Calcium carbonate scale in steam generator in enhanced oil recovery

This article presents a case of scale on steam generator pipe of high pressure resulting from a failure in the ion exchanger unit of the water system power supply.This generator was injecting steam into oil wells for enhanced oil recovery at a temperature and pressure of about 350°C and 17.0 Mpa, respectively.For safety and operational performance, routine inspections on the steam generator are carried out.The steam injection was interrupted by a thick layer of incrustation in a vapour injection pipe.Analysis showed a scale of calcium carbonate (CaCO 3 ), magnesium and iron silicate [(Mg,Fe) 3 Si 2 O 5 (OH) 4 ], magnesium hydroxide [Mg(OH) 2 ], and calcium and magnesium carbonate (CaCO 3 .MgCO 3 ) with a thickness of 1.8 to 2.3 mm adherent to a film of magnetite (Fe 3 O 4 ), which protects the carbon steel pipe from generated steam.To put the steam generator in safe operating condition again, the scale of calcium carbonate was removed with hydrochloric acid solution and a corrosion inhibitor.Chemical analyses and X-ray diffractometry analysis were performed in order to identify the scale formation on the inner walls of the pipe.Laboratory testing showed that acid removal with a mixture of hydrochloric acid and hydrofluoric acid with propargyl alcohol (corrosion inhibitor) achieved efficiency exceeding 90%.