Weighted muds are the ones that contain weighting materials. These mud systems are usually used for drilling at deeper depths because of increasing formation pressures. The typical composition of weighted clay/water mud is active clay, and inert solids like barite are used for enhancing the mud weight. As mentioned earlier, the mud arriving at the surface from the bottom while drilling is in progress contains active and inactive drilled solids. Hence, the low gravity solids must be removed first, using a screen, because their disintegration reduces the particle size to less than that of barite or in the similar range. This may cause a loss of costly barite if the mud is subjected to solids control. Once the larger particles are removed the mud must be passed through mud cleaner, where the hydrocyclones are used in series with screens. This system works best for muds with density less than 15.0 lbm/gal.
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.
Proper application and utilization of mechanical solids control equipment enables the driller to maintain the desired drilling fluid properties which in turn makes it possible for the drilling operation to be carried out in an efficient and possible for the drilling operation to be carried out in an efficient and economical manner.
The combination of fast drilling, gumbo clay, and conventional solids control equipment operations can create a variety of issues:
- High losses of drilling fluid through the solids control units.
- High volume of dilution.
- High volumes of fluid processed requiring strictly regulated disposal to protect the environment.
- Continuous plugging of the mesh in the solids control units.
- Increase in the consumption of screens.
- Fluid overflow due to plugging of the screw conveyors.
- Poor supervision of the solids control units.
- Increased operating costs.