It's become obvious from BP's doublespeak and moving of the goalposts that the "top kill" hasn't worked. I'm beginning to believe exactly that; that BP knows the top kill has failed, but that they are continuing to pump mud out on the ocean floor rather than admit it. Typically, you know pretty quickly if a top kill works. BP has been pumping the kill since Wednesday, trying a number of tactics, including junk shots. Their announcement last night that it would be at least through the weekend before they know the results of the kill doesn't ring true to me. Certainly they know a lot more than what they are saying.
Recall that a top kill will work only if enough back pressure can be generated in the leaking wellhead to allow the pumped mud to overcome the pressure from the well, turn the flow around, and then build enough hydrostatic head to overcome the formation pressure. The junk shot was designed to do just that, but apparently BP had decided to try just mud for the first effort. I believe that the high rate that BP pumped the mud washed out the cracks in the riser, actually reducing back pressure. The cracks in the riser are where you saw the mud flowing if you watched the live feed of the top kill the last couple of days. As a side note, I do find it interesting that the BP feed no longer includes the bent riser view of the last couple of days,and now looks like the end of the riser where the riser insertion tool had been used previously.
The because of the washed out riser cracks, the bridging material pumped in for the junk shot probably can't clog up the riser and BOP enough to overcome the flowing pressure and allow mud to go down the well, so the mud they are pumping is likely just going into the kill and chokes valves and coming out the top of the BOP. That's not all bad, of course, if the pressure of the mud is at least restricting the flow of oil from the well, but it is certainly not a long term solution, and they are risking washing out the riser even further.
I'm now hearing that BP determined the top kill failure sometime in the last 24 hours, but rather than announce it, have decided to just keep pumping until the next alternative is decided, either the LMRP (lower marine riser cap) cap to bring flow to the surface, or removing the LMRP and landing a new BOP on top of the failed one.
I'll continue to monitor this recent development, but I'm not expecting good news in the near term.