Evaluation of Silica and Related Matrix Ion Effects on Common Scale Inhibitors

Abstract

Scale inhibitors have been widely used to solve the mineral scale problems in various energy industries. The performances of scale inhibitors are influenced by different species (such as ion or chemical species) in the produced water. Silica species, one of the most ubiquitous species in the produced water, are present either by the form of silicic acid or divalent ion silicate complex/interactions (e.g., Ca,Mg silicate and Fe(II) silicate). Their impacts on common scale inhibitor performance, however, have not been systematically studied. In this study, the effects of silica and the related divalent ion silicate on the several common scale inhibitors were investigated by examining the crystallization and inhibition kinetics of barite. The results show that the presence of silica or divalent ion silicate does not show a significant effect on barite crystallization or inhibition efficiency of the polymeric inhibitors. The presence of Ca2+ and Mg2+ ions with high concentrations (e.g., 16 000 mg/L Ca2+ and 2000 mg/L Mg2+) or Fe2+ ions (e.g., 10–15 mg/L Fe2+) shows detrimental impacts on the phosphonate inhibitor diethylenetriamine penta(methylene phosphonic acid) (DTPMP). Further experimental results show that the presence of Ca,Mg silicate complex/interactions does not change the impacts of Ca2+ and Mg2+ on DTPMP, while the formation of Fe(II) silicate complex/interactions helps to partially recover the detrimental impacts of Fe2+ on phosphonate inhibitors. The mechanism of Fe(II) silicate influence on barite inhibition with DTPMP was studied by measuring the Fe2+, silica, and DTPMP concentrations in the aqueous phase before and after the experiments. The results indicate that this phenomenon is due to the Fe2+ competition between forming Fe(II)–DTPMP precipitates with DTPMP and forming Fe(II) silicate complex/interactions; silica is over 50 times higher in concentration than DTPMP. More Fe(II) silicate interaction results in less Fe(II)–DTPMP formation and more DTPMP available as scale inhibitors. Such observations inform the impact of the widely present silica species on scale inhibitor performances and provide valuable insights in oilfield scale management.