The endgame is tricky. No one knows the condition of the well bore deep below the gulf. It's conceivable that the bottom of the well has eroded around the steel casing, said Charles West, a geophysicist who has consulted for the petroleum industry and worked on relief wells. If that's the situation, he said, drilling into the casing would be "like trying to chase a strand of spaghetti around with a spoon."
That would force the drillers to back up and aim a bit higher on the well. Finding the target is critical. The drill bit can't turn on a dime; if it misses, it will have to be backed up for another approach.