OS1C-2：HYDRATE-BEARING CLAYS: A SLOPE STABILITY ISSUE?

Jeffrey PRIEST & Jocelyn LH GROZIC
Department of Civil Engineering, University of Calgary, CANADA

　　Recent marine gas hydrate expeditions have made use of advances in pressure coring and imaging technology to reveal that gas hydrates readily form in clay-rich sediments. In these environments, the hydrate exhibits a complex structure and form, evidenced as fracture-filled near-vertical veins displacing the sediment. These hydrate veins contribute to enhanced sediment strength; strength that may result in under-compaction of the sediment as the reinforcing hydrate-veins help support the overburden pressure during ensuing sedimentation. Should perturbations to the thermodynamic system occur and hydrate dissociation be induced, dramatic changes in sediment strength may occur.

　　During hydrate dissociation a number of factors can arise that may influence the behavior of the sediment, such as changes in pore water salinity, loss of structural strength of hydrate veins, increase in pore pressure, hydrate saturation, etc. The role of each of these factors on sediment strength is not clearly understood, and therefore the relationship between hydrate dissociation and slope instability, particularly for hydrate-bearing, clay-dominated, marine sediments is not well understood. In this paper we help provide some insight into the importance of each of these factors on sediment behavior through reference to existing data from the literature, and the results from laboratory tests carried out by the authors. We then explore, qualitatively, the potential relationship between hydrate dissociation, sediment strength and slope instability for clay-rich hydrate bearing marine sediments.

　　In Arctic regions, hydrate is extensively distributed within the clay-dominated continental shelf sediments, and due to cold waters in these regions, hydrate forms at shallower depths than elsewhere. Given the observed amplification of climate change in Arctic regions, these particular hydrate-bearing sediments may be relatively more sensitive to disturbance and potential instabilities. The improved understanding of the relationship between hydrate dissociation and sediment strength will therefore help us develop quantitative models, both physical and numerical, to more accurately assess the impact of such changes on Arctic marine sediments.