Calcium carbonate scale in steam generator in enhanced oil recovery

摘要

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 degrees 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 (CaCO3), magnesium and iron silicate [(Mg,Fe)(3)Si2O5(OH)(4)], magnesium hydroxide [Mg(OH)(2)], and calcium and magnesium carbonate (CaCO3 center dot MgCO3) with a thickness of 1.8 to 2.3 mm adherent to a film of magnetite (Fe3O4), 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 with propargyl alcohol (corrosion inhibitor) achieved efficiency exceeding 90%.