Phase equilibrium data of methane hydrates in mixed brine solutions

Abstract

Knowing the hydrate phase equilibria in brines is critically important to assess the risk of hydrate formation, especially for conditions involving high salinity and very high pressure, which are becoming more prevalent in oil/gas exploration and production. Hydrate phase equilibria data for mixed salt brines over a wide range of pressure is very limited in the open literature. Inorganic salts are thermodynamic hydrate inhibitors and are commonly present in produced water from oil/gas production. As such, this study reports methane hydrate phase equilibria in brines composed of mixed salts (NaCl, KCl, CaCl2 and MgCl2) for total salt concentration up to 29.2 wt% and for pressures ranging from 20 to 200 MPa (2900 to 29,000 psia). Data under these conditions are the first reported and they add significant value in furthering knowledge of the phase space for hydrate formation. In addition, these data are used for the development and assessment of models to capture hydrate phase equilibria over a wide range of salt concentrations and pressures. At last, critical factors (such as pressure, salt species, and concentration) that influence the hydrate suppression temperature relative to the uninhibited (salt-free) systems are also investigated.