**1. n. []**

Mathematical relationship between the densities and the corresponding volumes of mixtures of liquid-solid slurries and clear fluid blends, such as drilling muds and completion fluids. Assumptions are: (1) masses and volumes of components are additive and (2) material is neither generated nor lost from the system. As a simple example, below are the two material-balance equations for a three-component mixture of oil (o), water (w) and solids (s), where V = volume percent, D = specific density and MW = mixture weight. (This could represent a simple, weighted oil-base mud formulation.)

MW = DsVs + DoVo + DwVw

100% = Vs + Vo + Vw.

**See related terms:**
high-gravity solids,
low-gravity solids,
make-up water,
mass balance,
mud density,
retort solids,
slurry