Interpretation and theoretical modelling of inhibitor/tracer corefloods

The inhibitor squeeze process is the normal oilfield method for avoiding problems with both sulphate and carbonate scales. The dynamics of the inhibitor return curves are governed principally by the fluid rock interactions in the adsorption/desorption type treatments that are normally carried out. A particularly important function is the inhibitor adsorption isotherm and the precise form that this takes significantly affects the return curves that are observed in both laboratory coreflood experiments and in field inhibitor squeeze treatments. In this paper, a number of experimental results are presented for corefloods in outcrop sandstone cores using a phosphonate inhibitor which is frequently used in oilfield applications. These results are analysed using a theoretical procedure which is presented in the paper in order to derive the inhibitor dynamic adsorption isotherm. The form of the isotherm is then confirmed by using it in the mathematical modelling of the experiments and an excellent match to the results is achieved. The key feature that is required for long tailing in the inhibitor effluent profile is that the adsorption isotherm is very steeply rising in the low concentration region. A full discussion of the dynamics of the inhibitor return curves is presented and the significance of these results both to field inhibitor squeeze treatment sensitivities and for synthesising new improved inhibitors is explained.