Evaluating chemical-scale-inhibitor performance in external magnetic fields using a dynamic scale loop

Abstract

Monoethylene glycol (MEG) is extensively used in oil and gas pipelines to prevent the formation of gas hydrates. However, the injection of MEG may inadvertently contribute to mineral-ion precipitation through reduced solubility of ionic species and operation under alkaline conditions for corrosion control. As a result, the injection of chemical scale inhibitors (CSI) to manage scaling is often required. Non-chemical inhibitors, such as external magnetic fields (MFs) have also been shown to inhibit scaling in aqueous solutions. With this in mind, we investigated the combined application of CSIs and MF treatment to study the formation of scale under conditions representative of a MEG regeneration system's reboiler, a system under a high risk of scale formation. Two commercial CSIs were examined in the presence and absence of a 0.650-T external MF using a dynamic-scale-loop device. The CSIs were injected into ionic solutions containing 1656.9 ppm calcium ions and 2628 ppm carbonate ions in aqueous MEG (80 vol%), and experiments were performed at 130 °C and pH 9.5. Despite the presence of a CSI, the MF promoted scale formation and afforded a stable calcium carbonate phase morphology at high MEG concentrations. Moreover, the zeta potential under the applied MF was lower than that in the absence of the MF, which led to greater scaling, implying that the magnetic field had an ionic interfacial effect. These results provide significant insight into the effect of a MF on scale formation, irrespective of the use of a CSI, and help to interpret the effects of various treatments for scale removal or the prevention of scale formation during the MEG regeneration process.