c.captain,
My background is drilling so maybe I can help, but I want to emphasize no one will [U]know[/U] what happened for quite some time, and that the prospects for the eventual understanding are excellent. I don’t want to fuel speculation but maybe I can lend some insight to what [I]may[/I] have happened…
The casing would have been engineered such that it would have been extremely unlikely, if not impossible, to collapse. Even under such extreme conditions. Even if what you say did happen, it’s unlikely any well flow came up outside of the BOP. It is most likely (subsea hands weigh in) that the Deadman feature closed when the conduit line pressure was lost - as the rig capsized and the riser finally crumpled.
I am assuming the kick got into the riser above the BOP’s somehow. Once this happened meaningful pressure control would have been lost and it would have been virtually impossible to control the fluid’s expansion and release of entrained gas at surface, on the rig.
If anyone here has had scuba training, you know the effects of hydrostatic pressure on gases. The volume of gas is controlled by Boyle’s Law. In effect, as the kick approaches the surface the hydrostatic pressure decreases, the gas bubble expands. The rate of expansion is exponential, hence what you say is correct - the last 100’s of feet would have been the quickest and most severe and there may well have been no time to react - and no meaningful way of controlling it anyway since it had long been in the riser.
Regarding other posted comments that the ocean’s hydrostatic pressure would have killed the well: Probably not, for quite a few reasons.
The black smoke says Oil, but there is no reason to think there would not be plenty of associated gas breaking out at surface conditions too. A gas-only kick would be a bright orange flame and very little smoke. As an Armchair Quarterback: The intensity I saw was in keeping for an oil well blowout (yes, I have seen one personally).