It is not a procedure where control has been lost over the well, like a blowout.
The process involves pumping heavyweight drilling mud into the well.
This procedure is expected to stop the flow of oil and gas from the well.
[1] The top kill procedure was used to plug flaming oil wells, blown up by retreating Iraqi forces, in 1991, during the Gulf War.
[2] This technique came to prominence during the 2010 Deepwater Horizon oil spill when it was used in an attempt to seal a seafloor oil well after the failure of the blowout preventer.