Control of inorganic sulphate and carbonate scales with polymer, phosphonate and phosphate ester scale inhibitors is well established within the oilfield service industry. The environments in which these chemicals work best have been published, i.e., vinyl sulphonates are very effective for sulphate scale control in low temperatures (Laing and Graham 2003) whereas phosphonates are much less effective under these same conditions but improve at higher temperatures (Jordan et al., 2016). 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 evaluation of a North Sea produced water (1,500ppm Bicarbonate, 30ppm Iron and 3,550ppm Calcium ions) will be outlined where a very high carbonate saturation ratio exists within a produced fluids heater resulting in very high inhibitor treatment rates of a MEA phosphonate type scale inhibitor). Dynamic tube blocking tests were carried out to evaluate nucleation inhibition of a range of single component inhibitors before blends of these chemicals including biopolymer/phosphonate and poly aspartic acid/phosphonate where evaluated try to reduce the inhibitor concentration required to control scale formation.

For this challenging carbonate scale environment at a temperature (105°C), it was observed that a biopolymer/currently applied MEA phosphonate blend was more effective than either of the components by themselves, suggesting synergistic interaction. Environmental properties of the inhibitors evaluated played a key role in their selection and has resulted in trial of polymer/currently applied phosphonate being planned for this field. Qualification test results for the incumbent, potential replacement single inhibitor actives and blended inhibitor are presented.

The current regulatory challenges with REACH 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 molecule development.

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