The injection of multiple chemicals, such as anti-scale and anti-corrosion additives, must often take place sequentially or simultaneously in very close injection points. Thus it is necessary not only to evaluate the efficiency of chemicals individually, but also to screen for incompatibilities and/or interference between chemicals. These interferences can affect either the anti-scale efficiency, the anti-corrosion efficiency, or even worth both additives efficiencies at the same time. This kind of mutual reduction of efficiency may have been the reason for past pipeline failures, where both scaling and corrosion were observed despite the addition of large quantities of both additives. Electrostatic interaction is a possible explanation, as the two chemicals carry opposite charges. In conjunction with the usual tests performed for additive selection, a physicochemical framework has been developed to evaluate the behavior of pairs of additives at different concentrations. For a model water presenting both corrosion and scaling issues, the efficiency of the anti-scaling additive is evaluated based on the quantification of free Ba2+ in solution by ionic chromatography and the efficiency of the anti-corrosion additive is assessed based on the change in the interfacial tension. Many candidate additives for oil field applications have been evaluated and "interaction maps" have been constructed. These maps indicate regions of concentrations at which one or both additives are not effective. These maps are useful for the selection of products that should be effective without risks of interactions. To finalize the validation, we can perform an "ultimate" blocking test where both additives, water and oil, are in contact at one point of the experiment, to also take into account the partitioning of additive between oil and water. This framework is not only useful for production chemistry studies of new field developments, but also for new product tenders in existing fields.

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