RECOVERY OF GAS FROM METHANE HYDRATE RESERVOIR BY SIMULTANEOUS DEPRESSURIZATION AND N2 INJECTION
Recovery of natural gas hydrates has been a matter of accrued interest to the researchers all over the world. Depressurization is known to be an advantageous technique over thermal stimulation and inhibitor injection methods for decomposing the hydrate reservoirs. This work takes the case of methane recovery by pure depressurization and compares it with the technique of depressurization that is aided with N2 injection. In assumed thermodynamic scenario, injection of N2 does not results into hydrate formation neither it is liquefied. A one dimensional (1D) model of an underground class 3 hydrate reservoir with production and injection well at its two ends is assumed to contain free CH4 gas, methane hydrate and water initially. Constant pressure injection and depressurization is carried out at the two distinct wells. Model includes transient non-isothermal multiphase multi component transport through porous media wherein gas and aqueous phases are mobile while hydrate phase is immobile. Mass, momentum and energy conservations are enforced to form the governing equations. Discretization of governing equations is achieved using finite difference method and equations are solved sequentially with several iterations within one-time step. Results of simulation run for N2 injection assisted depressurization technique shows an improvement in the methane gas production rate over that due to pure depressurization.