Other than the drill floor itself, the solids control system requires more attention than any other single rig system whether onshore or offshore. For that reason, it is most important that the solids control system is designed to be as efficient and as maintenance free as possible. This section will discuss that pan of the mud system extending from the bell nipple (or diverter housing outlet) to the mud pump suction piping.
Solids control is the most important function in mud treating. Control of mud properties centers around the treatment necessary to counteract the continual influx of drilled solids into the active mud system. Almost all of the costs of treating a mud can be directly attributed to solids control.
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]).