The decanting centrifuge is used in weighted mud applications to recover valuable weighting material from mud which must be discharged due to unacceptable colloidal solids content. The decanter centrifuge settles out barite and coarse drilled solids which are returned to the active mud system to maintain density. The relatively clean centrate containing liquid and colloidal solids is discarded. These colloidal solids cause many drilling fluid problems, such as high surge/swab pressures and ECDs, differential sticking, and high chemical costs. Usually, the value of the weighting agent in these mud systems makes it economic to recover the weighting agent from the whole mud before it is discarded. Fig. 1 gives an example of the economics of centrifuging weighted muds.
Stoke’s Law, which gives the mathematical relationship of the factors governing the settling velocity of spheres in a liquid stated in its simplest form as:
JB = dD² (Db – Dl) G / 18μ