1. n. [Drilling Fluids]
A 20- to 50-galUS [3.2- to 7.9 m3] container for liquid mud additives, usually located above the suction pit on a drilling rig. The chemical barrel is used to slowly dispense various types of liquids into the active mud system. It has traditionally been used to add caustic (NaOH or KOH) solution at a slow and steady rate to maintain a uniform pH throughout a circulating mud system. Adding caustic solution is an especially risky operation and the proper design and use of the chemical barrel for safety is vitally important. Derrick personnel must be informed of the dangers, proper protective clothing, and safety rules to follow when using the chemical barrel.