The studies were focused on evaluation of different scale dissolvers for barite sag or barium sulfate scales, while the chemically similar compound, the strontium sulfate obtained much less attention. Therefore, an extensive research programme was launched with the aim at evaluating the potential of seven different polyamino carboxylic acids (NTA, EDTA, DCTA, DTPA, EGETA, HEDTA and TTHA) using both technical and economic aspects to compare the behavior of these two compounds.

Dissolving capacity of each compounds was determined under equilibrium conditions as a function of BaSO4 and SrSO4 concentration in both the presence and absence of reservoir rock. The absolute and relative selectivity of dissolution were precisely analyzed. Dissolution of all components was followed in time and kinetic calculations were made. Results of the measurements provided reliable data for comparison of dissolution capacities under identical chemical conditions.

On the basis of the experimental findings it was concluded that the sequence of dissolution capacity is different if the results were evaluated in technical or economic sense. It was also shown that the preferentially used compounds (e.g. DTPA, and particularly EDTA) are not the best choices when technical considerations are only enforced. Namely, the practice justifies their application at the expense of poor efficiency. Results of that systematic analysis may open new vistas in mitigation of formation damage caused by BaSO4 or SrSO4 and accelerate the search for more effective mixtures of complex-forming dissolvers.

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