1. The density of known mud volume in units of lb/gal.
2. The prevention of flow of formation fluid into the wellbore or the hole.
3. To ensure that the drilling fluid must exert a greater pressure than the formation fluids penetrated by the bit
4. That the pressure exerted by the mud at any depth was related directly to its density.
5. The loss of circulation that may result from excessive hydrostatic pressure due to