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Amonyum Bisülfit

SCAV OXN

Description

DDC-SCAV OXN is a concentrated solution of sodium bisulphite used as an oxygen scavenger in water-base fluid systems.

Typical Properties

Appearance : Pale yellow liquid
pH (neat) : 4.0 - 5.0
Specific Gravity : 1.25-1.35

Features and Benefits

DDC-SCAV OXN removes dissolved oxygen in water-base systems which causes severe corrosion in the drill string and surface equipment at very low concentrations (<1 ppm) under most circumstances. It reacts with oxygen as follows

4NaHSO3 + O2 → 2Na2SO4 + 2H2O + 2SO2
SO2 + 2NaOH → Na2SO3 + H2O
2Na2SO3 + O2 → 2Na2SO4

DDC-SCAV OXN is compatible with all types of water-base drilling, workover and completion fluids except calcium and zinc brines .

DDC-SCAV OXN also extends the thermal stability of polymers commonly used in water-base drilling fluids.

Application

DDC-SCAV OXN is added to eliminate dissolved oxygen in water-base fluids to inhibit pitting type corrosion detrimental to the drillstring and surface equipment. It should be injected continuously and evenly into the pump suction through a corrosion resistant metering pump during circulation. DDC-SCAV OXN can be injected into the downhole fluid with minimal atmospheric contact and therefore this technique minimizes the rapid depletion of DDC-SCAV OXN by atmospheric oxygen.

Limitations

DDC-SCAV OXN does not perform in fluids with high calcium and zinc content and is thus incompatible with calcium and zinc brines. It can be used in fluids containing calcium less than 2,000 mg/l.
DDC-SCAV OXN is also incompatible with bactericides containing aldehydes. Otherwise, the effects of both chemicals would be diminished.
DDC-SCAV OXN should not be mixed with caustic soda. This results in explosion of released Sulfur Dioxide gas.
At high pH levels, DDC-SCAV OXN decomposes and releases Sulfur Dioxide gas.

Treatment

Initially, DDC-SCAV OXN is injected at a rate of 0.005 to 0.01 gal/bbl at the pump suction.
A DDC-SCAV OXN concentration of approximately 8 mg/l removes 1 mg/l of dissolved oxygen. Normally, treatment is designed to maintain DDC-SCAV OXN/ Oxygen ratio of 1:10 on a weight basis to provide a slight residual in the system as a safety margin. A sulfite concentration of 75 to 150 mg/l is recommended at the flow line. If calcium content of filtrate is greater than 200 mg/l, sulfite level should be kept around 40 mg/l.
Over treatment with DDC-SCAV OXN increases the corrosivity of the system as well as promoting calcium or barium sulfite precipitation.

Packaging

DDC-SCAV OXN is supplied in 85 kg drums.