A to Z of Engineering: Oil Rigs

Welcome to Engineer Academy where we’re exploring an A to Z of Engineering – everything from acoustics to zoos.

In each episode, we spin the wheel to find out what type of engineering we’ll be exploring with the help of Engers, our engineering expert.

You can listen to the full series of the A to Z of Engineering here.

Let’s take a look at the engineering behind oil rigs!

Oil is used to power our cars, but the oil doesn’t magically appear in petrol pumps. Engineers have designed oil rigs which can pump oil from under the sea, and it’s no easy task.

Welcome to The Engineer Academy, where we’re exploring an A to Z of everything engineering from acoustics to zoos.

In each episode we spin the wheel to find out what type of engineering we will be doing with Engers, our engineering expert.

Oil Rig Engineering

We use energy every day in our homes, schools and businesses. You probably know that it comes from a number of different sources – including oil and gas as well as renewable sources such as wind, hydro and solar.

Oil is found deep underground – and that can be anywhere… from deserts to the oceans. Now while it can be a challenge to extract oil on land, it’s even more of a challenge at sea – when the winds can blow at 60 mph. To safely drill for oil at seas, massive structures called Offshore Oil Rigs are used.

One of Britain’s most well known oil fields is the Brent Oil Field in the North Sea – 186 kms north-east of the Shetland Islands. It was developed in the 1970s with four gigantic oil platforms – called Alpha, Bravo, Charlie and Delta helping to provide our country with energy for over 40 years. At peak production, the Brent Field was producing over 800,000 barrels of oil per day – and a massive 25.5 million cubic metres of gas. Amazingly it took just 7 years from design to start drilling for oil and was all fully up and running by 1981. But what happens when an oil rig comes to the end of its life?

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Brent Delta came to the end of its working life in 2011, Brent Alpha and Bravo ended production in 2014 when the field became depleted, and Brent Charlie finally shut down in 2021. The next stage was for the platforms to be decommissioned – which means taken apart and recycled.

Each of the Brent platforms was a whopping 300 metres tall from seabed to the top of the structures – that’s taller than the Eiffel Tower! They had a platform deck as large as a football pitch – and weighed the same as 2,000 London buses. So… how do you dismantle something so big?

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The main part of an oil rig is called the topside, which is kept steady on top of strong legs which reach over 140 metres down to the seabed. Three of the four rigs had concrete legs, whilst Alpha had steel lattice legs.

Once production stopped and no more oil or gas was being pumped, the first thing to be done was to clean and seal up the wells so no oil or gas could escape into the sea around the rigs. This is a process called plug and abandonment – and can take a bit of time – especially with over 140 wells to be plugged.

Once plugged, engineers could then move up to the topside – the main part of the structure. This could be decommissioned by dismantling it onsite or by cutting it into pieces and floating them away on barges. Shell decided to remove Brent Delta in one piece.

Before anything could be lifted away, the topside had to be separated from its support structure. On the rigs with concrete bases, cuts were made from inside the bases. On Alpha, engineers had to abseil down to cut the steel lattices with blow torches. As you can imagine this was VERY dangerous work – and not for the faint hearted!

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Now, you might be wondering, with all the wind and waves in the North Sea, why don’t the rigs collapse into the sea when those cuts were being made? Part of the clever engineering was using castellated cuts – instead of going straight around, engineers made cuts in the shape of turrets like on a castle. This helped keep everything in place.

After 5 years of planning, everything was in place for the great lift. But how do you lift something that big in the North Sea?

Let me introduce Pioneering Spirit – a special twin hulled construction vessel. It looks a bit like 2 ships welded together side to side but with a huge gap – the width of an oil rig in between. It straddles the platform and using 16 hydraulic lifting arms, can lift the topside in a matter of seconds. It’s ENORMOUS! At 382 metres, it’s as long as 6 jumbo jets, and can lift 48,000 tonnes!

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Once lifted, Pioneering Spirit carried the platform back to the UK where it was broken down into small pieces and recycled. Amazingly. 97% of the rig could be used again. The supporting legs were left in the sea where they stood – becoming a permanent home to sealife.

Work to dismantle Alpha Bravo and Delta is now complete – with Charlie’s decommissioning set to be complete by 2025. These incredible structures were part of our energy history and the process of putting them to bed has been historic too.

And that’s our take on the letter O – it’s been OUTSTANDING!

If you would like to check out some other types of engineering, why not check out Optical, Organic, Operations or Operations engineering!

Join us again next time to spin the wheel and explore another letter in the A to Z of Engineering!