Heterogeneity properties of methane hydrate formation in a pilot-scale hydrate simulator

Abstract

The accumulation and distribution features of gas hydrates are the significant issues affecting the hydrate resource assessment, the hydrate dissociation behaviors, and the risk evaluation of hydrate exploitation. This work aims to investigate the methane hydrate formation process by numerical simulation based on the experimental data in a pilot-scale hydrate simulator. Methane hydrate is formed by multi-step water injection method. Simulation results of the evolutions of the temperature, the system pressure, the mass of formed hydrate, and the remaining mass of methane gas are in good agreement with those of the experiment. The spatial distributions of the gas, water, and hydrate are all found to be very heterogeneous in the vessel during the whole simulation period. The free methane gas tends to accumulate in the pores near the upper boundary because of buoyancy and diffusion effects, while the liquid water shows an opposite trend under the gravity and capillary effects. Finally, the formed hydrates are found to be mainly accumulated in the upper area of the reactor due to the more favorable gas-water contact conditions, and the hydrate saturation decreases from the roof to the bottom layer by layer. In addition, the inhomogeneity of methane hydrate is more pronounced along the vertical direction than the horizontal one during the formation process. Generally, the heterogeneous formation of gas hydrate is dominated by the migration processes of gas and water in porous media. Moreover, the selected kinetic model is also important for the description of the heterogeneous hydrate formation behavior.