The use of “dewatering units,” as a regular part of the drilling fluid treatment process on drilling rigs, continues to increase. A dewatering unit, the final phase of a solids control program, is designed to discard no free liquid. A solids control program in which a dewatering unit is used is referred to as a “closed-loop system” (CLS), “sump-less system,” or “chemically enhanced centrifugation” (CEC).
Offshore drilling rigs operate in very sensitive environments surrounded by water. Waves can wash seawater onto the rig. Monsoons can completely cover the deck with a thick layer of water within a couple of minutes. Oil spillages can end up on the drill floor because of a mistake or a mechanical failure.
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.