Analytical Investigation of Gas and Water Production from Aqueous-Rich Hydrate-Bearing Sediments by Depressurization

There have been several field production tests carried out from marine natural gas hydrate reservoirs, suggesting hydrates as a promising alternative energy source. However, the production performance is lower than expected with low productivity. Marine natural gas hydrate deposits are mostly water-saturated; the natural gas recovery process would be hindered by water production. In this work, gas hydrate dissociation was conducted in a water-saturated reservoir with three kinds of porous media under different production pressures. A lower production pressure can increase gas production but results in high water production, leading to a low gas-water ratio and low production efficiency. A low porous media permeability can significantly reduce water production. The Stefan (Ste) number and average gas production rate are employed to evaluate the sensible heat effect of the reservoir. There is a positive correlation between the Ste number and the average gas production rate; a large Ste number indicates a more sufficient heat supply for hydrate dissociation, resulting in a high gas production rate. The influence of the production pressures and sediment properties on the gas/water production performance from water-saturated hydrate-bearing sediments are demonstrated, and further insight is provided to optimize production techniques for field tests.