In the oil well drilling industry, mud density is a measure of the weight of the drilling fluids in a given volume and is normally measured in pounds per gallon (lbm/gal) or (ppg). It is frequently referred to as mud weight. In the operation field it is measured using a mud scale or mud balance. The instrument consists of a constant volume cup with a lever arm and rider calibrated to read directly the density of the fluid in lbs/gal (water = 8.33 lbs/gal) and pressure gradient in psi/1000 ft (water = 433 psi/1000 ft) or pounds per cubic foot (water =62.4 lbs/ft).

(Mud Balance)

The mud weight is related to the specific gravity of the drilling fluids. Specific gravity is the ratio of a materials density to the density of water. Pure water has a specific gravity of material twice as dense as water would have a specific gravity of material half as dense as water would have a specific gravity of 0.5. Low gravity solids have an average specific gravity of 2.6. The solids are 2.6 times the weight of the same volume of water.

(Decanter Centrifuge)

In traditional drilling fluids, barite is used to increase the mud density in order to condition the proper drilling fluid that is required by the drilling formation. Other chemical additives such as halite (salt) or calcium carbonate can also be used for increase the mud weight. Mud weight can be decreased by dilution or solids control equipment such as a decanter centrifuge. A proper designed decanter centrifuge can recover barite as much from the return drilling mud.