Did you realise that we have a big hole in the bottom of our boat? Its hard to imagine that a boat can float with a hole in its bottom, but there has to be somewhere for the drill string to pass from the derrick to the sea floor. This big hole is called the moon pool and on rare occasions like the other day, we get to see the moon pool completely open. Here I talk about why we had the moon pool opened up and what happens when we have to change a drill bit.
Drill bits don’t last forever. They like to get changed after around 60 hours, or around 150-200 m worth of drilling. If they don’t, there is a chance that the drill bit will break up during drilling and then we have to use a special drill bit to get through the chunks of metal that will be left in our hole! So, at around 145 m depth we stopped drilling. But, to change the drill bit we have to retrieve the entire drill string to the ship. How do we find the hole again with a fresh bit? Remember, the hole is under 2000 m of sea!
To make finding the hole easier, the drillers deploy what they call a free fall funnel. You’ll see why its called ‘free fall’ in the video at the end of this blog. The funnel is a giant metal funnel that is painted like a target on the inside, with the site number written in big letters. This is sent down the drill string when we are ready to come out of the hole. That way, when we want to find our hole again, we have a big target to look for and a big funnel to guide the drill bit.
The funnel is a few meters wide, so it needs a lot of space when it is sent down the drill string. So, when its time, the moon pool gets opened up wide and we get to see the beautiful clear blue ocean under our boat, its quite a sight!
Here the free fall funnel is being put together around the drill string.
Then it gets lowered on a rope down to the water.
Then, they let it go! It free falls all the way down to the bottom of the sea and sticks in our hole! Watch it go in my video here: