Review articleNatural gas hydrates occupying fractures: A focus on non-vent sites on the Indian continental margin and the northern Gulf of Mexico

•We review gas hydrate filled fracture occurrence at sites without vents or chimneys.•We find resistivity is the only physical property always affected.•Fractures usually are near-vertical and are similarly oriented at the same site.•Fractures do not intersect the base of the gas hydrate stability zone.

We present a review of the geophysical and petrophysical properties of gas hydrate-filled fracture sites that are not associated with a gas vent or chimney from the Indian National Gas Hydrate Program Expedition 01 and the Gulf of Mexico Gas Hydrate Joint Industry Project Legs I & II. We analyzed logging-while drilling (LWD) resistivity images, well logs and coring information at eight of these sites and found in all cases that the gas hydrate-filled fractures occurred in fine-grained sediments, were near-vertical, and were generally oriented in the same direction at each site. In addition, resistivity was the only physical property always affected by presence of near-vertical gas hydrate-filled fractures, though in one case only the LWD resistivity image detected the presence of gas hydrate. Gas hydrate-filled fractures did not intersect the base of the gas hydrate stability zone at the location of the wellbore at any of the sites. We suggest that at non-vent/non-chimney sites the methane occupying the gas hydrate is likely produced microbially in situ and is not sourced from below.