Constraining Gas Hydrate Occurrence in the Northern Gulf of Mexico Continental Slope: Fine Scale Analysis of Grain-size in Hydrate-bearing Sediments

Within the subseafloor, methane hydrates form within the gas hydrate stability zone (GHSZ). Two areas within the Gulf of Mexico (GOM) were investigated in this study: Keathley Canyon and Atwater Valley. The GOM contains an underlying petroleum system and deeply buried, yet dynamic salt deposits. Salt tectonics and fluid expulsion upward through the sediment column lead to the formation of fractures, through which high salinity brines migrate into the GHSZ, destabilizing gas hydrates. Originating from the thermal and biogenic degradation of organic matter, thermogenic and biogenic hydrocarbons also migrate to the seafloor along the GOM’s northern slope. Gas hydrate occurrence can be controlled by either primary permeability, forming in coarse-grained sediment layers, or by secondary permeability, forming in areas where hydrofracture and faulting generate conduits through which hydrocarbon-saturated fluids flow. The goal of this study is to determine the relationship between grain-size, permeability, and gas hydrate distribution. Grain-size analyses were performed on cores taken from Keathley Canyon and Atwater Valley in the GOM, on sections of cores that both contained and lacked gas hydrate. The initial results indicate that gas hydrate occurrence in Keathley Canyon and Atwater Valley is constrained by secondary permeability, being structurally controlled by hydrofractures and faulting that act as conduits through which methane-rich fluids flow.