Applied Energy, Vol.229, 637-647, 2018
Effect of vertical wellbore incorporation on energy recovery from aqueous rich hydrate sediments
Natural gas hydrates, an abundant source of natural gas in nature, have the potential of supplying energy for the future. However, due to the complexity of physical processes that occur simultaneously during the dissociation of hydrates within porous media, further understanding on the dynamic behavior of hydrates dissociation (e.g. heat transfer associated with phase transition, permeability changes, and simultaneous gas/water production) is required to elucidate the process of gas recovery from hydrates. In this work, we investigate the effect of a single vertical wellbore incorporation on the production behavior from hydrates formed in sandy sediments (0.1-0.5 mm). Depressurization approach (3.5, 4.0 and 4.5 MPa) was applied to dissociate the hydrate-bearing sand at a constant surrounding temperature of 281.5 K. Through the incorporation of a vertical wellbore, the gas production rate decreased with increasing bottom hole pressure, and continuous production of gas was observed at 4.5 MPa even after 10 h of dissociation. For water production, a majority of water was produced within the first 2 h, beyond which only a small amount of water was recovered. It was also observed that the incorporation of a vertical wellbore in the current design and apparatus impeded hydrate dissociation, which was attributed to a stronger flow resistance for fluids to exit through the vertical wellbore. Cumulatively, the incorporation of vertical wellbore enhanced gas production by up to 8% and reduced water production by up to 42%. In the future, innovative production schemes, such as heated wellbore and hydraulic fracturing can be applied to further optimize gas production from hydrate-bearing sediments.