Estimating the Hydrate Safety Margin in the Presence of Salt and/or Organic Inhibitor Using Freezing Point Depression Data of Aqueous Solutions

Abstract

Developing systematic methods for controlling and monitoring gas hydrate risks along the pipeline and/or downstream conditions could provide the solution for future challenges. In this paper, the possibility of predicting the hydrate suppression temperatures of fluids from freezing point depression data of aqueous solutions containing different concentrations of salt and/or non-hydrate-forming organic inhibitor is investigated by developing a general correlation. The developed correlation considers only the changes in the freezing point of the aqueous solution, and there is no need for the analytical composition of the aqueous solution. Since measurement of the freezing point for the aqueous phase is much easier than measuring the hydrate dissociation point, such a relation can reduce the experimental costs. A well-proven thermodynamic model is used for generating pseudoexperimental data of hydrate suppression and freezing point depression for 160 different aqueous solutions containing various salts and/or organic inhibitors over a wide range of concentrations in order to develop this correlation. To examine the reliability of this model in predicting the freezing point depression, some experimental freezing point depression data are measured and compared with literature data and the predictions of the model. Independent data are used to examine the reliability of this method. The predictions of this approach are in acceptable agreement with the independent experimental data, demonstrating the reliability of this predictive method.