FoundOcean – Brent Bravo Decommissioning
Our Managing Director, Jim Bell, talks about one of a growing number of decommissioning projects as we see some of our North Sea oil and gas field production cycles come to an end.
Why is decommissioning important?
Decommissioning is a growing trend in the oil and gas industry, in fact, it is becoming a significant industry in its own right. Several of the oil and gas fields in the North Sea are reaching the end of their life cycles, and it is important that they are decommissioned carefully.
So far only 12% of structures in the North Sea have been decommissioned, so the scope for growth in this type of project is huge. In order to stay in line with the requirements of regulators, and considering the environmental impact of the process, the removal of structures and plugging of wells needs to be thoughtfully planned and executed. Two key regulators are the UK body OPRED (Offshore Petroleum Regulator for Environment and Decommissioning) and OSPAR (15 governments controlling the western coasts of Europe, together with the European Union) and, over the next 25 years, £30 billion is expected to be invested in decommissioning projects in order to meet their requirements.
Typically, the first stage in the process involves plugging the oil wells themselves, known as “plug and abandon” or P&A. Following that vitally important step, the structures above need to be removed, in most instances fully removed back to the seabed. In some cases, however, the structures are decontaminated and left as artificial islands or reefs to encourage marine life.
The Brent Field, situated in the North Sea near the Shetland Islands, was one of the largest oil and gas fields in the UK, brought into production in 1976 and reaching the end of its life cycle in 2006, when all production ceased and it was assigned for decommissioning.
The Brent Field was made up of four platforms: Alpha, Bravo, Charlie and Delta. The latter three platforms were Gravity Base Structures (GBS), a particularly robust structure made of one or more concrete legs, designed to withstand the stormy conditions in the North Sea, making the decommissioning work particularly challenging. The decommissioning project was of a significant scale as the Brent Field was one of the largest in the UK, and had to be approached carefully so as to minimise any environmental impact to the surrounding area.
Each of the three Gravity Base Structures at Bravo, Charlie and Delta, weighed approximately the same as the Empire State Building, a mighty 300,000 tonnes. The topside platforms alone were 25,000 tonnes and had to be removed from the concrete legs to be floated ashore for recycling. The first platform to be dismantled was Brent Delta, a decommissioning project that reached completion in 2017.
FoundOcean and Brent Bravo
Following the successful decommissioning of Brent Delta, Brent Bravo was subsequently decommissioned in 2017, a project in which FoundOcean played a significant part. Lessons had been learned from the Delta decommissioning, meaning that the Bravo project was completed both under budget and ahead of schedule. The process was streamlined to provide a 70% reduction in preparation work. The learnings from the earlier project and subsequent planning for this one meant that there was a much-reduced requirement for work offshore, resulting in a safer and simpler task for Brent Bravo’s decommissioning.
FoundOcean’s expertise in delivering custom projects had a hugely positive impact on this process. We developed a special concrete blend to construct six reinforced concrete blocks that supported the topside lifting of the platform. We conducted a series of trials onshore in order to create the grout mix and find the correct hydration temperature, strength and density. Our analysis proved the concept for the grout and addressed ‘heat of hydration’ concerns for the large pour dimensions that were required. FoundOcean also designed and installed a modular shuttering system for the lifting block formworks, and installed and fixed the reinforcement within the cramped confines of the topside’s labyrinthine rooms and corridors. Ultimately, the entire platform was removed in a single 9-second lift by Allseas’ Pioneering Spirit, in order to be transported onshore for recycling. The Brent Bravo topside had been constructed with stability in mind and the platform was never originally designed to be lifted from underneath. Achieving this as a single lift was an amazing feat of engineering.
During the Brent Bravo decommissioning project, we mixed more than 800 tonnes of dry grout material in a large super pan mixer whilst offshore. This required efficient logistical planning and communication in order to take into account the supply vessel capacity, weather conditions and the offshore throughput of grout. We arranged for the big bags of pre-blended grout to be delivered by road to Aberdeen and then immediately shipped onwards offshore, a significant collaboration between our FoundOcean team and other contractors working on the project, demonstrating our commitment to communication and teamwork.
Our successful involvement in this project has paved the way for a significant amount of ongoing decommissioning work, including other Brent field platforms in 2019 and further North Sea projects in 2020 and 2021, allowing us to develop our expertise in the growing field of decommissioning.
There is a fantastic short film on YouTube of the Brent Bravo project, called ‘There We Go’ – Lifting 25,000 tonnes in 9 seconds. Take a look!
For more information on FoundOcean’s experience and capabilities, contact the team on +44 1506 440330 or email email@example.com.
[image courtesy of AquaTerra - 01224 392626 | www.aquaterra.co.uk]