Synergistic Scale Inhibitor Blends Provide Enhanced Carbonate Scale Management- Laboratory to Field

Abstract

Control of inorganic sulphate and carbonate scales with polymer, phosphonate and phosphate ester scale inhibitors is well established within the oilfield service industry. Less well understood is the potential for synergistic interactions with blends of polymers/phosphonates/phosphate esters to give reduced treatment rates, lower chemical discharge volumes and potentially lower treatment cost specifically for carbonate scale control. In this paper selection and field trial application of such a synergistic blend is presented to control severe scaling within produced fluid heaters on a North Sea platform. Dynamic scale loop (DSL) tests were carried out to evaluate inhibition of a range of single component inhibitors before blends of these chemicals including biopolymer/phosphonate and carboxylic acid functionalized polymer/phosphonate 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 (milder sulphate) scale environment at high temperature (105°C), it was observed that a blend of a polymer (carboxylic acid functionalized polymer) and currently applied low molecular weight 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 products injection rate for 1 week with differential pressure across the production and test heaters carefully trended (along with fluid flow rate and fluid heating performance) 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 incumbent chemical being reinstated to allow review of the trial formulations performance. Along with differential pressure trending scaling ions, suspended solids assessment via environmental scanning electron microscope (ESEM) and measurement of inhibitor concentration within the produced water was carried out to ensure scale control was effective. The current regulatory challenges with REACH (registration, evaluation, authorization and restriction of chemicals) mean that the methods outlined in this study offer the potential to reduce chemical treatment rate, cost and environmental impact by evaluating the synergistic interaction of the current range of commercially available environmentally suitable scale inhibitors and therefore eliminating the very high registration costs/ time delays to the market associated with new inhibitor molecule development.