Synergistic Scale Inhibitor Blends for Severe Carbonate Scaling Systems

Abstract

Control of inorganic sulphate and carbonate scales with polymer and phosphonate based scale inhibitors is well established within the oilfield chemical industry. The potential for synergistic interactions with blends of these chemical types to give reduced treatment rates, lower chemical discharge volumes and potentially lower treatment cost specifically for carbonate scale control and better energy efficiency, is less well understood. This paper presents the selection and field trial application of such a synergistic blend designed to control severe scaling within produced fluid heaters on a North Sea platform, however this blend has the potential to be applied in other environments such as CO2 WAG production systems, heaters and heat exchangers, for example. Inhibitor performance tests were carried out to evaluate inhibition of a range of single component inhibitors before blends of these chemicals were evaluated to try to reduce the inhibitor concentration required to control both calcium carbonate (saturation ratio, SR 550, mass 1100mg/l) and barium sulphate (SR 55, mass 450mg/l) scale formation. For this challenging carbonate scale environment at high temperature (105°C), it was observed that a blend of a polymer (carboxylic acid functionalized polymer) and the currently applied phosphonate was more effective than either of the components by themselves, suggesting synergistic interaction. Results from the initial field trial of the synergistic blend are presented with monitoring methods outlined to confirm that the formulation is as effective as the laboratory evaluated tests suggested. The initial trial started at the incumbent product injection rate for 1 week with differential pressure across the topside heaters, fluid flow rate and fluid heating performance being trended to confirm scale control prior to a 20% reduction in treatment rate being applied for 1 week with a further reduction of 40% of the incumbent being applied for another 7 days prior to the full dose rate of the incumbent chemical being reinstated to allow full review of the trial results. The methods outlined in this study demonstrate the potential to reduce chemical treatment rate, cost and environmental impact by evaluating the synergistic interaction of the current range of commercially available scale inhibitors and therefore eliminating the high registration costs and time associated with bringing a new molecule to market. This study also offers the potential for synergistic blends to be utilized to inhibit severe carbonate scales in challenging environments including extreme calcite scaling environments such as CO2 WAG production, high temperature topside heaters, alkaline surfactant polymer flooding and heat exchangers.