[Yo-Yo]

Instead of sticking a tube inside the riser, why not put a larger diameter tube outside of the riser. That should capture all leakage from the broken riser.

Then you still have the leaking blowout preventer to deal with.

[Donald Rumsfeld Fan]

has to accomodate pressures. think of how you would use a straw when sucking on some fluid from a container.

[prisoner6]

That still makes the most sense to me. However it is in deep water with LOTS of pressure/ But why nhot a larger tuboe overtop, then slowly reduce the size of the outer tube?

Maybe the hydrate problem again.