Fundamental Studies of CO2 Substitution in Methane Hydrate
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Fundamental Studies of CO2 Substitution in Methane Hydrate

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The enormous energy reserve of methane gas stored in gas hydrate structures is substantially more than all known fossil fuel reserves around the world. Efficient extraction of methane from the hydrate cavity structures is still a technological challenge but the use of CO2 injection and substitution is a potentially viable approach. Gas hydrates in sediments are in a state of stationary balance with their surroundings. They are not in thermodynamic equilibrium and competing phase transitions of hydrate dissociation and hydrate reformation determines the stationary situation. The specific objective of this research is to dictate the phase transition conditions that enhance the growth rate of CO2 hydrate and increase the dissociation rate of methane hydrate in porous media by understanding the behavior of surfactants in promoting the growth rate of CO2 hydrate experimentally. In addition, the investigation explores the addition of a small amount of nitrogen gas to increase permeability following dissociation of CH4 hydrate. The CO2-CH4 gas exchange concept is theoretically more efficient than any other methods for extracting methane from gas hydrate reservoirs but the theory has not previously been demonstrated experimentally. Furthermore, due to increased concerns regarding carbon dioxide emissions as a driver of global warming, CO2 hydrate formation may be a promising form of CO2 storage as well as an efficient strategy for CH4 recovery. New CO2 hydrate forms from injected CO2 and free liquid water in the porous media. When the CO2 hydrate forms, the released heat from this formation is directed through the water phase and causes CH4 hydrate to dissociate. The experimental results illustrate that 20 moles% N2 and 1 mole% NFM (N-formylmorpholine) with CO2 liquid injection is the most effective of the conditions tested for conversion between CO2/CH4 hydrates. Maximum conversion in this study was 88 moles% of CO2, and 2 moles% N2 taking the place of methane hydrate in large and small cavities. This research work also uses theoretical modeling to evaluate efficient production schemes in order to develop a feasible method for future practical implementation. It is known that a critical element in the dynamics of hydrate phase transitions is the mass transport, as the hydrate forms across a thin interface layer between liquid water and the interacting gas phase. An efficient production scheme needs to be able to break the water hydrogen bonds in this interface. On the other hand, the kinetic rate of hydrate growth also depends strongly on hydrate formation at the interface. This study shows how the balance of film barrier and hydrate growth at the interface can be affected by a judicious selection of surfactants.

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