Spatial distribution of gas hydrates from high-resolution seismic and core data, Woolsey Mound, Northern Gulf of Mexico

Abstract

Integration of new jumbo piston cores with high-resolution seismic reflection data provides the first documentation on the subsurface distribution of gas hydrates at a deep-water cold seep. The study area, Woolsey Mound is a carbonate–hydrate mound of thermogenic origin, in the northern Gulf of Mexico where salt tectonics dominate the regional structure. Two typologies of unconventional seismo-acoustic data were used in this study: 1) surface-source deep-receiver (SSDR) data and 2) AUV-borne chirp sub-bottom profiler data. Correlation of the coring results with seismic interpretations supports the hypothesis that distinctive seismic brightening (high frequency scattering) present in the SSDR records may indicate the presence of solid hydrates. This suggests that such unconventional seismic survey may be prospective for mapping gas hydrates in complex deep-water settings. Coring results revealed the nature of the shallow gas hydrate system to be dominated by fine-grained sediments. Gas hydrates were found exclusively in fracture porosity in the vicinity of a major active fault. We present a model for Woolsey Mound where shallow gas hydrates are systematically distributed along segments of faults intersected by transit of thermogenic hydrocarbons. This dual nature of the faults being both gas hydrate reservoirs and gas migration routes suggests a very dynamic hydrate stability field for this site.