ABSTRACT: 3-D Seismic Imaging and Direct Observations of Seafloor Features on the Upper Slope, Green Canyon Block 184 Federal Unit, Gulf of Mexico

SHEEDLO, MARK K., and DOUGLAS J. COOK, Conoco Inc., New Orleans, LA

Three-dimensional seismic data provide a valuable supplement to high-resolution acoustic data for imaging the sea floor. Detailed horizon-oriented 3-D seismic interpretation coupled with direct observation via the Johnson Sea-Link research submersible has provided new insight into the relationship between 3-D seismic images (attribute extractions) and hydrocarbon seep-related features. The use of 3-D seismic data also allows greater resolution of subtle structural and depositional patterns on the sea floor.

Hydrocarbon seep-related carbonate mounds, mud volcanoes, hydrate hills, and collapse depressions occur locally in areas of hummocky topography associated with slumping and shallow salt intrusions. Many of these seep-related features can be distinguished using 3-D seismic interpretation. Hydrocarbon seeps have highly variable seismic amplitude responses and are typically underlain by varying degrees of acoustically amorphous seismic "wipeout" zones. This may be due to the close association between gas-charged sea floor sediments, gas-hydrates, and authigenic carbonates at seep sites. In some cases, seep-related features are underlain by strong low impedance seismic events, which may correspond to the lower boundary of gas-hydrate stability.

Subtle near sea floor structural and depositional patterns are easily recognized using 3-D seismic data. Faults with throws of less than 10 m are clearly imaged using color sea floor amplitude displays. Amplitude variations at the sea floor in local intraslope basins reflect subtle changes in lithology. Slumps, sediment gravity flows, and associated feeder channels may be identified using a combination of dip and amplitude displays.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)