The Effect of Molar Liquid Water-Gas Ratio on Methane Hydrate Formation

Abstract

Experimental results and analysis among different hydrate research groups are very often not transplantable, partly due to the intrinsic stochastic nature of hydrate formation, partly due to different experimental conditions, gas compositions and analyzing techniques used or applied. In the present work the effect of the molar liquid water-gas ratio (γm) on both nucleation and growth of methane hydrate has been examined. Structure I methane hydrates were formed under isochoric conditions in stirred cell during constant cooling, and the point of spontaneous nucleation (PSN) was recorded. The results show that change of γm gave no significant effect on average induction time, average nucleation rate or average sub-cooling at PSN. Nevertheless, nucleation behaved more stochastic when the volume fraction of water and γm increased. Moderate γm values that were closer to the theoretical hydration number (5.9 to 6 at the experimental conditions) could achieve larger total gas consumption and higher hydrate formation rate. Imbalanced γm values (either highly water-excess or highly gas-excess) may however lead to smoother behavior of crystal growth.