Credit: RobEllis

Shell has invested heavily in alleviating stakeholder concerns over toxic waste management during the planned decommissioning of its Brent field, learning from the controversy created ahead of its 1995 Brent Spar removal.
The Brent field was installed in the mid-1970s and 99.5% of the economically recoverable reserves have been obtained.
The decommissioning of the field is posing a new set of challenges and opportunities to the energy sector and its supply chain.
“From Shell’s perspective it’s the largest decommissioning project we’ve ever done. The technology at the heart of the platforms no longer exists … and when it was put in place, decommissioning wasn’t at the front of people’s minds – it was all about getting hydrocarbons out of the ground,” Manning said in an interview.
The Brent field has 103 km of pipelines, 140 wells, and 64 oil storage tanks. The hubs were provided by four immense platforms, Alpha, Bravo, Charlie and Delta, of which Charlie is the only one still producing oil. Alpha and Bravo ceased operation last year and Delta stopped work in 2011.
The 300,000 tonne dilemma
Shell has been working for almost 10 years on its decommissioning plans, and the high cost Plugging & Abandonment work is already well advanced.
All the wells for Delta have been plugged and their conductors are currently being removed. Work on P&Aing Bravo is half completed and Shell plans to start work on the Alpha wells shortly. A tougher test of Shell’s engineering and public relations skills will be dealing with the platforms.
The removal of the topsides is relatively straightforward on a regulatory and engineering level, but the real issue is the gravity base structures (GBSs) that ballast Bravo, Charlie and Delta. These weigh about 300,000 tonnes and contain large oil storage “cells.”
These structures present a challenge in the light of the 1995 Brent Spar debacle.
Like Brent Spar, the GBSs contain toxic waste, but whereas the Spar was a floating structure, and therefore easy to tow, the bases of the Brent field platform are designed to be more or less impossible to move.
“When you consider the weight that we have to take out of the water – the cells and the legs are more than a meter thick of heavily reinforced concrete – they provide us some very real engineering challenges that we’ve had to really focus on,” Manning said.
“We’ve studied whether it’s possible to refloat these structures and we haven’t completely bottomed that out, but the challenges associated with refloating – bearing in mind that they weren’t designed with refloat in mind – are very, very considerable - with very large risks attached,” he said.
One issue is the closing of the conductor and other openings, an operation that has to be performed by remotely operated vehicles. If the openings are not sealed, it is not possible to create the necessary pressure within the skirts to free the base from the seabed.
Given the mass of the GBS, it would be difficult to control its momentum when it is broken free from the grouting that holds it to the sea bed. In particular, it would be difficult to predict all of the forces involved.
Worst case scenario
Ofspar regulations operate a “clean seas” policy, which requires that all oil infrastructure be removed. Operators are allowed to seek a derogation from this rule for steel structures heavier than 10,000 tonnes, very large concrete structures and operations that carry an unacceptable safety risk.
The size of the structure entitles Shell to derogate on the Ofspar Clean Sea regulations, and the removal of the bases would represent a huge cost, but the company has had to bear in mind that it was Greenpeace’s claims about the residue in the Brent Spar oil cells that mobilized public opinion.
Following a three-month drilling operation, Shell has recovered samples from a number of layers of liquid and sludge in the cells, and is presently studying them in its laboratories.
“With Brent Spar in mind, there is a lot of focus on understanding what is the best, most appropriate solution for these platforms,” Manning said.
Under the current regulatory scheme, Shell must carry out a “comparative assessment process to confirm that leaving them in place is the most appropriate solution,” he said.
Under the regulations, there are five criteria to be applied.
“We have to strike a balance between engineering feasibility, impact on the environment, impact on society, cost and, of course, safety. We have to make a decision based on these five often competing factors,” Manning said.
The toxicity of the cells does “not necessarily” require removal of the GBS units, Manning said.
Shell could theoretically attempt a removal of the GBS, but “It’s a challenge of a different scale to removing the topsides, and it’s never been done before…It’s an option we really have to bottom out.”
Stakeholder dialogue
One lesson that Shell has learned from Brent Spar is the need to consult stakeholders early on. These stakeholders include local and national governments, industry bodies, academics, fishing associations, community groups and trade unions, as well as environmental groups.
Shell has consulted no fewer than 180 groups since 2007. In 1995, by contrast, the company obtained the support of the UK government, but made little attempt to explain itself to the wider public.
“In the engagement process, the contents of the cells is clearly one of those issues that has been a particular focus from a stakeholder perspective,” he says. “We’ve generated our own cell management stakeholder task group to focus on this issue - and the first part of that was understanding the nature of the sediment, so it required a real focus from us to get samples.”
Shell is continuing to study the quantity and composition of these samples and then engage stakeholders to identify the best solution based on the five comparative assessment criteria that have been presented by the regulators.
The firm’s approach to engineering and consultation will be a reference point for the rest of the industry as it gets to grips with large-scale decommissioning and the cell sampling research has not been conducted before.
Shell completed a public consultation on the Delta topside removal plan on March 21. An independent laboratory is currently performing chemical and physical analyses on the cell samples and Shell is running the results through a modelling system created to assess them against the five decommissioning criteria. Once this is complete, the preferred option will be identified and presented in the main Decommissioning Program.
Strengthening the supply chain
The Brent field project will spur British industry to acquire the required expertise and equipment to become a global player in the decommissioning of oil fields, Manning said. “We’re not the first to decommission, but we’re at the forefront of what we’re doing. From a UK perspective, it will provide a real opportunity to be on the front foot and develop this emerging supply chain. The Gulf of Mexico is slightly ahead of us, but we sit in a mature regulatory regime so therefore we have very stringent standards and the capabilities that are being developed here in the UK are likely to be world-leading, and will allow us to lead this emerging subsector for 10 and 20 years. It’s a really exciting time.”
Manning called for further efficiency improvements in the Plugging & Abandonment process, which could benefit the decommissioning sector globally.
“It’s such a large component of the cost that revolutionary and evolutionary technology that would drive the more efficient delivery of plugging would have massive benefits for everyone. “