Originally I believed that the casing was cemented solid and had not  failed. When that is the case, bolting a gate valve or BOP onto the  stack is an appropriate method of solving the problem. Since then I have  learned that the downhole casing is NOT intact. The 9-5/8" segment of  the casing (casing is set like an inverted layer cake with the largest  casing near the top and successively smaller casing set lower in the  well to minimize the hung weight of the casing string while optimizing  for tensile strength.) has been blown out of the well and the casing  hanger (which has hardened gripper blocks to grip the side of the larger  casing) is currently lodged in the BOP, which is one reason why the BOP  shear rams were unable to close in the well, too much hardened steel in  the way. This means that the lower section of the wellbore is no longer  cased. It is "open hole" and that means that the oil and gas can  migrate into the formation and concievably flow up around and past the  wellbore casing. In this well control configuration, you need to keep  the well flowing with as little back-pressure as possible to prevent the  fluids from trying to seep out of the wellbore while you prepare a  relief well to to a "bottom kill". Imagine you have a garden hose that  the dog has been chewing on and it has a bunch of bite holes in it. As  long as you don't screw the sprayer nozzle on the end, the water doesn't  spray out the holes because there is an easier leak path, but once you  screw the nozzle on and restrict the flow, it starts spraying out the  holes. Same thing in this situation, the fluid wants to follow the path  of least resistance and we need to keep that path inside the wellbore  where we can control where it goes not bubbling up all over the seafloor  where we can't collect any of it, so it is probably for the best that  the BOP did not close because then it would have simply percolated up  around the well and it would have been virtually uncontrollable then  because once it starts flowing around the wellbore there is no way to  stop it and it will only flow more and more as the flow path is eroded  and opened up.         
Many people have lamented and protested that BP should have closed int he well months ago and have come up with myriad off the wall ideas to close in the well. The problem is  that there is no such thing as a one size fits all well control  methodology, and even if there was, it would unlikely be something you  could wave a magic wand and have it instantly be implemented, most of  them take some amount of time to prepare and implement, some more, some  less. Yes, the well is making one heluva ecological mess and hundreds of  millions of dollars are being lost every day so it behooves everyone to  work as fast as possible but in this situation you can't let that be  the only consideration because if you do, you will invariably chose the  wrong control strategy and make things worse instead of better. Cutting  corners and taking risks is what got us into this mess, it is unlikely  to get us out of it. There are times when you must allow things to  proceed while you bide your time and prepare, this is one such time.
         That said, the first relief well is almost in position. It has made  one "ranging run" where the drill is run offset and past the wellbore to  allow the magnetometers in the directional guidance package behind the  bit to more accurately locate the wellbore. They will back off and drill  two or three more bypasses to get an accurate picture of the location  of the wellbore before they attempt to drill into the wellbore. Then  they will set casing and pump cement to seal off the annular area around  the relief well's casing before they make a final assault on the blown  out wellbore. This is the most ticklish part of the relief well process  and they must work slowly and carefully. I expect they will be preparing  to make the final assault on the wellbore over the july 4th weekend, if  not a bit sooner. They are well ahead of schedule, but again, you don't  want to get too ahead of yourself or you'll make mistakes, we've had  enough of those.