Lime muds

A hydrolyzed cereal soHd, predominately a hexasaccharide, is used in high pH lime muds for reducing the yield point and gel strength (67). This additive has been used in systems treated with both sodium hydroxide and potassium hydroxide in addition to other additives common to lime muds (68). A second viscosity-reducing additive used in lime muds is a graft copolymer of acryflc acid and calcium flgnosulfonate (69). Both of these materials are used at levels of 6—17 kg/m (2—6 lb /bbl). 

The second most common alkalinity control agent is lime [1305-78-8] normally in the form of calcium hydroxide [1303-62-0], used in both water and oH muds. In the latter, the lime reacts with added emulsifiers and fatty acids to stabHi2e water-in-oH emulsions. Lime is used in brine systems containing substantial quantities of soluble calcium and in high pH lime muds. Concentrations are ca 6—57 kg/m (2—20 lb /bbl) (see Lime AND LIMESTONE). 

Potassium hydroxide [1310-58-3] is occasionaHy used for alkalinity control. This is particularly tme for some polymer and lime muds where a low sodium level is desired. The potassium level of such muds is quite low but has been attributed by some to provide stabHity to water-sensitive shale formations (68,93). 

The white Hquor is separated from the calcium carbonate by decantation in a clarifier and is then available for a new cooking cycle. The underflow from the clarifier, which contains the calcium carbonate and is referred to as lime mud, is diluted with water and passed to a second clarifier known as the lime mud washer. The clarified weak white Hquor (weak wash) goes to storage and then enters the dissolving tank. The lime mud residue from the lime mud washer is passed to a rotary filter and subsequently to the lime kiln where calcium carbonate is converted back to calcium oxide, thus completing the lime cycle. 

Caustic soda is removed from the carbonate—bicarbonate solution by treating with a slight excess of hard-burned quicklime (or slaked lime) at 85—90°C in a stirred reactor. The regenerated caustic soda is separated from the calcium carbonate precipitate (lime mud) by centrifuging or rotary vacuum filtration. The lime mud retains 30—35% Hquid and, to avoid loss of caustic soda, must be weU-washed on the filter or centrifuge. Finally, the recovered caustic solution is adjusted to the 10% level for recycle by the addition of 40% makeup caustic soda. 

Inhibited Muds—Dispersed Systems. These are water-base drilling muds that repress the hydration and dispersion of clays. There are essentially four types of inhibited muds lime muds (high pH), gypsum muds (low pH), seawater muds (unsaturated saltwater muds, low pH), and saturated saltwater muds (low pH). 

Lime-treated muds are prepared from freshwater drilling muds. The conversion should be made inside the basing. The initial step in conversion of freshwater mud to a lime mud involves dilution of the mud with water to reduce the clay solids content to avoid excessive mud viscosity (breakover). The recommended sequence of material addition is... 

The limitation of lime-treated mud is solidification at bottomhole temperatures higher than 250°F. Low lime mud was designed to minimize this tendency toward solidification and can be used at bottomhole temperatures as high as 350°F. In low lime mud, the total concentration of caustic soda and of lime is reduced. The recommended P is from 1 to 3, and the recommended P is from 10 to 15 the excess lime should be from 2 to 4 Ib/bbl. 

Water-based drilling muds that repress hydration of clays (lime muds, gypsum muds, seawater muds, saturated saltwater muds)... 

Calcining. In the calcining process, the lime mud removed from the white liquor is burned to regenerate lime for use in the lime mixing step. The vast majority of mills use lime kilns for this process, although a few mills now use newer fluidized bed systems in which the reactants are suspended by upward-blowing air. 

Calcining (lime kiln) Lime mud Lime Fine and coarse particulates Air... 

Both classifications are based on the depositional texture of the limestone Folk s emphasis is on the similarity of carbonate sedimentation to that of sandstones, resulting in a scheme employing as variables the lime mud spar cement ratio and allochem composition. Allochems may be intraclasts, ooids, fossils or... 

Neumann A.C. and Land L.A. (1975) Lime mud deposition and calcareous algae in the Bight of Abaco, Bahamas A budget. J.. Sediment. Petrol. 45, 763-786. 

---