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.
The formation of scale and oil & gas go hand in hand, it is a natural consequence of handling water associated with crude oil production.1 Scales can build-up anywhere from clogging wellbore area to surface facilities such as production tubings, valves (subsurface control valves, SSCV), fouling pumps (electrical submersible pumps, EPSs) amongst many others; thereby restricting fluid flow and posing significant operational costs.2 Dealing with damage as a result of inorganic scale formation is one of the major oil and gas industry challenges costing hundreds of millions of dollars per year in lost production in emergency shutdown, equipment failures or maintenance costs, and reduction in production.1, 3 The inability to properly predict the severity ensures the industry spends millions of dollars in preventing and removing scale formation.4, 5 There are various studies on the precipitation and deposition of inorganic scales, particularly calcium carbonate (CaCO3). Most of these past studies on scale deposition and predictive models are mainly focused on the thermodynamic parameters in the bulk with little attention paid to scaling on surfaces, hence there is little reconciliation between bulk precipitation and surface deposition.
