Influence of the Particle Size of Sandy Sediments on Heat and Mass Transfer Characteristics during Methane Hydrate Dissociation by Thermal Stimulation

Abstract

Natural gas hydrate could be regarded as an alternative energy source in the future. Therefore, the investigation of the gas production from hydrate reservoirs is attracting extensive attention. In this work, a novel set-up was built to investigate sand production and sediment deformation during hydrate dissociation by heat stimulation. The influence of the particle sizes on the hydrate dissociation and sediment deformation was first investigated experimentally. The experimental results indicated that the rate of hydrate decomposition by heat stimulation was in proportion to the particle size of the sediment. The heat transfer rate and the energy efficiency decreased with the decrease of the particle size of the sediment. This was because higher permeability might lead to a larger sweep area of the fluid flow, which was beneficial for the supply of heat for hydrate dissociation. The sand production was found during hydrate dissociation by heat stimulation. The particle migration was due to the hydrodynamics of the water injection. The sand sediment expanded under the drive force from water injection and hydrate dissociation. Additionally, the smaller permeability led to the larger pressure difference leading to the larger sediment deformation. Because the sediment became loose after hydrate dissociation, small particle migration due to the hydrodynamics of the water injection could happen during the experiments. However, the sand production in the sediment with the larger particle size was more difficult, because the larger particles were harder to move due to the hydrodynamics, and the larger particles were harder to move across the holes on the production well with a diameter of 1 mm. Therefore, the sediment deformation during hydrate dissociation by heat stimulation should not be ignored.