At the Deepwater Horizon ground zero location, today, BP will test the cap it has put in place as well as the integrity of the entire well system.
Figure 1 shows the concept of the entire well assembly with the cap placed over the BOP (blow-out preventer), shows the pipe going up to the rigs floating on the surface of the gulf, and shows the well casing going down to the oil reservoir deep under the seabed.
Figure 2 shows what the well assemblage will look like if the cap works and if the well casing under the seabed down to the oil reservoir is intact, that is, not damaged.
This is the best possible scenario, especially at this time of hurricane season.
The cap would allow the site to be completely abandoned during a hurricane without any more oil / gas leaking into the gulf waters.
Figure 3 shows the worst case scenario, meaning a disaster far worse than what we have now, even though that does not seem possible.
There are two problems shown in the Figure 3 graphic: 1) a deep breach in the well casing allowing oil / gas to leak into the strata layers around the well bore (raw hole) and well casing (metal pipe), and 2) a shallow breach near the sea floor that ruptures the seabed making a crater, then allowing a full on gusher of the oil / gas into the gulf waters.
If the Figure 3 shallow breach scenario happens there is no stopping the catastrophe unless the relief well being drilled works to shut off the oil down closer to the oil reservoir.
Lets hope the cap works and the well casing also holds.
They will know if there is a well casing breach because the pressure at the cap will be low, or will continue to decline as oil / gas leaks out through the well casing into the layers of rock and other strata around the well casing.
If the pressure at the cap holds at a high level, that will indicate that the well casing is intact and has not been breached.
The concern about a breach arose when they tried the "top kill" by pumping "mud" into the well casing to plug the well.
The mud went somewhere, and one of those places it went could be out a breach in the well casing into the strata around the well bore and well casing.
They are wise to slowly close the valves in the cap and closely monitor the pressure level as they do, otherwise the whole assemblage could blow again if the pressures go wild.
Again, may the cap hold!
UPDATE: Washington's Blog shows, in forbidden photos, what has happened, and unfortunately what will continue to happen for months or years, even if the cap works.