Volume 26: Closing Carbon Cycles – A Transformation Process Involving Technology, Economy, and Society: Part I

Effect of ions on Methane Hydrate Phase Equilibrium in Deep-Water Environment of “Haima” Cold Seep Yanyan Huang, Jingchun Feng , Yan Xie, Zhenwu Zhou, Junwen Wang, Pian Li, Mingrui Zhang, Liwei Sun

Abstract

The mechanism researches on seabed methane fate are a critical part to reveal the global methane budget. Hydrate formation by natural gas bubbles in the course of seepage is an essential way for methane capture and fixation. Nevertheless, the hydrate phase equilibrium characteristics that affect the stability of hydrate formation during the bubble ebullition process are unclear. “Haima” cold seep is a typical active methane seeping environment associated with abundant methane hydrate, which necessitates unveiling the stability of methane hydrate formation. This work investigated the hydrate phase equilibrium conditions based on the in-situ water depth and practical ion categories and salinity. The results show that the strength of inhibition of methane hydrate in chloride salts of 3.45wt% salinity was in the order of Mg2+ > Na+ > Ca2+ > K+, Mg2+ > Ca2+ > Mn2+ > Ba2+. The mechanism of different ions categories effect on hydrate equilibria can be elucidated by the difference of charge and radius of the ions. Hydrate phase transition enthalpies was calculated by the Clausius-Clapeyron equation. The response law of hydrate phase transition enthalpy was almost consistent with the phase equilibrium change. This work have important reference value for the mechanism exploration about how hydrate formation characteristic is influenced by ions in “Haima” cold seep environment.

Keywords gas hydrate, phase equilibrium, seawater ions, cold seep