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.
A field application of the economic and performance analysis model for a closed-loop system implementation. A district had realized substantial benefits through more effective solids control in earlier years and was interested in 1986 in analyzing the economics of further improvements in solids control. The economic and performance analysis programs were run to predict the costs, potential savings, and recommend a suitable solids control system. It was a nine-well (2-vertical and 7-directional, 4300 ft average depth) infill drilling program within the city limits, which imposed certain constraints such as minimal or no reserve pits with all the extra mud and wastes hauled for off-location disposal.
In the drilling process, mud materials (barite, water, treating chemicals, etc) are mixed almost continuously to maintain desired mud properties. Drilling mud usage is defined as the volume of mud that is lost with the
drilling operation. This should be contrasted with mud consumption which is the total volume of mud created to support the drilling operation.