An Experimental Investigation on the Kinetics of Integrated Methane Recovery and CO2 Sequestration by Injection of Flue Gas into Permafrost Methane Hydrate Reservoirs.

Large hydrate reservoirs in the Arctic regions could provide great potentials for recovery of methane and geological storage of CO2. In this study, injection of flue gas into permafrost gas hydrates reservoirs has been studied in order to evaluate its use in energy recovery and CO2 sequestration based on the premise that it could significantly lower costs relative to other technologies available today. We have carried out a series of real-time scale experiments under realistic conditions at temperatures between 261.2 and 284.2 K and at optimum pressures defined in our previous work, in order to characterize the kinetics of the process and evaluate efficiency. Results show that the kinetics of methane release from methane hydrate and CO2 extracted from flue gas strongly depend on hydrate reservoir temperatures. The experiment at 261.2 K yielded a capture of 81.9% CO2 present in the injected flue gas, and an increase in the CH4 concentration in the gas phase up to 60.7 mol%, 93.3 mol%, and 98.2 mol% at optimum pressures, after depressurizing the system to dissociate CH4 hydrate and after depressurizing the system to CO2 hydrate dissociation point, respectively. This is significantly better than the maximum efficiency reported in the literature for both CO2 sequestration and methane recovery using flue gas injection, demonstrating the economic feasibility of direct injection flue gas into hydrate reservoirs in permafrost for methane recovery and geological capture and storage of CO2. Finally, the thermal stability of stored CO2 was investigated by heating the system and it is concluded that presence of N2 in the injection gas provides another safety factor for the stored CO2 in case of temperature change.

CO2 Capture by Injection of Flue Gas or CO2-N2 Mixtures into Hydrate Reservoirs: Dependence of CO2 Capture Efficiency on Gas Hydrate Reservoir Conditions.

Injection of flue gas or CO2-N2 mixtures into gas hydrate reservoirs has been considered as a promising option for geological storage of CO2. However, the thermodynamic process in which the CO2 present in flue gas or a CO2-N2 mixture is captured as hydrate has not been well understood. In this work, a series of experiments were conducted to investigate the dependence of CO2 capture efficiency on reservoir conditions. The CO2 capture efficiency was investigated at different injection pressures from 2.6 to 23.8 MPa and hydrate reservoir temperatures from 273.2 to 283.2 K in the presence of two different saturations of methane hydrate. The results showed that more than 60% of the CO2 in the flue gas was captured and stored as CO2 hydrate or CO2-mixed hydrates, while methane-rich gas was produced. The efficiency of CO2 capture depends on the reservoir conditions including temperature, pressure, and hydrate saturation. For a certain reservoir temperature, there is an optimum reservoir pressure at which the maximum amount of CO2 can be captured from the injected flue gas or CO2-N2 mixtures. This finding suggests that it is essential to control the injection pressure to enhance CO2 capture efficiency by flue gas or CO2-N2 mixtures injection.