Estimating the hydrate stability zone in the presence of salts and/or organic inhibitors using water partial pressure

Abstract

Hydrate characteristics of an aqueous system could be related to water activity/fugacity for many practical purposes with a reasonable accuracy. In this work, the possibility of using vapour (or partial) pressure of aqueous solutions for estimating the hydrate stability zone has been investigated. Following that, a new correlation has been developed for estimating the hydrate stability zone of various fluid systems in the presence of salts and/or organic inhibitors. The correlation is based on the assumption that the changes in the water properties due to the presence of salts and/or organic inhibitors play the main role on the hydrate characteristics of aqueous systems. The developed correlation relates the hydrate inhibition characteristics of aqueous systems to the changes in the water partial pressure due to the presence of salts and/or organic inhibitors. It takes into account the effect of hydrocarbon phase and/or hydrate structure by introducing the hydrate dissociation pressure at a given temperature in the presence of distilled water. The correlation has been developed using the predicted hydrate phase boundaries for 10 fluid systems generated by a well-proven comprehensive thermodynamic model. The correlation has been used for predicting the hydrate stability zones for 19 independent fluid systems. The results are compared with the available experimental data, demonstrating the reliability of the newly developed correlation.