Influx of gases is one of the main causes of corrosion failures in completion and packer fluids. The most destructive gases are carbon dioxide (CO₂) and hydrogen sulphide (H₂S), which can leak into the wellbore along with other reservoir gases, and oxygen (O₂) that enter the fluid during circulation at the surface, or in the case of packer fluids, during annular pressure bleed-off operations. This section of the manual presents the detailed chemistry of what happens when acid gases, such as carbon dioxide and / or hydrogen sulphide, enter into buffered formate brines. The carbonate / bicarbonate buffer is shown to buffer the brine at two pH levels, 10.2 and 6.35, and even after a massive acid gas influx, pH can never drop to a value lower than around 6. Formate brines are the only high-density brines compatible with the alkaline carbonate / bicarbonate pH buffers, and therefore the only heavy brines that are capable of protecting themselves against such large influxes of acid gas. The section also discusses the beneficial properties of formate brines, which protect against damage caused by oxygen.

 

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