Calcium carbonate scale formation - assessing the initial stages of precipitation and deposition

Scale formation is a serious problem encountered in many industries including oil or gas production, water transport, power generation and batch precipitation. Normally, studies of scale formation have been focused on precipitation processes in the bulk solution using bulk jar methods where the precipitation tendency rate and inhibitor effectiveness are quantified. Several recent studies have started to focus on scale deposits formed on the surface of metals. In this paper, calcareous scale formation was studied both in the bulk solution and on the metal surface in three supersaturated scale formation solutions which represent typical waters encountered in oil and gas production. An electrochemical technique, using a rotating disk electrode (RDE), was used to quantify scale formation on the metal surface. With this technique, reduction of oxygen was considered at the surface of a RDE. The rate of oxygen-reduction at the surface of the RIDE enables the extent of surface coverage of scale to be assessed. To understand the formation and growth of the surface scale deposit, surface analysis was used in conjunction with this technique. Scanning electron microscopy (SEM) was used for analyzing the microstructure of the scale. At the same time, inductively coupled plasma (ICP) was used for analyzing the quantity of the precipitate formed in the bulk solution and scale formed on the metal surface by dissolving the scale. In this paper it is demonstrated that bulk precipitation and surface deposition have different dependencies on the index of supersaturation and so to completely understand an industrial scaling system both processes should be studied. (c) 2005 Elsevier B.V All rights reserved.