The research on the natural gas hydrate dissociation kinetic from hydrate-sediments/seawater slurries

Abstract

Due to the weak cementation of natural gas hydrate (NGH) reservoir in the seabed, during both the drilling and development processes, a multiphase (gas hydrate-sediments-seawater-natural gas mixture) flow is more likely to exist in the NGH reservoir and development wells, understand the natural gas hydrate particle dissociation kinetic in the hydrate-sediments/seawater slurries is important. In this work, first, a new NGH phase behavior research experimental apparatus contains a strong magnetic stirrer was built. By using this, we for the first time proposed to form NGH reservoir in the water saturated sands under stirring in the laboratory, which showed a much higher hydrate formation rate and water to hydrate conversation ratio than the usual static formation method. After that, the CH4 hydrate-sands/seawater slurries were produced, the influence of pressures, temperatures, the size of sands, and stirring rates on CH4 hydrate dissociation kinetic in the slurry were investigated. The dissociation rate of CH4 hydrate-sands mixed particles markedly increased with decreasing operation pressure from 3 MPa to 0.1 MPa. The average dissociate rate reached 1762.57 mL/min at 0.1 MPa. It is interesting that unlike to the single NGH reservoir, no hydrate secondary formation and ice formation phenomenon arose in the hydrate-sands/seawater slurries during the CH4 hydrate dissociation process. The increase of temperature and stirring rate substantially stimulated the dissociation of CH4 hydrate particles in the slurry, while the sands’ size showed little effect. In addition, a high precision kinetic model for describing the dissociation of CH4 hydrate in hydrate-sands/seawater slurries was built, in which the influence of pressure, temperature and stirring rate on the hydrate apparent dissociation rate constant was considered at the same time.