Gas hydrates phase equilibria for structure I and II hydrates with chloride salts at high salt concentrations and up to 200 MPa

摘要

Gas hydrates phase equilibria for structure I and II hydrates with chloride salts (NaCl, CaCl2, KCl and MgCl2) were measured at high salt concentrations and up to 200 MPa. The measured equilibrium data represent three-phase (Solution - Hydrate - Vapor) or four-phase (Solution - Hydrate - Salt precipitated - Vapor) equilibrium depending on the salt concentration. The hydrate phase boundary with salts was shifted to lower temperatures and higher pressures when the experimental system was below the salt saturation concentration, while the boundaries were unchanged at salt concentrations above saturation, corresponding to quadruple points. The experimental data were compared with hydrate equilibrium predictions calculated by commonly used predictive tools to assess the reliability of these tools for the brines and conditions considered. The comparison demonstrates that predictive tools exhibit large deviation to the measured data, especially at high pressures and high salinity conditions. (C) 2017 Elsevier Ltd.