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 reservoirs

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.

Cardona 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.