Calcium Carbonate Scale Deposition Kinetics on Stainless Steel Surfaces

Calcium carbonate scale is one of the most common inorganic scales which deposits on the surface of oil and gas production facilities. This causes significant loss of production and ultimately leads to shut down of production lines if not properly managed. There has been a great amount of research on calcium carbonate deposition studies, but most of these studies have been on understanding calcium carbonate bulk precipitation process. However, little attention have been made on calcium carbonate surface deposition mechanism, which is the main challenge in mitigating scaling in oil and gas and desalination industries. Understanding the mechanism of its formation at different environmental conditions and using a methodology that would reflect the field scenario will gives information required for a reliable predictive model. This study investigated calcium carbonate surface build-up under flow conditions, across a wide range of saturation ratio (SR) at 25oC and 70oC respectively. Both bulk induction time (tind) and surface induction time, which is referred to as scaling time (ts) were determined from capillary flow rig experiments. Mineral scale surface fouling was monitored by a sensitive differential pressure technique with respect to build up of scale on the wall of the capillary cell resulting to change of pressure across the test capillary cell. It was found that, two scaling regimes occur within the brine composition investigated. At SR < 80, surface fouling is controlled by nucleation and growth, while at SR > 80, is controlled by the adhesion of pre-precipitated crystals. This result was supported by the turbidity measurement and inductively coupled plasma mass spectrometry (ICP-MS) analysis. The calcium carbonate growth rate determined by measuring the amount of scale deposited at the surface of the capillary cell by Inductively coupled plasma mass spectrometry analysis (ICP-MS) was smaller compared to the amount of scale predicted from Hagen Poiseuille (HP) equation, where the growth rate is estimated from the pressure drop across the capillary cell as scale build up on the wall of the capillary cell. This was attributed to non-uniformity of the scale layer along the capillary cell which is omitted in the HP equation. A semi empirical model has been developed from the experimental work, which can predict scale deposition growth rate over a period of time and as a function of deposition flux at a given temperature.