Experimental Investigation of the Weakening Effect of Corrosion Inhibitors on the Performance of Kinetic Hydrate Inhibitors

Gas hydrate blockage and metal corrosion are both crucial flow assurance issues in the oil and gas transportation pipelines, and kinetic hydrate inhibitors (KHIs) and corrosion inhibitors (CIs) are commonly used to deal with the challenges. In this study, the effect of four CIs and the mixed inhibitor formulation of CIs and KHIs were both studied on the kinetics of methane–propane hydrate formation, while interfacial tension and zeta potential characterization were conducted to deeply investigate the interactions between CI and KHI fractions. Results demonstrated that the CI applied in experiments all had a limited impact on hydrate growth at low concentrations but possessed various effects at higher concentrations, which were closely related to the type of CI. When mixed with KHI, CI with a high concentration can effectively weaken the inhibition performance of KHI, while the overall inhibition capacity of the mixed inhibitor formulation on hydrate formation was not the simple sum of the single CI and single KHI. The weakening effect of the selected CI on KHI was attributed to two mechanism hypotheses. On the one hand, CI might compete with KHI in the areas where KHI mainly acts to inhibit hydrate formation, such as the gas–liquid interface and the adsorption sites near the hydrate surface. On the other hand, KHI molecules can combine with CI molecules through electrostatic attraction when the electronegativity of a mixed inhibitor formulation is opposite that of a single KHI, which probably results in the loss of inhibition function of these KHI molecules on hydrate formation. The overall results also indicated that water-soluble imidazolinamide was a potentially applicable CI that can be used together with KHIs because of their good compatibility in inhibiting hydrate formation.