BAKER HUGHES - Drilling Fluids Reference Manual

MECHANICAL SOLIDS CONTROL
requirements by discarding solids in the highest concentration possible. The basic mechanical
solids removal equipment available falls into two categories – screening devices and enhanced
settling devices.
Dilution vs. Displacement 2
Dilution, as previously stated, is the most expensive and therefore the least desirable method for
controlling drill solids. In this case, a program of continuous dilution results in the dilution of the
already diluted fluid in each circulation cycle. Continuous fluid treatment to control chemical
concentrations, rheological and filtration properties, and density maintenance is required. A more
practical and economic method once considered is displacement. In this case, a measured volume
of the drilled solids contaminated drilling fluid is dumped and replaced with an equal volume of
drilled solids free fluid having the proper density, chemistry, rheological, and filtration
characteristics. In order for this procedure to be cost effective, the surface volume should be
maintained at minimum levels.
The concept of dilution vs. displacement economics has taken on other significance since the
disposal of fluids/solids/drilled cuttings came under more strict environmental regulation. Current
practices involve the minimization of all drilling fluids/solids waste. The application and effective
operation of mechanical solids removal equipment will minimize fluid dumping requirements.
Mechanical solids removal equipment should be sized and operated to remove maximum drilled
solids possible on a “first pass” basis. This will minimize the opportunity for drilled solids being
broken down into smaller sizes by repeated passage through the circulating system. This practice
will minimize dilution and dumping requirements.
The various types of solids removal equipment are described below.
Vibrating Screen Separators
Vibrating screens (shale shakers) are the first mechanical devices in the solids control system to
process the fluid. Maximizing the removal of solids at this point will increase the efficiency of the
remainder of the solids equipment utilized.
In unweighted fluid systems, maximum removal with shakers will reduce the solids loading on the
desander, thus lowering the chance of an overload condition, which in turn, will lower the chance
of overloading the downstream desilter. The cascading effect of a solids control system points out
the importance of having each piece of equipment operate to its maximum potential, thus allowing
the downstream units to do the same. Since the operation of the shaker affects the remainder of the
equipment, it must be sized and utilized correctly for the system to remove the maximum amount
of solids.
Fine screen shakers should be used on any operation where optimum solids control is desired, but
they are particularly suited for operations employing weighted fluids, high-cost fluid-phase fluids,
and oil-base fluids. When weight material is carried in the fluid system, the options for removing
solids without removing the weight material are limited to screening and centrifuging. If weighted
2 Beasley, R.D. and Dear, S.F. III, A Process Engineering Approach to Drilling Fluids Management, SPE
19532, Presented at the 64 th Annual Technical Conference, San Antonio, TX, October 8-11, 1989
BAKER HUGHES DRILLING FLUIDS
REVISION 2006 10-7
REFERENCE MANUAL