The presence of large amounts of drilled solids in a drilling mud usually
spells trouble for the drilling operation. These solids adversely affect the performance characteristics of the mud and can lead to a multitude of costly hole problems.
Drilled solids decrease the life of a mud pump’s parts and thus, can decrease drilling efficiency due to lost time for pump repairs. Continued recirculation of drilled solids produces serious mud problems because recirculated solids
will gradually be reduced in size. The smaller the solids become, the more they negatively influence mud properties and hydraulic performance. The greatest impact of the solids is seen in reduced ROP. The higher the drilled solids content, the lower the penetration rate.
If mud solids are not properly controlled, the mud’s density can increase above its desired weight and the mud can get so thick that it becomes extremely difficult or even impossible to pump.
Since the earliest days of the oilfield, drillers have been trying to combat high solids content through the use of settling pits. However, some drilled solids are so finely ground that they tend to remain in suspension. This results in increased mud viscosity and gel strength which, in turn results in
larger particles also remaining in suspension. Thus, the approach of removing cuttings through settling alone is of limited practical value.
Solids control equipment was developed in order to more effectively remove unwanted solids from drilling mud. A variety of devices are available which mechanically separate the solids particles from the liquid phase of the mud. Thus the driller, depending on the particular situation and equipment used, can regulate to a fine degree the amount and size of solids particles that are removed or maintained in any given drilling mud.
Such control of mud solids through mechanical separation allows the mud to perform its drilling-related functions and avoids the downhole problems caused by excessive solids contamination. Effective solids control permits viscosity and density to be kept within desired levels, dramatically increases the life of pump parts and drill bits, and promotes faster penetration — all of which decrease the time and expense of drilling.