Decanting Centrifuge In Weighted Muds

Overlook decanter centrifuge

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.

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THE DIFFERANCE BETWEEN WEIGHTED AND UNWEIGHTED MUDS

Water as a drilling fluid does not qualify as a mud. If there are no hole (formation) problems that prevent its being the most economical drilling fluid; if neither the geologist, palentologist, nor production supervisor have valid objections; and if it is available, water is seldom if ever surpassed. When the formation requires, or a supervisor demands , filtrate control and / or viscosity and /or gels in the drilling fluid, a “mud” is built. Or if the fluid density required is too high for salt water alone , mud properties are required to suspend barites.

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DECANTING CENTRIFUGES

The decanting centrifuge is the only liquid-solids separation device used on drilling fluids that can remove (decant) all free liquid from the separated solids particles, leaving only adsorbed liquid or “bound liquid ,” on the surface area. This adsorbed liquid is not prone to contain solubles, such as chlorides, nor colloidal suspended solids, such as bentonite . The dissolved and suspended solids are associated with the continuous free liquid phase from which the decanting centrifuge separates the inert solids, and are removed with that liquid. The adsorbed liquid can only be removed from the separated solids by evaporation, which has been neither desirable nor practical so far in drilling mud work.

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