BP has been moving the target date for the top kill on almost a daily basis, using vague explanations about staging, equipment, etc. I have suspected that there was something else going on, and, based on past experiences with BP, you can almost be assured that there is.
On the Today Show this morning, BP CEO Tony Hayward talked with Matt Lauer about the top kill. Matt was pressing him about timing of the procedure, and Hayward was characteristically vague. He claimed that the BOP was "rebuilt" this week, although we know work on the BOP has been going on since day one, and we all know that the top kill was the only real solution to this blowout short of a relief well. I don't believe that the rebuilding was done just this week, and believe that the kill manifold, built during the first 2 weeks of the blowout, was set on the sea floor 2 weeks ago. Hayward said that were monitoring pressures and "flow paths" which tells me that they do know how much the well is flowing, but won't say. Have a look at the clip:
I now believe that, indeed, BP has probably been slow playing the top kill to allow the well to blow down to a lower pressure, assuring a better chance of success. Remember that the top kill is a difficult procedure that requires the weight of the mud, along with the rate that it's pumped, to essentially overpower the flowing well to stop it, and then turn it around by pumping mud down the hole. Anyone who has had a basic science course knows that fluids always follow the path of least resistance. In this case, the path of least resistance is up, out the riser. In order for this to work, enough friction, creating back pressure, will have to be generated in the BOP and the wrecked riser allowing the pumped mud to overcome the force of the flowing oil and gas. Once that happens, hydrostatic head of the mud will take over, pushing the oil and gas back into the reservoir. Here's a pretty good illustration:
As we've talked about before, the bottom hole pressure was originally about 19,000 PSI based on reports that the kill weight of the mud was about 16 lbs per gallon. Assuming that bottom hole pressure is now about 12,000 psi, it would require that amount of hydrostatic head to get the well to stop flowing. They already have about 2,200 PSI on the top of the well by virture of the pressure of 5,000 feet of water column, so they would need another 9,800 PSI of hydrostatic to kill the well. This would require them pumping 16 lb mud down to about 12,000 feet below the mudline, using simple calculations. They would probably start with a heavier mud with high viscosity (thickness) to create more friction in the BOP and to help get the well turned around. These numbers are simply for illustration and there are a lot more variables, obviously, that could effect the specific proceedure they will follow, but this gives you an idea of what BP is up against.
If BP announced they were waiting for the well to blow down before attempting the top kill, a public furor would ensue. Since they have virtually no credibility left with the public, I believe that they probably decided to just take a long time to get the mechanicals in place while waiting for the well pressure to decrease. If they delay the kill again today, it will be likely because they believe the wellhead pressure is still too high.
One other note. The video feed that are showing is actually the wrong one. I would much rather be looking at the leak in the riser on top of the LMRP, above the BOP. That would give a much better indication about what is going on in the well during the kill. You can bet that's the one BP is watching.