Drilling Fluids
WEL-OX P
™
Oxygen Scavenger
WEL-OX P is sodium sulphite, a soluble sodium compound
with the chemical formula Na2SO3 and a molar mass of
126.043 g/mol (heptahydrate 252.15); it is used as an oxygen
scavenger in water-based muds.
Advantages
• Reduces corrosion risk by eliminating oxygen
• Extends the temperature range of
commonly used fluid-loss-control and
viscosifying polymers
Applications
• WEL-OX P reacts with dissolved oxygen in the fluid,
eliminating a potential source of corrosion. The product is
used in all freshwater and saltwater drilling fluids except
those containing high levels of calcium or divalent brines,
in which case WEL-OX CA is used.
• The removal of oxygen also benefits polymer thermal
stability, and the use of WEL-OX P can extend the
maximum application temperature of polymers by up to
20°F (11.1°C).
Typical Physical Properties
Appearance
White solid
Specific gravity,
heptahydrate
±1.54
Solubility in water
Packaging
67.8 g/100 ml
(64°F/18°C, heptahydrate)
55-lb (25-kg) sacks
Usage
WEL-OX P is added as close as possible to the pump
suction as a dry product, at rates that depend on the oxygen
content and mud circulation rate. 2.77 ppb of sodium sulphite
heptahydrate will scavenge 1,000 ppm of dissolved oxygen.
Exact addition rates are controlled by monitoring excess
sulphite concentration in the drilling fluid at the flowline. The
recommended excess sulphite content is 100 to 300 ppm,
depending upon conditions.
Important: Bisulphite associates with calcium, which,
in the presence of oxygen, quickly converts to insoluble
calcium sulphate. Other divalent cations react similarly. As
a consequence, sulphite- and bisulphate-based oxygen
scavengers cannot be used in drilling, completion, or packer
Engineered Chemistry®
weatherford.com
fluids with high concentrations of dissolved calcium.
Where calcium values in drilling fluids are relatively
low (<800 ppm), sulphites can be used; but treatment
levels must be increased to compensate for the loss
caused by precipitation of calcium sulphate.
This product is commonly used as a food additive,
E222.
Store in a cool, dry, well-ventilated area; ensure that
packaging is completely sealed.
Consult the MSDS, safety posters, and/or product
label before use, and use personal protective
equipment as advised.
Issued December 2010
1
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