This paper describes experiments on hydrate decomposition. Destabilizing reagents, such as methanol solutions or warm liquids, were injected into a pressurized cell containing synthesized methane hydrate or hydrate composites. A unique facility was employed to better simulate conditions that would prevail during in situ destabilization in hydrate-rich, deep ocean sediments. A one-dimensional model was developed to interpret the experimental results. The primary goal was to further elucidate methane hydrate dissociation kinetics under conditions relevant to practical gas extraction scenarios.
Gas hydrates are crystalline compounds which occur when water forms a cage-like structure around gas molecules such as methane. Hydrates are found both in permafrost and in deep ocean marine sediments under favorable thermodynamic conditions of low temperatures and high pressures. There is growing interest in gas hydrates because of their potential as a future energy resource and the possible threat they pose to seafloor stability and global climate (for a comprehensive review of the subject see, for example, Max, 2000). Because of their greater accessibility, shallow permafrost hydrate resources located in the Arctic have been the most actively targeted for resource assessment and pilot scale research and development projects (Sharma et al. 1992).
Several methods to extract gas from hydrates for energy have been proposed: depressurization, thermal stimulation, and inhibitor injection. These schemes are all based on the in-situ dissociation of hydrates into gas and water. In order to develop such methods safely and economically, it is necessary to understand the underlying physical phenomena as well as possible. Of particular importance are the kinetics of methane hydrate decomposition, since any practical exploitation of hydrate resources would depend on the basic time scales of the process. For given thermodynamic conditions, there exists a fundamental intrinsic rate of hydrate decomposition, a speed limit of sorts imposed by molecular constraints.
