The flexible pipe has to be strong enough to withstand 160 bar, wide enough to allow the necessary flow, and at the top tolerate one mile of pipe - filled with water - pulling on it. I have no intuition how challenging that would be. Or maybe it does not have to be very flexible, after all submarine gas pipeline are also flexible to some extend. This seems the more realistic option to me if material science does not get in the way.

On the other hand disassembling two miles of a segmented pipe like the ones used for oil drilling in an hour or two does sound pretty ambitious. Drilling pipes are - according to a quick search - up to 45 ft long, so one would have to unscrew more than 200 connections. One could use longer sections but that will probably complicate the handling at the surface and might not actually help in terms of time.