1.
n. [Drilling Fluids]
A type of
water-base mud that is saturated with lime, Ca(OH)
2, and has excess, undissolved lime solids maintained in reserve. Lime muds are classified according to excess lime content: (1) low-lime, 0.5 to 2
lbm/bbl, (2)
medium-lime, 2 to 4 lbm/bbl and (3) high-lime, over 4 lbm/bbl. All lime muds have
pH in the range of 12, and the
filtrate is saturated with lime. Fluid-loss additives include
starch, HP-starch,
carboxymethylcellulose (
CMC) or
polyanionic cellulose (
PAC).
Prehydrated bentonite can improve the
fluid loss and
rheology of a lime
mud. A maltodextrin in lime muds has been used as a
clay deflocculant, a
shale stabilizer and to increase calcium
solubility. KCl in lime muds has been another innovation for successful drilling of hydratable shales. The ability to carry very high mud
alkalinity (as excess lime) to
neutralize acid gases is one reason lime muds are used. H
2S zones can be drilled with more safety and copious amounts of CO
2 can be neutralized by a large excess of lime.