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.
The application of polymer muds has been hindered by two criticisms. First, they are difficult to run because mud-engineering maintenance guidelines are very different from conventional bentonite mud systems. Second, they are less solids-tolerant than dispersed or lime-based systems. Consequently, these muds often have proved uneconomical for drilling geologically young and highly dispersive shales or for drilling with high mud weights (greater than 14 lbm/gal [greater than 1700 kg/m3]).
The volume and type of solids in a drilling mud system can adversely affect mud properties, reduce penetration rates, cause damage to drilling equipment, and increase total drilling costs. Efficiency controlling the solids content of the mud system is an important phase of an efficient and cost-effective drilling program. The three basic methods of removing solids are dilution and/or displacement of whole mud, settling and mechanical solids-control equipment.
An important problem in the oil industry is the treatment of produced water, especially in the case of offshore oil production where space and floor area, needed for the separation equipment, are extremely costly. Increased production of water occurs when an oil field matures, and the availability of efficient and cost-effective techniques partly determines the period during which economic production is possible. For the final de-oiling process several techniques are available, of which plate separation, centrifugation and the use of hydrocyclones are important ones. Common characteristics of these three techniques are that only insoluble oil components can be removed, and that the prevailing separation process is movement of the oil droplets with respect to the continuous phase, water, as a result of an external force, viz. the gravity force or the centrifugal force.