Hydrate-bearing sediments
About 10,000 billion tons of mobile carbon constantly cycle through the solid Earth, ocean, and the atmosphere. Of this carbon, up to 20% is trapped in gas hydrate, an ice-like substance composed of methane and water. This dynamic carbon reservoir is envisioned as a potential energy resource, potential source of geohazards, and a potential driver for climate change. My work aims to evaluate these potentials by accurately describing the geomechanical and petrophysical behavior of this material. I rely on pressure cores¹, a technology whereby hydrates are preserved at high pressure and low temperature from sampling to testing.
Viscoplastic behavior of hydrate-bearing sediments
The geomechanical behavior of hydrate-bearing sediments controls gas production, wellbore design and seafloor stability. Using pressure cores² and hydrate-free material³, we have found that hydrates are viscoplastic materials: deformation, stresses and strength are rate-dependent. For example, during one-dimensional compression, we show that the stress state in hydrates is isotropic. Insights from our experimental observations are used to formulate a model, where the hydrate phase and sediment skeleton share any external load that is applied.
Permeability of hydrate reservoirs⁴
The water effective permeability controls the rate of pressure depletion during gas production and the ability to store CO₂ hydrate in the subsurface. Yet, a paradox is that laboratory-derived effective permeabilities of natural sediments are hundreds of times greater than those measured on synthetic samples, field observations, or theory suggests. We show that the use of methane-free water during storage and flow measurements dissolves the hydrate and results in flow channeling.
Selected publications
¹You K., Thomas C., Savage A., Cardona A., Flemings P.B., Murphy Z., and O’Connell J. (2024). Dissolved Methane Diffusion Drives Hydrate-Bearing Pressure Core Degradation During Long-Term Storage in Water, Energy & Fuels. doi:10.1021/acs.energyfuels.4c01487
²Cardona A., Bhandari A., and Heidari M. and Flemings P.B. (2023). The viscoplastic behavior of natural hydrate bearing sediments under uniaxial strain compression (K0 loading), Journal of Geophysical Research: Solid Earth, doi:10.1029/2023JB026976.
³Bhandari A., Cardona A. and Flemings P.B. (2023). The geomechanical response of the Gulf of Mexico Green Canyon 955 reservoir to gas hydrate dissociation: A model based on sediment properties with and without gas hydrate, Marine and Petroleum Geology, doi:10.1016/j.marpetgeo.2024.107000.
⁴Cardona A., Fang, Y., You K. and Flemings P.B., The effective permeability of hydrate reservoirs, Proceedings of the National Academy of Sciences (under review)
Offshore Hydrates: UT-GOM2 Expedition
A critical part of my hydrates research is the analysis and collection of field data. I have been part of the UT-GOM2 project — a U.S DOE-sponsored effort to locate, drill, and sample methane hydrate deposits from the deepwater Gulf of Mexico.
Recently, our team spent 34 days at sea and drilled two boreholes in over ~2 km of water to collect ~163 m of conventional and ~55 m of pressure cores. This is a multidisciplinary effort involving geosciences, engineering, microbiology and geochemistry.
More info can be found in the news and our expedition reports.