The two most common oilfield scales are calcium carbonate and barium sulphate. Other scales include calcium sulphate, strontium sulphate, iron sulphide and iron (II) carbonate. Most formation brines are saturated with respect to calcium carbonate due to the presence of an excess of the mineral in almost all reservoirs. Barium sulphate is commonly encountered when highly sulphated seawater or surface waters are injected into a reservoir to maintain pressure. Mixing with high barium formation waters can lead to rapid scaling due to the very low solubility of barium sulphate in water.
The performance and action of all scale solvents depend greatly upon the conditions of application, and it is suggested that scale solvents be screened under representative field conditions.