The overarching goal of this project is to find a viable method for using carbon dioxide to produce the vast resources of natural gas locked up as solid gas hydrates in permafrost and oceanic margin zones.
The natural gas hydrates are converted to CO2 hydrates, thereby storing CO2 (the major greenhouse gas) while simultaneously releasing natural gas. This so-called “swapping” process, whereby methane (the major component in natural gas) in the hydrate is replaced by CO2, allows for production of natural gas from hydrate without adversely affecting the stability of the solid hydrate.
The main objective of this PhD project is to understand the mechanism of the swapping process with the goal of achieving highly efficient production of methane gas and CO2 capture simultaneously. Based on experimental data, the mechanism of swapping process will be simulated. The stability of the newly formed hydrate after swapping will also be studied.
Gas hydrates, a type of ice-like clathrate compounds, can be decomposed if the temperature and pressure are outside their hydrate stability zone, or the chemical equilibrium between the hydrate phase and the adjacent environment is disturbed.
An abundance of methane (CH4) is trapped in gas hydrates together with other small amounts of hydrocarbons or other gases in subsea sediments and permafrost regions.
Several methods have been suggested for methane recovery from gas hydrates, such as depressurization, thermal stimulation, inhibitor injection, and carbon dioxide (CO2) replacement, or combinations of the above.
The CO2 replacement method is based on the fact that the chemical potential of the CH4 hydrate is higher than that of the CO2 hydrate. Theoretically, CO2 molecules have a relatively high tendency to replace the methane molecules from the methane hydrate cages.
Under ideal conditions, such as high specific surface areas, high permeability, good heat and mass transfer in the process of CO2 replacement, the process could be fast and efficient. However, the replacement rate is a bottleneck in the process of swapping since the CO2 hydrate cell coats the surface of the natural gas hydrate.
Depressurization reduces the reservoir pressure beyond the hydrate stability zone to initiate hydrate dissociation. Depressurization is a feasible and less energy consuming method which has been successfully applied to produce methane gas. A combination of the replacement process and depressurization is thus proposed in this project.