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.
Fine solids resulted from formation cuttings were contaminants that mostly caused unstable mud performance. Combination of batch drilling sequence and unsuitable solids removal treatment, led to fine particle accumulation. This is one of the root causes of excessive torque and high ECD throughout the drilling operation.
From drilling fluid properties point of view, it is beneficial to minimize drilled solids content. This can be achieved by mechanical treatment, chemical treatment, dilution, and/or mixing new mud. All the above methods, will lead to additional cost impact. Thus, utilization of proper solids removal was required to balance between mechanical treatment and dilution method to reduce solids at acceptable cost.
Drilling fluid cleaners were equipment of solids control, also called mud cleaner or mud conditioner, etc.. Drilling fluid cleaner was evolved in the early 1970s to remove fine drilled solids from medium weighted mud without excessive loss of barite and fluid. It is also proved valuable tools in drilling loop closed systems and other applications (dispersed weighted). Drilling fluid cleaner use a combination of desander and/or desilter hydrocyclones and very fine mesh vibrating screens (120~400 mesh) to remove fine drilled solids while returning valuable mud additives and liquids back to the active mud system.
The overall efficiency of cuttings removal by the solids-control system, Es, can be expressed as:
Es = E1 f 1 +( 1 – E1 )E2 f 2 + ( 1 – E2 )E3 f 3 +( 1 – E3 )E4 f 4 (1)