Gas sources of marine gas hydrate systems and the critical role of fluid migration pathways in gas hydrate formation

Gas hydrate systems contain large quantities of methane that may originate from biogenic, thermogenic, or mixed sources. Fluid migration pathways, including gas chimneys, faults, inclined permeable strata and diapirs, are critical for transporting thermogenic gases at depth into gas hydrate systems in shallow subsurface. However, the role of these pathways in hydrate accumulation, particularly in systems dominated by biogenic or mixed gases, remains poorly investigated. This study integrates global case analyses of geochemical indicators of gas origin and geophysical signatures revealing spatial relationships between hydrate systems and migration conduits. Numerical modeling of hydrate accumulation history in the Gulf of Mexico Basin and the Qiongdongnan Basin further has been carried out. Results show that regardless of gas origin, in-situ biogenic gas alone is insufficient to form medium- to high-concentration gas hydrate. Fluid migration pathways are necessary for providing allochthonous gas. Generally, this study provides insights into the formation history of gas hydrate system and indicates that fluid migration pathways play a pivotal role in the formation of favorable gas hydrate systems, irrespective of whether the gas source is biogenic, thermogenic, or mixed.