Calcium carbonate had been reported in many wells at this Californian asset. All these wells used electronic submersible pumps (ESP) to assist the lift of produced fluids from the reservoir. Scale deposition was causing malfunction of the ESP pumps due to deposition on the pump internals, especially the rotor tips, causing excessive friction and ultimate failure. The temperature around the motor has been measured as 10 – 24°C higher than the bulk produced water temperature of 107 – 121°C. Previously this has not been considered during the selection of scale inhibitors. The cause of scale failures on the ESP wells has been instead attributed to the adsorption of scale inhibitor onto the sometimes significant formation fines produced from the wells.

Several scale inhibitor chemicals had been used in an attempt to inhibit deposition. Whilst general scaling in the bulk fluids seems to be under control, as indicated by the lack of scale deposits elsewhere in the well, deposition still occurred on the ESP pumps themselves. This was likely to be due to a combination of a large pressure drop in the fluids resulting in localized degassing of the produced water (below the bubble point of CO2) and also localized high temperatures on the tips of the pump rotors. Incumbent chemistries used included several different type of phosphonate chemistry.

This paper details the best-in-class chemical reselection process study to determine that the root cause failure hypothesis was correct. This included compatibility testing and scale loop testing using real produced water. The paper then goes onto detail some of the incumbent chemical treatments as well as the step change in performance realized when deployment of a newly evaluated polymeric scale inhibitor.

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