Temporal and Spatial Evolution of a Transient, Fault-Controlled Thermogenic Hydrate System at Woolsey Mound, Gulf of Mexico

Abstract:

Woolsey Mound, located at Mississippi Canyon Lease Block 118 (MC118) in the north-eastern Gulf of Mexico, is a one-kilometer diameter carbonate mound where gas hydrate outcrops at the seafloor. To characterize and monitor the gas hydrate venting activity at this cold seep, a multidisciplinary seafloor observatory, Gulf of Mexico Hydrates Research Consortium (GoMHRC), was established in 2001. Woolsey Mound sits on an allochthonous salt body which is connected to the hydrate mound through a network of four shallow crestal faults. The seafloor morphology of the Woolsey Mound has been divided into three crater complex -SE, SW, and NW crater complex. Further investigation of this mound confirmed the presence of gas hydrates in shallow sediments by coring and 3D seismic reflection data.

In this study, we characterize the temporal and spatial evolution of gas hydrates at Woolsey Mound under natural perturbations using 3D seismic reflection data. Four collocated 3D seismic data collected over a span of 14 years (2000 to 2014) were analyzed to study this transient, fault-controlled gas hydrate system. We applied a ‘cross-equalization’ method to minimize the amplitude differences arising from variations in acquisition parameters. The resulting residual amplitudes are hypothesized to represent the true changes in pore fluid content over time. Our results indicate a significant volume of gas hydrate that had dissociated in 14 years. The dissociated hydrates show a close spatial association with subsurface permeable features such as faults, buried channels, turbidite lobes, etc. The SE crater complex has been the most active hydrate venting site whereas the SW crater showed the least amount of venting activity. The results of this study will add to our present understanding of hydrate evolution and its impact on ongoing carbon sequestration projects in the Gulf of Mexico, ocean chemistry, and climate change.