The data in literature clearly proved that the polyamino carboxylic acids (PACAs) are promising barite dissolvers. So far, however, only the ethylene-diamin-tetraacetic acid (EDTA) and the diethylene-triamin-pentaacetic acid (DTPA) were studied and tested in detail. Therefore, an extensive research programme was launched to compare the potential of other barite dissolvers. The laboratory study were also extended to nitrilo-triacetic acid (NTA), diamino-cyclohexane-tetraacetic acid (DCTA), dioxaoctamethylene-tetraacetic acid (DOCTA), hydroxyethylene-diamin-triacetic acid (HEDTA) and triethylene-triamin-hexaacetic acid (TTHA).

Dissolving capacity of each compounds was determined as a function of concentration for barite and reservoir rocks. The absolute and relative dissolution selectivity and the matrix effect of formation rocks were precisely analyzed. Independent variable of the measurements was the pH and type of organic acids used as complex-forming promoters. In the batch type studies oxalic acid (OXA), malonic acid (MOA), maleic acid (MEA), succinic acid (SUA) and tartaric acid (TARA) were tested. It was concluded that the performance of well treatment methods (mitigation of formation damage, removal of barium sulfate scales, etc.) based on application of polyamino carboxylic acids can significantly be increased by adding sodium (potassium) hydroxide to the complex-forming agents and setting its concentration to optimal level. Application of organic acids jointly with polyamino carboxylic acids, however, could not be justified if the dissolver system had already been optimized by alkali addition. Thus, from practical point of view it has to be emphasized that optimization of barite dissolving methods by pH regulation is much more efficient and cost-effective than adding multi-functional organic

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