Abstract
The oil and gas industry is plagued with various flow assurance challenges including the formation of inorganic scale on component surfaces. Much research into scaling and inhibition is now being directed towards surface deposition as fouling on surfaces often causes operational problems and the rates cannot be predicted by consideration of bulk precipitation processes. However, achieving a mechanistic understanding of surface kinetics requires laboratory techniques that offer the ability to control thermodynamic parameters. A novel once-through capillary flow rig design based on the conventional tube blocking methodology was used to evaluate the surface formation of CaCO3 under dynamic flowing conditions; an important attribute of this set-up is that saturation ratio (SR) remains constant in the capillary cell due to the short residence time of the flowing brine, and conditions can be such that there is no bulk (pre-precipitated) crystals in the solution when it flows through the cell. This allows the decoupling of bulk and surface scaling, enabling the reliable assessment of the kinetics of scale deposits present in the capillaries and provides an improved mechanistic understanding of mineral scaling on surfaces. CaCO3 surface scaling kinetics was investigated by evaluating the induction times and gravimetric measurements of mass gain in the capillary cell.
Scale precipitation tests were carried out on as-received (plain) and functionalized stainless steel substrates at three saturation ratios and flow rates ranging from 10-30 ml/min. Analyses of the induction times and deposition of scale show the significant influence of flow velocity and surface wettability on heterogeneous crystallization processes, and that scale growth on surfaces is not necessarily due to the deposition of bulk precipitated crystals.
