Drilling Fluids
Gypsum
Gypsum is a soft mineral composed of calcium sulfate
dihydrate (CaSO4·2H2O), which is ground to a fine powder.
Molar mass (dihydrate) is 172.172 g/mol.
Advantages
• Widely available, economical source
of calcium
Applications
• Gypsum is the base material for gypsum-based drilling
fluids that are designed to convert smectitic clays by ion
exchange to their calcium form and thereby limit their
hydration and swelling. The sparingly soluble nature
of calcium sulphate serves to provide a limited supply
of calcium ions in gypsum muds without the high pH
associated with lime.
• Gypsum can also be used to reduce soluble carbonates,
again through the provision of calcium that precipitates
soluble carbonate ions as insoluble calcium carbonate.
Typical Physical Properties
Appearance
White powder
Density,
dihydrate
2.32 SG
Density,
anhydrous
2.96 SG
Bulk density
26.8 lb/ft3
430 kg/m3
Packaging*
110-lb (50-kg) and 55-lb (25-kg) sacks
1-MT big bags
*These packaging options are typical, but a range of packaging is available to
suit operational needs.
Usage
Gypsum need only be present at a concentration that is in
excess of its solubility limit in a particular medium. Solubility
in water is 0.15 lb/ft3, or 2.4 kg/m3, (68°F/20°C, dihydrate)
and reduces with increasing temperature; therefore a
concentration that is greater than that value will suffice.
Typical values used in field fluids range from 2 to 5 lb/bbl
(5.7 to 14.3 kg/m3).
For carbonate removal, the degree of contamination
determines the additive concentration.
Consult the MSDS, safety posters, and/or product label
before use, and use personal protective equipment
as advised.
Issued March 2010
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