The use of electrical heating for the enhancement of gas recovery from methane hydrate in porous media

The gas production behaviors of methane hydrate dissociation induced by depressurization and electrical heating are investigated in a Cuboid Pressure Vessel (CPV) with an effective volume of 1.5 L. The vertical well located at the axis of the vessel is used as the production well, and a resistance heating wire is distributed uniformly in the inner surface of the well for heat injection. Hydrate samples with the similar phase saturations are prepared and then decomposed under depressurization and electrical heating. A total of five experimental runs have been carried out with different production pressure (3.50, 4.50, and 5.50 MPa) and electrical heating power (0, 25, and 50 W). It is found that methane hydrate can be dissociated continuously in the CPV in each run, which proves the feasibility of the used method for hydrate exploitation in porous media. Compared with the pure depressurization case (run 3), both the gas production and hydrate dissociation rates could be increased to a much higher level when a relatively slow heat injection rate is supplied from the well. In addition, the net energy Enet can be recovered with a much faster rate under constant electrical heating rate, and the final amount of Enet is only a little lower than that of run 3. They all indicate that the production efficiency of depressurization can be greatly enhanced by employing the electrical heating simultaneously. A maximum Enet can be obtained in each case with constant electrical heating, and it is suggested that the production process should be terminated before Enet begins to drop. The gas production performance is generally more favorable under lower production pressure and a higher electrical heating rate.