[east1234]

My understanding is that a lot of drilling “muds” are Bentonite, basically a clay to seal cracks and lubricate the bits and ease extraction of the cuttings. BP is using “heavy” drilling mud. It is designed to deal with higher pressure situations, it is much heavier (specific gravity). Google both if you care to.

[Sudetenland]

FYI YOu are largely correct. The basic mud is bentonite clay and water. The weighting agent is barium sulfate, or barite, specific gravity 2.9 (water is 1.0 or 8.33lbs./gal.). They will also put various chemicals in it like dispersants such as lignite, lignin, sodium acid pyro-phosphate, etc. to keep the mud from becoming too thick.

You have now had a brief introduction to mud.:)