Calcium sulfate scale: A review of state-of-the-art

Precipitation of sparingly soluble salts is a common issue in water treatment processes and oil and gas production systems. Precipitation occurs when incompatible brine mix and operating parameters like pressure, pH, temperature, etc. change. This may lead to decreased production output, equipment failure, and a decline in process efficacy. Of the many different types of scales known to exist, the calcium sulfate scale is particularly challenging to deal with as CaSO₄ is practically insoluble in hydrochloric acid, which is used to remove other types of scales, such as carbonate scales. Although numerous initiatives to inhibit calcium sulfate precipitation have been documented in the literature, it remains largely an issue. This review offers a critical analysis of the state-of-the-art regarding calcium sulfate scaling, exposing its mechanisms of precipitation, inhibition, and methods for mitigating its effects. The limits of current technologies and further research areas are also highlighted in this review.