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Diverse gas composition controls the Moby-Dick gas hydrate system in the Gulf of Mexico
Geology ( IF 5.8 ) Pub Date : 2021-12-01 , DOI: 10.1130/g49310.1
Alexey Portnov 1 , A.E. Cook 2 , S. Vadakkepuliyambatta 3
Affiliation  

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.

中文翻译:

不同的气体成分控制着墨西哥湾的 Moby-Dick 天然气水合物系统

在海洋盆地中,天然气水合物系统通常通过与海底平行并与天然气水合物稳定带 (GHSZ) 底部重合的底部模拟反射 (BSR) 来识别。我们展示了一个新发现的天然气水合物系统 Moby-Dick,它位于墨西哥湾北部的 Ship Basin。在地震数据中,我们观察到一个具有一致相位反转和 BSR 延伸到约 14.2 平方公里区域的河道堤岸复合体,强烈表明存在天然气水合物。与经典观测相反,Moby-Dick BSR 从西向东异常地向海底倾斜 150 m,这与向北变浅的海底相矛盾。我们认为,浅滩 BSR 的可能原因是整个盆地的气体混合物逐渐变化,西部含有较重碳氢化合物的气体向东部过渡为甲烷气。我们的研究表明,这种异常的 BSR 可以通过在盆地尺度上影响 GHSZ 形状的气体混合物的逐渐变化来控制。
更新日期:2021-11-23
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