1. n. 
A slurry that consists of bentonite, cement or polymers mixed into an oil; bentonite in diesel oil is commonly used as a gunk plug. A small batch of the slurry is pumped down a well that has lost circulation to seal the leaky zone. The gunk plug may or may not be squeezed by pressure into the zone. Water downhole interacts with the bentonite, cement or polymers to make a sticky gunk.
Synonyms: diesel-oil plug