Defining the updip extent of the gas hydrate stability zone on continental margins with low geothermal gradients

Abstract

The distribution of gas hydrate on a continental slope is often characterized as a wedge that pinches out on the seafloor. This part of the hydrate stability zone is particularly relevant for studies of the dynamics of hydrate accumulations, such as processes related to slope stability or hydrate dissociation leading to methane release into the overlying ocean. For regions with very low geothermal gradients, we have produced a series of thermobaric models of the shallow hydrate stability zone that contain an unexpected geometrical distribution of hydrated sediments. In these models, the shallowest part of the stability field thickens and bulges landward. Such a feature is more likely to happen in regions where low geothermal gradients are further lowered by high sedimentation rates. Also, the effect is greater beneath colder oceans. Although a hydrate stability zone bulge would be difficult to image with conventional seismic methods, there are numerous locations around the world where such a system could develop.