Relationship between the gas hydrate suppression temperature and water activity in the presence of thermodynamic hydrate inhibitor

Hydrate formation and blockage in deepwater oil and gas operations can be prevented by using thermodynamic hydrate inhibitors (THIs). The presence of THIs changes the hydrate suppression temperature; therefore, predicting the change in the hydrate suppression temperature is critically important. In this study, the water activity of eight THI solutions at different concentrations was measured, and the relationships between the hydrate suppression temperature and water activity were analyzed. The analysis results show that the linear, quadratic and cubic polynomials precisely describe the relationship between the hydrate suppression temperature and water activity of the THI solution, as confirmed by the coefficient of determination (R-2) value higher than 0.99. Interestingly, the hydrate inhibitory effect increases linearly with decreasing water activity of the THI solution. Based on the existing hydrate suppression temperature correlation, the linear and quadratic polynomials for expressing the relationship between the hydrate suppression temperature and water activity for eight THIs at different pressures were obtained. The data for all eight THIs investigated in this study were collectively analyzed, indicating that at a certain pressure, the hydrate suppression temperature mainly depends on the water activity of their aqueous solution, and these parameters have a linear relationship, irrespective of the THI used. Furthermore, the general correlations for expressing the relationship between the hydrate suppression temperature and water activity for THIs are proposed. This study can provide a simple method for estimating the hydrate suppression temperature of the fluid system using water activity under deepwater conditions.