Precipitation kinetics of calcium-phosphonate(ATMP)

Abstract

Oilfield formation damage by scale formation can occur when incompatible brine streams are mixed during production operation. Scale inhibitors are injected andretained in the reservoir by adsorption and/or precipitation. This study was divided into 2 parts: nucleation kinetics and growth kinetics and growth kinetics of scale inhibitor. A model for the induction time, the time between the establishment of supersaturation and the detection of a first precipitate, was applied to scale inhibitor (Amino tri(methylene phosphonic acid), ATMP) precipitation with calcium ions. Experimental data were analyzed by accounting for inhibitor dissociation and cation-inhibitor complexing at different ionic strength. Longer induction times were observed at lower inhibitor concentrations and in the presence of salts. The Ca-ATMP precipitates both fromed in the presence and the absence of salts had a Ca:ATMP molar ratio of 1 at a pH of 1.5 and salts did not have significant impact on the morphology of the precipitates. The presence of salts in solution was found to decrease both nucleation and growth rates in the order of LiCI<NaCl<KCl. Increases in the nucleation and growth rates delay the inhibitor precipitation kinetics which will be beneficial for effective inhibitor squeeze tratment designs and prevenation of reservoir permeability problems resulted from the precipitation in near well-bore region.