Temporal and spatial characterization of a thermogenic, fault-controlled gas hydrate bearing system, Woolsey Mound, Gulf of Mexico

Abstract

Woolsey Mound, located at Mississippi Canyon Lease Block 118 (MC118), is the site of the Gulf of Mexico hydrate research consortium’s seafloor observatory where gas hydrates outcrop at the seafloor. The presence of gas hydrates in the mound was confirmed directly by coring and indirectly by 3-D seismic reflection data. Craters, pockmarks, chemosynthetic communities, and authigenic carbonates populate the seafloor at Woolsey Mound. Each crater is characterized by a network of shallow crestal faults that connect the hydrate mound to the underlying allochthonous salt body. We characterized the temporal and spatial evolution of gas hydrates at Woolsey Mound under natural perturbations using four collocated 3-D seismic reflection datasets that span over 14 years. Data acquisition differences embedded in the datasets arising from variation in geometry, sample rate, and phase, were minimized using the ‘cross-equalization’ method. Our results indicate that hydrate formation and dissociation vary both temporally and spatially in close connection to the shallow crestal faults. Evidence of gas hydrate dissociation was observed over a period of three years (2000-2003) where major dissociation occurred along the southern portion of the crestal fault in the southeast crater. The dissociation is less prominent in the southwest crater. Evidence of methane venting was observed between 2000 and 2010, which is mostly concentrated in the southeast crater. The residual amplitude anomalies observed between 2000 and 2014 in the mound were mostly positive, implying the methane venting had increased significantly. The positive anomalies were correlated with the methane seepage recorded in 2011. Our results show the evolution of a fault-controlled gas hydrate system in the northern Gulf of Mexico which would aid in assessing its impact on the seafloor.