Timescales and Processes of Methane Hydrate Formation and Breakdown, With Application to Geologic Systems

• Published in: Journal of geophysical research. Solid earth Vol. 125; no. 8
• Main Authors: Ruppel, C. D., Waite, W. F.
• Format: Journal Article
• Language: English
• Published: 01.08.2020
• Subjects: gas hydrate; geologic systems; hydrate breakdown; hydrate formation; marine hydrate; permafrost hydrate
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2018JB016459

Gas hydrate is an ice‐like form of water and low molecular weight gas stable at temperatures of roughly −10°C to 25°C and pressures of ~3 to 30 MPa in geologic systems. Natural gas hydrates sequester an estimated one sixth of Earth's methane and are found primarily in deepwater marine sediments on continental margins, but also in permafrost areas and under continental ice sheets. When gas hydrate is removed from its stability field, its breakdown has implications for the global carbon cycle, ocean chemistry, marine geohazards, and interactions between the geosphere and the ocean‐atmosphere system. Gas hydrate breakdown can also be artificially driven as a component of studies assessing the resource potential of these deposits. Furthermore, geologic processes and perturbations to the ocean‐atmosphere system (e.g., warming temperatures) can cause not only dissociation, but also more widespread dissolution of hydrate or even formation of new hydrate in reservoirs. Linkages between gas hydrate and disparate aspects of Earth's near‐surface physical, chemical, and biological systems render an assessment of the rates and processes affecting the persistence of gas hydrate an appropriate Centennial Grand Challenge. This paper reviews the thermodynamic controls on methane hydrate stability and then describes the relative importance of kinetic, mass transfer, and heat transfer processes in the formation and breakdown (dissociation and dissolution) of gas hydrate. Results from numerical modeling, laboratory, and some field studies are used to summarize the rates of hydrate formation and breakdown, followed by an extensive treatment of hydrate dynamics in marine and cryospheric gas hydrate systems. Key Points Gas hydrates are widespread, store large amounts of carbon, and are susceptible to degradation under warming ocean‐atmosphere conditions Gas hydrate formation and breakdown rates are generally limited by mass transport and heat transport processes, respectively Hydrate dissolution, not dissociation, is the more common breakdown process; sufficient dissolved gas in adjacent fluids is necessary for hydrate to persist