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Systematic Risk Evaluation of Calcium Sulfate Formation in Production System

Scale formation is one of the flow assurance problems encountered in the oil and gas industry. It can deposit from reservoir, downhole tubing to topside facilities. Once formed, it could have a significant impact on production, including tubing and valve blockage, interference of well intervention, and even well abundance.

Calcium sulfate is one of the common scales formed in the oilfields.

Product Number: 51323-19511-SG
Author: Tao Chen, Qiwei Wang, Faisal Alrasheed, Norah Aljeaban
Publication Date: 2023
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The formation of CaSO4 mineral scale is a persistent flow assurance problem in the oil and gas
industry. To establish an effective mitigation strategy, it is essential to understand the scaling
potential and severity at different production units. In this work, the calcium sulfate scaling risk
is assessed for the entire production system, all along from seawater injection unit, production
well, surface flowline, separator and disposal well.


The results show calcium sulfate could deposit at the seawater injection well and restrict the
seawater injectability. The formation of calcium sulfate deposit could partially block the super K
zone and delay seawater breakthrough into the production well. When seawater breakthrough
occurs, the formation of calcium sulfate in the near wellbore area of the production wells could
cause severe blockage, depending on the mixing ratio of formation water and seawater,
reservoir temperature, etc. At the surface facilities, such as long flow lines and separators,
calcium sulfate can also form, especially when introducing incompatible produced waters from
different formations/reservoirs. After the separator, the mixed produced water could be finally
injected in the water disposal wells to reduce the negative effect on environment. Calcium
sulfate could deposit in the near wellbore region of disposal wells due to the higher
temperature at downhole of disposal wells and significantly reduce the injectivity.

The formation of CaSO4 mineral scale is a persistent flow assurance problem in the oil and gas
industry. To establish an effective mitigation strategy, it is essential to understand the scaling
potential and severity at different production units. In this work, the calcium sulfate scaling risk
is assessed for the entire production system, all along from seawater injection unit, production
well, surface flowline, separator and disposal well.


The results show calcium sulfate could deposit at the seawater injection well and restrict the
seawater injectability. The formation of calcium sulfate deposit could partially block the super K
zone and delay seawater breakthrough into the production well. When seawater breakthrough
occurs, the formation of calcium sulfate in the near wellbore area of the production wells could
cause severe blockage, depending on the mixing ratio of formation water and seawater,
reservoir temperature, etc. At the surface facilities, such as long flow lines and separators,
calcium sulfate can also form, especially when introducing incompatible produced waters from
different formations/reservoirs. After the separator, the mixed produced water could be finally
injected in the water disposal wells to reduce the negative effect on environment. Calcium
sulfate could deposit in the near wellbore region of disposal wells due to the higher
temperature at downhole of disposal wells and significantly reduce the injectivity.