Zinc Carbonate

Under operating conditions, zinc carbonate reacts with sulfides to form zinc sulfide (ZnS), which has an extremely low solubility in water (0.0096 g/mL). Drilling fluids should not be acidified; otherwise, hydrogen sulfide could be liberated.

zinc carbonate is effective as a scavenger at the pH levels found in drilling fluids. It is recommended that a pH above 10 be maintainedb whenever H2S is expected. This high alkalinity converts the dangerous H2S gas to less toxic bisulfide (HS-) and sulfide (S2-) ions. The alkaline pH (>10) allows an extra margin of safety.

The initial treatment of zinc carbonate is usually 1.5 to 3 lb/bbl (3.75 to 8.0 kg/m3), depending on requirements. Subsequent field treatments should be based on approximately 1 lb/bbl (2.85 kg/m3) of zinc carbonate per 800 mg/L of sulfides detected.

One hundred kilograms (kg) of zinc carbonate reacts with approximately 25 kg of hydrogen sulfide. Use a Garrett Gas Train and proper Dräger tubes to measure the sulfide content. Zinccarbonate scavenger should be added through the hopper.

The product has a fine particle size and good dispersibility which minimizes reaction time. The use of excessively high pH (>11.5) should be avoided when using zinc carbonate scavenger in water-base fluids, as extreme viscosity increases are likely.
• Is not pH-dependent; it is effective at alkaline pH, such as 10 to 11, whereas iron materials are less so
• Helps remove the hazard of dangerous H2S gas escaping to the surface
• Lessens the possibility of hydrogen embrittlement occurring on downhole tubulars
• zinc carbonate can be used in oil- and synthetic-base fluids, but pilot testing is recommended