Over the past 10 years significant improvements in "green" scale inhibitor chemistries have led to considerably increased use in certain regions, notably the Norwegian sector of the North Sea. However, the use of these more environmentally acceptable products can be at the cost of optimum performance. This was the case for the Varg field: an extensive Best-In-Class re-selection of available yellow / green polymeric inhibitors failed to achieve the required improvement in lifetimes. Modelling work conducted for one of the wells had also shown that one of the primary causes of the poor lifetimes was the lack of effective placement of the treatment chemical in the water-producing zones.1 More recent experimental work to be described in this paper has demonstrated that the scaling challenges on this field could be mitigated in part by adopting the less environmentally friendly, but better retaining, ‘red’ phosphonate chemical. Comparison of the predicted inhibitor return profile using laboratory derived data with the subsequent field return showed very good correlation in a well with no placement challenge. In a manner analogous to the polymer-based chemistries,1 application of the phosphonate inhibitor in a well with known placement issues gave less impressive return lifetimes. However the better retention properties meant that the treatment lifetimes remained acceptable despite the poor placement. When the placement issues were taken into account, the previously derived isotherm proved very effective at simulating the field case in this more challenging well. This paper therefore describes an alternative, more rigorous approach to simulating treatments in challenging wells rather than using history matched averaged field return isotherms. The paper then shows the impact on optimisation of future treatments when the different approaches are examined. This work therefore expands considerably on that previously described in SPE 114077.