The project goal is to create models that will be used to improve forecasts of slope stability and pockmark development, which could prevent disruptions of hydrate reserves and possible release of hydrates into the atmosphere.

University of Oregon, Eugene, OR 97403-5219

Natural gas hydrate reservoirs are dynamic systems that evolve gradually but can also decompose abruptly resulting in submarine slope failure and pockmark formation. Both the accelerated exploitation of unconventional hydrocarbon reserves and environmental changes can increase the potential for enhanced hydrate dissociation that could lead to methane release. Model simulations are capable of approximating bulk reservoir characteristics, but these efforts must be complemented and enhanced by more finely resolved treatments that account for underlying microscale effects. Emerging developments in our knowledge of deposit variability can lead to further advances in mechanical models of slope stability that have been restricted to describing interactions with laterally homogeneous or slowly varying hydrate reservoirs and rate-independent friction. More sophisticated and physically realistic models updated with information about slip instabilities along tectonic faults can be extended to include the dynamic feedback resulting from fluid pressurization, dilatancy, and phase changes. Studying essential physical interactions over a broad range of time- and length-scales can help researchers predict the potential of hydrate reservoirs to transform into geohazards that could threaten commercial infrastructure and damage environmental systems.

Methane hydrates in arctic and deep-water deposits are crucial components of potential future energy supplies and a potent store of greenhouse gases. As hydrates evolve in response to ongoing environmental shifts, researchers must evaluate the potential for hydrate resources to be transformed into geohazards. This project will markedly advance our understanding of how hydrate anomalies develop and the potential for environmental forcing to cause them to dissociate and disrupt sedimentary structures. The project models will improve forecasts of slope failure and the development of gas-escape features that would diminish hydrocarbon reserves, release greenhouse gasses, and pose threats to energy infrastructure.

• The researchers have developed a model that determines the time over which a given magnitude of consolidation must occur to cause a slope to become unstable. They have also developed a model for determining the influence of rate and state dependent friction and elastic stress transmission on slope stability. By performing an elastic analysis, they can examine how stress is transmitted by the accumulation of strain between regions that undergo different amounts of slip. When the size of the slipping patch is small, stress transmission to nearby stable regions prevents catastrophic failure even after the local factor of safety is reduced below unity. When the patch exceeds a critical nucleation size, however, a landslide is expected to result. They have also completed an analysis of the infinite-slope stability problem for comparison, and verified that results are consistent with published analyses.
• Researchers have used the conservation laws to derive governing equations that describe water, methane, salt, and heat flow. They have developed a working two-phase model for the coupled evolution of dissolved gas, heat, salt, and hydrate in submarine sediments in response to a specified advective supply through the lower boundary and have extended this model to include a dynamic three-phase stability boundary and treat the evolution of free gas concentration below. They have found that, on their own, salinity anomalies are unlikely to be sufficiently pronounced to enable the three-phase zones to propagate significant distances. Their effects can be magnified in combination with the influence of focused advection of heat from below.
• Researchers have developed a code that can assemble a distribution of spherical particles into a model porous medium with a distribution of pore characteristics. Monte Carlo integration techniques were then utilized to predict the methane solubility as the hydrate saturation level changes. These model predictions have been tested against published empirical data for the related problem of ice formation in mono-dispersed porous media.
• Researchers have developed a one-dimensional consolidation code that predicts changes in porosity with changes in effective stress.
• Researchers have developed idealized models for the accumulation of hydrates and the evolution of salt, temperature, and free gas content near boundaries in bulk sediment characteristics inclined at specified angles to the background porous flow.
• Researchers have used models to predict the effects of sediment properties on gas solubility in order to compare predicted hydrate accumulation with published observations of hydrate distributions near stratigraphic boundaries.

(December 2015)
Researchers are using rate-and-state friction models to examine how slope stability is affected by the dissolution of hydrate from finite anomalous zones and are examining conditions under which saline regions can develop and enable three-phase equilibrium near stratigraphic boundaries where hydrate anomalies develop.

$276,804

$71,740

NETL – Adam Tew(Adam.Tew@netl.doe.gov or 412-386-5389)
University of Oregon – Dr. Alan Rempel (rempel@uoregon.edu or 541-346-6316)