Slope instability of submarine sediments due to hydrate dissociation: A case study of Northern Cascadia Margin.
Document Type
Article
Publication Date
4-1-2023
Abstract
Gas hydrates constitute a significant portion of pore spaces in the continental shelves around the world. Major changes in the marine environments, including warming or depressurization may cause the hydrate stability to change and massive amount of methane gas to migrate up into the ocean water. One significant risk is the stability of these slopes, which have been mechanically strengthened by cementitious gas hydrates for thousands of years. In this study, coupled Thermo-Hydro-Mechanical (THM) simulations are performed to quantify the slope failure risks associated with dissociating hydrates. The widely investigated region of Northern Cascadia Margin is used as the model domain with two slopes facing opposite directions. Depressurization and ocean water warming scenarios are investigated to measure the depletion in hydrate reserve and slope movement caused by the resulting decline in geomechanical strength. Both the scenarios are capable of dissociating large amount of methane hydrates and causing rockslides along hydrate bearing zones. The risk associated with depressurization is higher as the effective stress is increased by a drop in pore pressure during methane production through hydrate-rich toes of the slopes. A short production scenario of 180 days yielded in higher displacement than warming of seafloor. The warming scenario based upon climate research for several years is tested for slope failure and the resulting mass movement of a few meters is not significant to cause alarm, assuming a steady 0.5–3 °C rise in temperature over 100 years. A third scenario with significantly depleted hydrate bearing sediment is subjected to a short duration of horizontal sinusoidal dynamic load representative of a major earthquake event may cause significant mass movement of up to tens of meters and is a cause for concern. This study aims to predict the nature of the geo-hazards associated with hydrate dissociation, due to slow global climate rise, depressurization event or short-term earthquakes that the region can experience.
Publication Source (Journal or Book title)
Geoenergy Science and Engineering
Recommended Citation
Dhakal, S., & Gupta, I. (2023). Slope instability of submarine sediments due to hydrate dissociation: A case study of Northern Cascadia Margin.. Geoenergy Science and Engineering, 223 https://doi.org/10.1016/j.geoen.2023.211558