A slurry that is composed of barite, a phosphate thinner, and water. A barite plug is used to control an underground blowout in which a well is kicking and losing circulation at the same time.
If you have mixed out the mud weight and still have trouble controlling pressure, one way to heal the high pressure zone is to send a plug of barite or cement downhole, pull two or three stands, reconnect the kelly, and circulate for 24 hours.