Understanding of the Co-deposition of Calcium Sulphate and Calcium Carbonate Deposition in ESP

摘要

Electric Submersible Pump (ESP) in oilfield is prone to scale deposition, largely due to temperature increases by motor heating, and turbulent flow and high shear inside of pump. In this work, the formation of calcium sulphate and calcium carbonate were studied under a range of conditions that could possibly be encountered in ESPs. The produced water chemistry changes from 100% formation water to mixed formation water and injected seawater over time. The scaling tendency and potential mass deposition are simulated using a thermodynamic prediction model. Dynamic scale loop tests were carried out to study the calcium carbonate, calcium sulphate and co-deposition under field conditions. The results indicate that the risk of calcium carbonate scale at the initial stage of production in both downhole and ESP. With the breakthrough of seawater, the risk of calcium sulphate scale increases, and harsh calcium sulphate scale could form in ESP. This study also suggests that the interference between CaSO_4 and CaCO_3 formation is minor under the test conditions. These findings will be used to develop the scale mitigation strategies.