Principal Additives of Lime Muds

Lime or lime-treated muds generally contain native or commercial clays, caustic soda, organic defloc-culants, lime (as a source of calcium), and a fluid loss control agent. Principal additives of lime muds are listed in Table 6.

Table 6

Principal Additives of Lime Muds

Additive

Concentration, lb/bbl

Function

Bentonite

22 - 26

Viscosity, Filtration Control

Lignosulfonate

2 - 6

Deflocculant

Lime

2 - 1Q

Inhibition, Alkalinity Control

Caustic Soda/Caustic Potash

for pH 1Q.5 - 12.5

Alkalinity Control, Inhibition

Lignite

2 - 4

Filtration Control

Starch

S - 4

Filtration Control

Vpac

Q.25 - 1.5

Filtration Control ^

Bentonite - Bentonite is added for viscosity and filtration control. Because sodium is replaced by calcium when the mud is "broken over" to a lime mud, the bentonite must be prehydrated in fresh water before adding it to the active system.

Lignosulfonate - Lignosulfonate is added as a deflocculant and for filtration control. In areas where chrome lignosulfonates are prohibited, calcium lignosulfonates such as Lignox and Setan can be used without compromising performance.

Lime - Lime is added to increase PM. Excess lime is usually maintained in the range of 2-4 lb/bbl. Excess lime is a measure of the alkalinity reserves that are available to go into solution as drilling proceeds and calcium and hydroxyl ions are depleted.

Caustic Soda/Caustic Potash - Caustic soda or caustic potash are used to control filtrate alkalinity (PF). Controlling filtrate alkalinity will in turn control the solubility of lime and stabilize rheological properties.

Lignite - Lignite is added for filtration control; however, lignite in the presence of soluble calcium forms a calcium salt of humic acid precipitate. At elevated temperatures, lignite degrades to form carbonates.

Starch - Starch can be added for filtration control up to mud temperature of 250°F. The high alkalinity of the mud filtrate will prevent fermentation. Thus, a biocide is not usually required.

Polyanionic Cellulose - PAC is used to control filtration provided that the calcium ion concentration does not exceed 400 mg/L. PAC can also provide supplemental viscosity and encapsulation of solids. For mud densities less than 12 lb/gal, regular viscosity can be used; however, as density increases low-viscosity PAC should be used to avoid excessive viscosities.

Other Additives - Gilsonite, asphalt, cellulosic fibers are added to seal permeable formations and stabilize the wellbore.

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Responses

  • lisa
    What does lime do to the rheological properties of drilling fluids?
    7 years ago
  • Darcy
    Does lime change the rheological properties of a drilling fluids?
    6 years ago
  • amerigo fiorentino
    What dies excess lime measure in oil mud?
    4 years ago
  • birikti
    Does lime affect bentonite in drilling fluids?
    4 years ago
  • lori
    Does lime in mud increase viscosoity?
    2 years ago

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