This very large blowout occurred in Bangladesh and was originally estimated at over 100 mm/scf/D.
When it blew in the operator only had limited surface casing in the hole and the flow quickly breached to the outside of the pipe causing a cratering or caving situation under the rig.
One rig was swallowed up and disappeared completely.
Once flow becomes established “outside” of the pipe a surface intervention is no longer possible and the only option is to directionally drill into the original well bore, intersecting it as low as possible and then killing the well through that channel.
This photo is of a second rig when the same type of event, cratering, is again beginning and this rig would eventually be lost as well. Note that much of the rig support equipment is sinking.