CO2 storage through clathrate hydrate formation

Subsurface CO2 sequestration and its permanent storage through clathrate hydrates formation is a novel method for reducing the concentration of carbon dioxide in the atmosphere. CO2 forms stable hydrate compounds at lower temperature and pressure conditions compared to other hydrate formers, especially CH4 hydrates (Figure 4). Since methane hydrates have been inferred to be present in permafrost and outer continental rises and slopes, and are known to have existed over many centuries, it should be possible to store atmospheric carbon dioxide as solid hydrate compounds in subsurface rock pores over many geological periods. This method is volumetrically efficient as each volume of hydrate can accommodate about 175 volumes of gas.

Figure 4. Phase diagram for simple CH4, CO2 and mixed CH4-CO2 hydrates.

Figure 4. Phase diagram for simple CH4, CO2 and mixed CH4-CO2 hydrates.

Low temperatures, high pressures and the availability of adequate amounts of hydrate-forming gas are the necessary conditions for hydrate formation that are known to be prevalent in natural permafrost sediments in oil and gas reservoir provinces. Drilling, exploration and production activities for the exploitation of these oil and gas reservoirs have been taking place over many decades. Carbon dioxide sequestration in the sedimentary sections, which have been depleted of oil and gas volumes, would not only re-pressurize these reservoirs and consequently produce oil and gas, but would also safely store the injected carbon dioxide as clathrate hydrates in the later stages. In-place infrastructure can be used to inject the carbon dioxide into subsurface permafrost sedimentary sections (including formations other than oil and gas provinces), which would diminish the cost of CO2 disposal. Injected CO2 would be converted into hydrates and occupy the pore spaces of the host rock. The possibility of their atmospheric seepage would be very little as the overlying permafrost layers would act as an impermeable barrier in the form of a cap rock, thus preventing diffusion or upward migration of CO2 through pores (Duxbury and Romanovsky, 2004; Clarke, 2001). Even in offshore sediments where oil and gas reservoirs exist, there is an increased chance of hydrate accumulations associated with them (e.g. North Sea, Indian Ocean, Taiwan).

Our experimental investigations were aimed at better understanding the processes affecting CO2 injection into CH4 hydrate reservoirs, thereby allowing permanent storage of CO2 in the form of clathrate hydrates.

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