Specific critical concentrations of low dosage hydrate inhibitors in a THF–NaCl hydrate formation solution

Abstract

Hydrate formation and its attendant problems are well known in the oil and gas industry. The desire to reduce the costs and environmental impact of traditional hydrate inhibitors has led to a focus on the design, development and evaluation of novel and environmentally friendly low dosage hydrate inhibitors (LDHIs). In this study, two LDHIs, namely Luvicap® EG and Gaffix® VC-713, were tested using tetrahydrofuran (THF) as a hydrate promoter and a ball-stop rig. The ball stop-time was used to determine the inhibition efficiency. The concentration effect of inhibitors, salts and solvents on the ball-stop time was investigated. Results indicated that the inhibition efficiency of an inhibitor is sensitive to the micro-environment of the THF-hydrates activities which includes the concentration and types of these additives. The reproducibility and consistency of the test results were also largely dependent on the concentration of inhibitors. Reliable information was provided only if the concentration of the inhibitor was above a critical concentration, below which the testing results scattered drastically and were inconsistent. As the critical concentration was inhibitor-dependent, a specific critical concentration (SCC) was proposed which is the first reported in such investigations. We concluded that the inhibition efficiency of an LDHI should be determined by both the ball-stop time and its SCC. Comparison of ball-stop times between two inhibitors should be made above their SCCs. Salt and solvent concentrations and other additives present in the operating systems should also be considered when a suitable LDHI concentration is determined for a particular field application.