footage]
High angle rear view footage of the man seated at the left-hand side controls in the drilling control room, his eyes on the screens facing him. Underwater aerial footage of the drill cuttings on the seabed, small fish also swimming along the seabed.
[Alistair]
If you are to remove them, it is very much using almost like a giant vacuum cleaner to suck them up onto a vessel and then bringing them onshore. So it is a big, big operation, and there is this risk of putting oil into the water column whilst you do it, that's very hard to prevent.
[Video footage]
Close-up of Alistair Hope as he speaks, seen against the slightly out of focus background of an office environment. 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. Close-up of Alistair Hope as he speaks, seen against the slightly out of focus background of an office environment.
[Narrator]
Though they exceed the threshold, removing them could worsen their environmental impact.
[Animated sequence]
Computer generated imagery of a close-up of the cuttings piles on top of the storage cells of the gravity base structure, and a pipe descending to suck up the particles, causing a cloudy release of substances at the point that the cuttings piles are being disturbed.
[Mark Purcell]
If you disturb them, the disturbance itself will create pollution and release the oil.
[Video footage]
Close-up of Mark Purcell as he speaks, seen against a glass panelled background.
[Narrator]
Shell recommends leaving all the drill cuttings undisturbed, but continuing to monitor any impact they have on the environment. This is an option the UK regulator has approved before.
[Video footage]
Footage of the display screens in the darkened control room. Aerial footage of a yellow inspection vehicle being lowered into the water. Low angle view of the inspection vehicle being lowered back onto the platform by workers wearing hardhats and safety gear. Aerial black and white footage taken as from the inspection vehicle of the platform below as the workmen reach up to guide it back into place.
[Duncan Manning]
There is a requirement to conduct a monitoring operation to understand any impact of leaving the drill cuttings in place and understand that they are degrading in line with our expectations.
[Video footage]
Close-up of Duncan Manning as he speaks, seen against the slightly out of focus background of an office environment.
[Alistair]
Northwest Hutton, which is a BP platform they've just recently revisited their cuttings pile and indeed see the cuttings piles are naturally degrading, and their environment is recovering. And in fact it's happening a bit quicker than anticipated. So, it all points to, leaving in place and allowing natural degradation, is the best way forward.
[Video footage]
High angle close-up of diagrams on a desk, a hand visible at lower frame-right pointing to parts of the diagram. Close-up of Alistair Hope as he speaks, seen against the slightly out of focus background of an office environment. Underwater panning aerial footage of cuttings piles on the seabed. Close-up of Alistair Hope as he speaks, seen against the slightly out of focus background of an office environment. More underwater footage of the seabed and the small fish swimming along it.
[Text displays]
With thanks to ROVOP / Subsea 7
[Text displays]
Shell.co.uk/BrentDecomm
The Brent Field’s equal partners are Shell UK Ltd and Esso Exploration and Production UK Ltd
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Shell jingle.
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Shell Pecten centred on a white background with text displaying below.
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© Shell International Limited 2016
During drilling, a fluid known as drilling mud is used to lubricate the drill bit and carry the drill cuttings to the surface, where they are separated from the mud and cleaned. The mud is reused where possible and the drill cuttings are either discharged or taken ashore for further treatment and disposal. When most of the wells at Brent were developed, it was standard practice to discharge the drill cuttings onto the seabed.
Drill cuttings at Brent
Drilling was carried out on the Brent Field between 1976 and 2004. Drill cuttings were discharged to sea from all four of the Brent platforms having removed the bulk of the drilling fluids. The subsequent prohibition of the discharge to the marine environment of drill cuttings contaminated with more than 1% oil by weight of oil based fluids on dry cuttings (OSPAR Decision 2000/3 on the Use of Organic Phase Drilling Fluids [OPF] and the Discharge of OPF-Contaminated Cuttings) came into force on 16 January 2001.
Notwithstanding this Decision, we had already stopped discharging drill cuttings contaminated with OPF to sea in 1998. Following this, the arrival of new processing equipment on the market which could clean contaminated drill cuttings to the required standards of OSPAR Decision 2000/3 caused a revision of the internal Shell requirements and we began to discharge (under permit) drill cuttings contaminated with OPF in line with the OSPAR Decision.
As well as on the seabed, drill cuttings have settled on top of, and between, some of the oil storage cells that form part of the three gravity base structures (GBS).
The drill cuttings have been surveyed and sampled regularly since the late 1990s, most recently in 2015. Using our drilling records and the data from these surveys, we estimate that there are around 18,752 cubic metres (m3) of drill cuttings on the seafloor at Brent, and about 13,412m3 on the cell tops.
What do the regulations say?
Regulations governing the disposal of oil-based drill cuttings in the North Sea came into effect as a result of the OSPAR Decision 2000/3 (as mentioned above), the regulations prohibit the discharge of oil-based drill cuttings containing more than 1% oil by weight of dry cuttings.
In 2006, a second regulation came into force due to OSPAR Recommendation 2006/5, which requires drill cutting piles to be assessed to confirm that the impacts of pollution by oil and/or other substances from cuttings piles are reduced to a level that is not significant. OSPAR 2006/5 also recommends that for cuttings piles which fall below the two thresholds, no further action is necessary. http://www.ospar.org
What is our decommissioning recommendation?
Over the decades, our sampling and modelling has consistently shown that all the seabed drill cuttings piles at Brent and the cell top drill cuttings at Brent Delta and Bravo are below the OSPAR thresholds. Our long-term fate modelling analysis predicts that this will not change over the next 1,000 years. As none of these drill cuttings piles exceed the OSPAR thresholds, our decommissioning recommendation is to follow the advice of OSPAR and leave them in place to degrade naturally.
Brent Charlie cell top cuttings
Analysis of more recent samples from the Brent Charlie cell top cuttings pile, and the revised long-term fate modelling using new data from these samples, indicated an oil leach rate which slightly exceeds the OSPAR threshold.
In line with the OSPAR Recommendation for cuttings that exceed the threshold, we carried out a stage 2 Comparative Assessment to compare a number of options to handle these, including leaving them in place. As a result of this Comparative Assessment, our decommissioning recommendation is leave these drill cuttings in place to degrade naturally to avoid disturbing the drill cuttings in the water column.
What if the drill cuttings need to be disturbed?
It is possible that the drill cuttings pile under the steel jacket of Brent Alpha may be disturbed when the jacket is decommissioned. Similarly, some of the drill cuttings piles on the cell tops of the three GBS may be disturbed if we are required to gain access to the top of the cells or during other required decommissioning activities, for example small quantities on Brent Delta have been water jetted under permit to enable attic oil operations to be carried out.
We have carried out comparative assessments to identify recommended decommissioning options for the drill cuttings piles at Brent Alpha and on the cell tops if they need to be disturbed as part of the decommissioning process.
Our recommended option for Brent Alpha seabed drill cuttings piles is to leave them in place to degrade naturally alongside the footings of the steel jacket. For the Bravo and Delta cell tops our recommended option is either to water-jet them onto the seabed if only small quantities need to be disturbed, or remove them and treat them onshore if larger quantities need to be disturbed. For Brent Charlie, the recommended option is to remove the drill cuttings and treat them onshore if the cell-top pile needs to be disturbed.
Monitoring and Liability
After decommissioning we will discuss and agree with the Department for Business, Energy and Industrial Strategy (BEIS), a long term monitoring programme for the drill cuttings.
Shell and Esso will remain liable for any remaining facilities, pipelines and drill cuttings after decommissioning the Brent Field, in accordance with applicable legislation.
More in Brent Field Decommissioning
Brent Field Recommendations
Learn more about the Brent Field recommendations
Brent Field Gravity Base Structures
Decommissioning the GBS