Question

Drilling Course.

What are the disadvantages of adding solids to the water-based mud?

Answer 1

A mud is said to be contaminated when a foreign material enters the mud system and causes undesirable changes in mud properties, such as density, viscosity, and filtration. Generally, water-based mud systems are the most susceptible to contamination. Mud contamination can result from overtreatment of the mud system with additives or from material entering the mud during drilling.

Solids are materials that are added to make up a mud system (bentonite, barite) and materials that are drilled (active and inert). Excess solids of any type are the most undesirable contaminant to drilling fluids. They affect all mud properties. It has been shown that fine solids, micron and submicron sized, are the most detrimental to the overall drilling efficiency and must be removed if they are not a necessary part of the mud makeup. The removal of drilled solids is achieved through the use of mechanical separating equipment (shakers, desanders, desilters, and centrifuges). Shakers remove solids in the size of cuttings (approximately 140μ or larger). Desanders remove solids in the size of sand (down to 50μ). Desilters remove solids in the size of silt (down to 20μ). When solids become smaller than the cutoff point of desilters, centrifuges may have to be used. Chemical flocculants are sometimes used to flocculate fine solids into a bigger size so that they can be removed by solids-removal equipment. Total flocculants do not discriminate between various types of solids, while selective flocculants will flocculate drilled solids but not the added barite solids. As a last resort, dilution is sometimes used to lower solids concentration.