Effect of KCl and MgCl2 on the kinetics of methane hydrate formation and dissociation in sandy sediments

Abstract

Natural gas hydrate is one of the potential energy resources in the future. However, the extraction of energy from hydrates remains uncertain due to limited understanding on how hydrates are formed and dissociated under different perturbations. More than 90% of NGH resource exists within marine location where salts are present. In this study, we investigated the formation and dissociation behavior of methane hydrate in the presence of magnesium chloride (MgCl2) and potassium chloride (KCl), two salts found in seawater, at 1.5 wt% and 3.0 wt%; and compared it with the cases of water and NaCl from our previous work. We found that on top of thermodynamic inhibition, both MgCl2 and KCl act as kinetic inhibitors on hydrate formation, retarding the rate of formation – with KCl exhibiting a weaker inhibition compared to MgCl2. For hydrate dissociation via thermal stimulation, we demonstrated that hydrate dissociates more rapidly in the presence of salts as compared to water despite a comparable temperature driving force (ΔT = 5.3 K) applied. Our results indicated that the weaker thermodynamic inhibitor, KCl, has a milder kinetic inhibition effect on hydrate formation and a weaker promoting effect on hydrate dissociation as compared to MgCl2 and NaCl.