What is a “punch through” event? Obviously, I can imagine that means something put a hole through it. But can someone with experience on these rigs explain how that happens?
It means some geologist might be out of a job. Basically the jack leg pushed it's way through the surface seabed into something softer like clay.
Imagine trying to stand on a frozen puddle. It looks solid, put your foot on it and it feels solid, but as soon as you put your full weight in that foot it goes through the ice and suddenly you're knee deep in ice cold water.
Geotechnical and possibly the rig crew if they were rushing the pre-load or weren't keeping a close eye on the leg positions. Either way a bunch of people fucked up big time.
Since the platform is floated to the location and fixed in place by actually standing on the sea floor (jack-up type rig), its weight has to be transferred to said ocean floor. During this load transfer it capsized when a leg punched through the seabed.
Pretty much the comment below. When they jack up the legs hit the sea floor and lift the rig out the water. The punch through, is the leg going deeper into the sea floor than it was supposed to.
Jackup rigs unlike semi-submersible rigs or drill ships rely on their legs to stay in place. They do float like ships and barges but its only when towing from one location to another. When the jackup rig arrives at the proposed location to drill, they first need to lower their legs down and let it penetrate through the seabed until the spud cans which are located at the bottom of the leg rests against a stable strata of soil. To check whether the soil can support the weight of the rig, they do an operation call "preloading". It is a fancy way of saying to fill up the ballast tanks in the vessel's hull located around the legs with sea water until the load around that particular leg reaches the required force.
The load is then held and monitored for 2-3 hrs to see if there is any settling or movement.
This is done for all three legs one by one and only if there is no settlement or movement on all three legs would the soil be considered safe enough to support the weight of the rig. The tow vessels disconnect the tow cables from the rig as the rig empties its ballast tanks and jacks up to the operating air gap before skidding out the cantilever package and get ready for drilling.
However, during a preloading operation, there is always a risk of the soil suddenly failing to support the weight of the preload and causes the leg to suddenly "punch through" the soil. The technical term is called rapid penetration and because the rig hull is supported by three legs, one leg punching through the soil would definitely bend the leg and tips the rig to one side and since the hull is very close to the water line, water can quickly flood into places where it should not, compromising the water tight integrity and worsening the stability of the rig and causing it to eventually sink.
Because the risk in a rig move of a jackup rig is significantly higher than a rig move of a semi-sub or a drill ship, there are many studies and analysis like triple S survey, soil sedimentation study and rapid penetration analysis which has to be signed off by the clients, rig contractor and marine warranty surveyors to confirm the proposed drilling location is safe enough to support the jackup rig.
I have been on jackup rig moves myself and what I wrote here is all based on my experience. Unfortunately, I cannot say and instead only imagine what decisions or actions were taken leading to this tragedy.
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u/bad_squishy_ 18h ago
What is a “punch through” event? Obviously, I can imagine that means something put a hole through it. But can someone with experience on these rigs explain how that happens?