Gas hydrates are responsible for the blockage of flow lines, valves and pipelines causing loss of production and other safety consequences to the oil and gas industry. Injection of thermodynamic inhibitors such as methanol has proven to be a successful method, however the cost of recovery and possible environmental pollution by the chemicals have been a great concern. In the past two decades, increasing research has been focused on the design and evaluation of low dose hydrate inhibitors (LDHIs) to replace the traditional thermodynamic inhibitors.
In this paper, two LDHIs, Luvicap EG and Gaffix VC-713, were tested using ball stop times as a measuring parameter. The concentration effect of inhibitors, sanity and solvents on the ball stop time of each inhibitor was investigated. Results indicated that the solvent had little effect on the inhibition efficiency in the tested range of concentrations. However, the concentration of inhibitors had a strong impact on both the inhibition efficiency and the reproducibility and consistence of testing results. Rig testing provided reliable information 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 in such investigations. We concluded that the inhibition efficiency of a LDHI should be determined by both the ball stop time and its SCC. Comparison of ball stop time between two inhibitors should be made at above their SCCs.