From what I understand, they need to push the oil far down the hole. They are pumping some outrageous volume of mud down the hole to push the oil deeper down the well. Like 55 gallons every few seconds. I think that is causing the increased flow from the broken riser seen on the video. Eventually they flow of mud will be changed to to fast setting cement. Pray that the cement can withstand the pressure and set. If so, well is plugged.
The cement doesnt have to withstand pressure per say. They fill the hole with “mud” and it’s weight exceeds the upward pressure so nothing comes up. Then they follow up with cement which weighs similar to the “mud”, which isn’t mud at all. It’s over twice the density of water, barium something or other. Note, that if the upper part of the casing to rock seal is compromised, of if the the upper part of the casing fails in some way, then intercepting and killing might be the only solution. But the flow hasn’t been to high so erosion hopefully won’t be to big a deal.