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.
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.1,2
Calcium sulfate is one of the common scales formed in the oilfields. Calcium sulfate scale is usually formed due to mixing of incompatible waters, i.e., waters containing high calcium (such as calcium rich formation water in carbonate reservoirs) and high sulfate waters (such as seawater or sulfate rich produced water from reservoirs flooded with seawater). It also could form when the saturation of scaling water increases to a certain level due to the change of operation conditions, especially for the increase of temperature. Calcium sulfate can form in the reservoir, near wellbore area, production tubulars, topside facilities and produced water re-injection wells.3-6
