Dynamic kill, the ultimate goal of the relief well(s), requires the ability to shut-in against the remaining pressure (what the mud doesn’t provide). A broach would prevent that pressure from being applied for one thing.
This however, is one of several problems with the relief well operation. I doubt they have yet figured out how they are going to get that 16 ppg dual gradient kill mud to turn the corner in a 14.5ish ppg fracture gradient single gradient relief well.
Of course, they have the best minds in the world working on this project so the rest of us that have been doing this sort of thing for the last three decades can’t possibly tell them anything they don’t already know.
Could they try a top kill simultaneously with a bottom kill ?