Velocity mapping of steady water flow through methane hydrate bearing samples

The productivity of methane from natural gas hydrate reservoirs is predominantly controlled by the fluid migration mechanisms in hydrate-bearing sediments. Thus, the characterization of the effects of hydrate distribution on fluid migration is significant in the exploitation of natural gas hydrates. In this work, a phase contrast method was used to visualize water flow velocity fields at three cross-sections under different injecting flow rates by using magnetic resonance imaging (MRI). Four experimental cases were performed to directly measure the cross-sectional velocity fields in a sand packed hydrate-bearing sample with hydrate saturations varying from 22.5% to 32.7%. The effect of hydrate distribution on the water velocity fields was discussed. It was found that hydrate formed nonuniformly in the sand packed sample in all four cases, and the hydrate distribution predominantly affected the water effective permeability and cross-sectional velocity fields when steady water flow was injected. When hydrate saturation was higher than 22.5%, a two-region flow pattern was observed with a clear boundary between the fast-flowing region and the slow-flowing region. The cross-sectional flow rates calculated according to the velocity field images fitted well with the injecting flow rates.