I’m not exactly clear on the orginal cement operation. But it was at depth. It would have been to seal the oil producing zone off from the annulus (outside) of the hole above the oil zone. The well is double-cased, so this would include between the outer casing and the rock, and between the inner pipe and the outer casing.
I believe that the idea was once this deep cement job had “set up”, then they would remove the heavy mud from the well and replace it with seawater. And once that was done, put a shallower cement plug into the inner well pipe.
But yes, if there is a breach at depth of the well, which there obviously is, the oil under pressure may be working its way up along the outside of the outer casing - between the rock and the casing.
When it reaches the soft mud at the bottom of the gulf, I would imagine that it will both disperse into the mud, and start creating a subsidence near the well., which could cause further harm to the shallow portion of the well I suppose.
Thanks. Not good no matter what.