Diverse gas composition controls the Moby-Dick gas hydrate system in the Gulf of Mexico

In marine basins, gas hydrate systems are usually identified by a bottom simulating reflection (BSR) that parallels the seafloor and coincides with the base of the gas hydrate stability zone (GHSZ). We present a newly discovered gas hydrate system, Moby-Dick, located in the Ship Basin in the norther...

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Bibliographic Details
Published in:Geology
Main Authors: Portnov, Alexey, Cook, A.E., Vadakkepuliyambatta, Sunil
Format: Article in Journal/Newspaper
Language:English
Published: Geological Society of America 2021
Subjects:
VDP::Mathematics and natural science: 400::Geosciences: 450
VDP::Matematikk og Naturvitenskap: 400::Geofag: 450
Arctic
Online Access:https://hdl.handle.net/10037/22219
https://doi.org/10.1130/G49310.1
Description
Summary:In marine basins, gas hydrate systems are usually identified by a bottom simulating reflection (BSR) that parallels the seafloor and coincides with the base of the gas hydrate stability zone (GHSZ). We present a newly discovered gas hydrate system, Moby-Dick, located in the Ship Basin in the northern Gulf of Mexico. In the seismic data, we observe a channel-levee complex with a consistent phase reversal and a BSR extending over an area of ∼14.2 km2 , strongly suggesting the presence of gas hydrate. In contrast to classical observations, the Moby-Dick BSR abnormally shoals 150 m toward the seafloor from west to east, which contradicts the northward-shallowing seafloor. We argue that the likely cause of the shoaling BSR is a gradually changing gas mix across the basin, with gas containing heavier hydrocarbons in the west transitioning to methane gas in the east. Our study indicates that such abnormal BSRs can be controlled by gradual changes in the gas mix influencing the shape of the GHSZ over kilometers on a basin scale.

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