The drilling challenge

We are addicted to oil: we consume about 30,000,000,000 barrels of it per year (a volume of 4.8 cubic kilometres). The problem is that it's getting harder and harder to find. Back in the 19th century there were places in the world where it just oozed naturally out of the ground. If you wanted an oil well, all you had to do is pick up your shovel and dig a hole! Those days are long gone. Now we have to drill for oil in more and more hostile places like the deserts of Africa and the frozen arctic wastes of Alaska.

Keep on drilling...and drilling...

Drilling for oil in these places is quite risky as it's possible to hit an overpressure at any time.


That blows - literally!

An overpressure is a high-pressured pocket of oil or gas. The pressure can be so high that it can squirt the drill pipe clean out of the hole with enough force to take the whole drilling rig with it. This is known as a blow out and can be a bit unnerving to say the least.

To stop this happening, a very dense mixture of heavy minerals known as mud is poured into the hole. The weight of the mud provides a massive pressure designed to balance the pressure of the oil or gas pushing upwards. This is usually enough to contain it. If it isn't the next, and often the last, line of defence is the blowout preventer (BOP).

Bop it!

The BOP is a giant stack of 'shut-off valves' that close if the weight of the mud cannot contain the over pressure. They can be huge structures weighing up to 500 tonnes. If they're working properly, giant hydraulic rams seal the well a few seconds later.

The drilling challenge!

As oil gets scarcer and more valuable, oil companies are drilling in even more challenging environments such as the deep ocean. This is the most challenging of all. Britain pioneered ocean drilling back in the 1970s. The off shore fields of the North Sea still provide Britain with a thousand million barrels of oil per year.

Back then drilling in 300ft of water needed all the technology and expertise Britain could throw at it. Even today it's still not an easy environment to work in. Some of the largest and most elaborate structures made by man are oil platforms working in the North Sea. Back then it was easy peasy compared to where oil companies are working now.

In the Gulf of Mexico rigs are drilling in seas over 5000ft deep. That's a mile of water before you even start drilling into the earth! So how do the engineers get the blow out preventers past all that water in time? They have to be on the sea bed on these rigs. At this depth, the environment is more hostile than even the surface of the moon.

Why is it so hostile down there?

  • The pressure that deep down under the water is 147 times more than what it is at the surface
  • No human divers can operate there, the pressure is lethal
  • Only remote controlled submarines can survive
  • It is pitch black that deep underwater
  • No light can penetrate that far
  • It is really cold down there. Very icy waters!


So what happens when things go wrong?

The Deepwater Horizon rig in the Gulf of Mexico was all over the headlines because it hit an overpressure and the weight of the mud could not contain it. But that's not all. What else happened?

  • The BOPs failed
  • A supersonic blast of oil and gas raged up the hole expanding and accelerating all the time
  • The explosion and fire that happened killed 11 people
  • It started one of the worst oil spills in history

The question everyone's asking is, why did the BOPs fail?

How was the leak stopped?

This is the 64 billion dollar question. The key to understanding why it was so hard to plug the leak is to appreciate how hostile it is down there. No one seems to have contemplated the prospect of catastrophic failure with a rig operating in such deep water. It was very difficult to control the leak because the end of the riser pipe that is used to go from the BOP on the sea bed to rig on the surface was 5000ft underwater and gushed about 200,000 gallons of crude oil into the sea every day.

First...slow the leak down

The first attempt to slow down the leak was to prop an enormous steel and concrete funnel over the main leak and channel the oil up a pipe to the surface where it could be pumped into a tanker and taken to shore. But that didn't work. The very low temperature of the water at that depth caused the oil to congeal into a kind of frozen sludge that simply blocked the funnel.

What else was done?

The next attempt involved feeding a new tube into the old pipe and pumping in a goopy mixture of old tyres and concrete to try and block the pipe. This also failed.


What next?

The final option was to drill a relief well. It was a long drawn out, very difficult job. To succeed in doing this engineers dropped 5000 feet of drill string down to the sea bed. Then they drilled a further 18,000ft through solid rock. Finally, they drilled sideways into a target pipe a few metres across. Easy.


This took around three months. An awful lot of oil found its way into the environment by that time and the Deepwater Horizon spill ended up being the largest acciedental marine oil spill in the history of the petroleum industry. The effect on the nearby marine habitats and the Gulf of Mexico's fishing and tourism industries was devastating.