Study of calcium carbonate scaling on steel using a high salinity brine simulating a pre-salt produced water

Abstract

In Brazilian pre-salt production, high carbon dioxide (CO2) levels in the associated gas, high salinity in the water, and high levels of calcium ions cause problems related to corrosion and scale. In practice, the scaling process already begins in the formation and near the wellbore region. However, this work has addressed this issue only on a steel surface, representing what can occur in oil production tubings and equipment since the build-up of these products in the internal walls can also impact the production flow guarantee. Parameters related to the substrate and the environment can influence calcium carbonate (CaCO3) precipitation mechanisms. In this study, the effect of steel surface roughness on calcium carbonate scaling experiments has been studied in a high salinity brine containing sodium bicarbonate (NaHCO3) and calcium chloride (CaCl2), simulating pre-salt produced water and under flow conditions. The scaling tests were carried out with a set-up composed of a peristaltic pump to recirculate the test solution through a flow cell. The scale build-up was analysed by using techniques such as Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersion X-ray Spectroscopy (EDS). For tests carried out in 3 h, the smoother surfaces had lower adhesion of calcium carbonate than surfaces with higher roughness. Lepidocrocite and rokuehnite, which are corrosion products, were formed in the substrates with higher roughness values, promoting aragonite formation. This work demonstrates that roughness influences calcium carbonate scale formation under flow conditions, besides affecting the calcium carbonate polymorphs associated with the corrosion process.