I don't understand the 'junk shot' plan. They're talking about shooting old golf balls, knotted rope scraps, and shredded tire chunks in, followed by cement? I guess I just assumed that in such a highly engineered industry, they'd have a design and spec for the 'junk', rather than relying on what sounds like random, uncontrolled, scrap.
Maybe that's just popular description, and in reality the junk in the junk shot is very well controlled?
I think it really is junk. The NYT(? I think) had an interview with someone who used junk shots to close wells in Kuwait, and his favorite junk was lamp cables because it contained both soft plastic and harder copper wires. My understanding is that they are looking for something that they can pump into the BOP, and that once inside will form a nice big tangle and hopefully plug up the leak. What to use depends on the specifics of each leak and is more an art than a science.
I also read up on the BOPs a bit--very interesting. I would have expected a last ditch line of defense consisting of some sort of powerful spring-loaded ram with a maybe an explosive and/or mechanical trigger, so that if everything goes wrong, you can hook up a sub and yank something to clamp the stem, even with no hydraulic lines connected.
Not that the annular BOP isn't a clever design, using the well pressure against itself to clamp down tight.
Maybe that's just popular description, and in reality the junk in the junk shot is very well controlled?