Methane Hydrates: Mechanical Properties and Recovery Issues

Nowadays, methane hydrates are viewed as a potential energy source but their exploitation is challenging for many technical and environmental reasons. The thermodynamic conditions that govern the formation, stability, and dissociation of gas hydrates, mostly methane and carbon dioxide hydrates, their structure, mechanical, thermal, and flow properties are addressed in a fluid-saturated porous media context and brought in a computational format. Standard and prospective production methods are reviewed. Gas hydrates are solid crystalline compounds, looking like ice, formed by natural gas components, e.g. methane, ethane, hydrogen sulfide, carbon dioxide, which occupy lattice positions in the water structure. The gas is not chemically bound to water. Hydrates contribute to a large part to the mechanical properties of the hydrate-bearing sediments. Therefore, their dissociation by depressurization, thermal or chemical methods, leaves a weakened mechanical resistance that may trigger underwater slope slides over large areas. Attempts to replace methane by carbon dioxide briefly reviewed, a process that at once would enhance methane production, maintain the mechanical properties of the hydrates, and sequestrate a greenhouse gas.