Our work on gas hydrates is broadly focused on understanding how hydrates form and accumulate in marine sediments and how host sediment properties interact with hydrates during pressure and temperature perturbations on geological and production timescales. Current we have 3 hydrate-related projects.
Forecasting marine sediment properties on and near the Arctic shelf with geospatial machine learning
Collaboration with Sandia National Laboratories – PI Jennifer Frederick
In this project, we are using machine learning approaches to predict the properties of seafloor sediments in the Arctic and how those properties propagate downward during burial and affect hydrate and gas distribution. We are interested in how Arctic marine hydrates will respond to ocean warming.
In an example calculation based on sediment properties at Ocean Drilling Program (ODP) Site 908 (Fig. 1), pore-size effects initially place the base of hydrate stability at 351 mbsf (Fig. 2, left). After a temperature increase of 3°C, the base of hydrate stability moves up to 294 mbsf (Fig. 2, right), causing hydrate in 57 m of sediments to dissociate into gas. This gas column could have a significant effect on sediment strength.
Figure 1. Location of ODP Site 908.
Figure 2. Initial phase equilibrium conditions (left), and after a temperature increase of 3°C (right) at Site 908. The base of the hydrate stability zone is indicated with green lines, and the thickness of dissociated hydrate is indicated by the blue box.
Tectonic stress effects on methane seepage (SEAMSTRESS)
Collaboration with Center for Arctic Gas in the Environment (CAGE), University of Tromsø – PI Andreia Plaza-Faverola
This project is focused on understanding the relationship between far-field tectonic stresses, state of stress in the sediment column, and gas venting on Vestnesa Ridge offshore Svalbard (Fig. 3). We are using sediment cores, downhole pressure measurements, and numerical models to determine overpressures and fluid fluxes to better understand where tensile fractures may be occurring.
Figure 3. Top: location of Vestnesa Ridge with relevant tectonic features. STF = Spitsbergen transform fault; MR = Molloy Ridge; MTF = Molloy transform fault; KR = Knipovich Ridge; VR = Vestnesa Ridge. Bottom: shallow seismic section with bathymetry showing location of active and inactive gas vents on Vestnesa Ridge. BSR = bottom-simulating reflection; GHSZ = gas hydrate stability zone. Figures modified from Plaza-Faverola et al. (2017).
Methane migration and hydrate accumulation in the Gulf of Mexico
Through several projects funded by the U.S. Department of Energy and industry partners, we have been investigating how coarse-grained reservoir units in the Gulf of Mexico fill with hydrate and the migration mechanisms that supply the necessary methane (Fig. 4). This work has included a combination of numerical simulation and laboratory experiments. Our results have shown that locally generated microbial methane is the source of many hydrate deposits, but that complex processes are necessary to deliver that methane to appropriate reservoirs. These processes include recycling as hydrate-bearing sediments are buried beneath the base of the hydrate stability zone, transport along faults, and smaller-scale processes like convection driven by salinity contrasts within individual sand layers.
Figure 4. Methane migration mechanisms in Gulf of Mexico sediments. Brown represents mud; yellow represents sands. A: Short-distance diffusion or advection of microbial methane. B: Advection of dissolved methane. C: Advection of a gas phase.
Plaza-Faverola, A., Vadakkepuliyambatta, S., Hong, W.-L., Mienert, J., Bünz, S., Chang, S., Greinert, J., 2017. Bottom-simulating reflector dynamics at Arctic thermogenic gas provinces: An example from Vestnesa Ridge, offshore west Svalbard. Journal of Geophysical Research Solid Earth, 122(6), 4089-4105, https://doi.org/10.1002/2016JB013761.