The different roles of fluid conduits for marine gas hydrate systems: A global review

Abstract

ABSTRACT Fluid conduits play important roles in the dynamic evolution processes of marine gas hydrate systems (GHS), but detailed analysis of these specific roles has been inadequate. In this paper, various types of gas hydrate-related fluid conduits are analysed by examining abundant global case studies mainly using seismic data, and the interaction of these fluid conduits with the GHS is analysed. Results show that faults and gas chimneys are the most common fluid conduits, accounting for ~80% of the analysed GHS-related conduits. Other fluid conduits include permeable dipping strata, polygonal faults, mud/salt diapirs, mud volcanoes, and unconformity surfaces. Two groups of fluid conduits can be classified according to their roles for the GHS. Group 1 fluid conduits mainly exist underneath the GHS which transported deeper gas upwards to the GHS, providing gas source to form gas hydrates or the underlying free gas zone (FGZ). Group 2 fluid conduits are less in quantity compared to group 1, accounting for ~28% of the analysed conduits and often located at shallower depth within the GHS. When the FGZ is critically pressured due to the continuous accumulation of free gas or gas hydrates dissociate, group 2 fluid conduits may be triggered or reactivated, channelling free gas to the shallower layers or even the seabed. Group 1 fluid conduits mainly play a positive role in the formation of the GHS, while group 2 fluid conduits may play a role in affecting the seabed ecosystem or even climate change due to the gas escape to the seabed or even the sea water. Generally, this classification method can help better understand the roles of fluid conduits for the GHS, which should be widely applicable in other gas hydrate study areas.