Im not a petroleum engineer but this is my understanding of how it works:
You add a fluid/mud down the well. The desity of the fluid has been adjusted in advance so that the weight of the liquid collumn outbalance the pressure down hole.
I dont know if plugging the well with concrete or whatever is a part of it too.
If you work on a platform why dont you just ask around?
Thanks for the info. Actually I am not working on the platform. We are engaged in a platform design project at this moment of time. So this is my very first time to encounter such term.
but seriously - if you need to know details of this there must be somebody you can ask?
Anyway my description is correct in general terms. Im not very much aware of how its done with regards to operation details such as how to adjust the desity of the mud - but i think adding barium in varying amounths is used.
MortenA is generally correct. Barite is used to increase solution densities as required. In addition the solvent used may not be water only. I believe you reach a limit of about 16-17 pounds per gallon with water based muds. I have seen oil based muds that run upwards of 20 pounds per gallon. The heavy solutions can be used to "kill" a well if during operations the platform were to "take a kick". Ultimately the goal is to maintain control of the well. If hydrocarbons were allowed to vent at the surface (otherwise know as a blow out) there is a hugh chance of fire/explosion. If you were working on that platform, that would a very bad thing. As for plugging the well with cement that would not be of benefit. Cement solutions run 15-16 pounds per gallon and require typically 8 hours to cure and provide any appreciable strength. More over during this time natural gas can and will channel it's way to the surface. Also, it cost someone in excess of millions to drill that hole. Why would the plug it if they didn't have to?