Published 1996 as part of Memoir 66
Copyright © 1996 The American Association of Petroleum Geologists.   All Rights Reserved.
 

The detection of shallow gas features on the northern Gulf of Mexico continental slope has been aided with a unique positively buoyant deep-towed subbottom profiler and side-scan sonar system. The tool provides high-quality, high-resolution seismic displays of the shallow (upper 75 m) stratigraphy and seafloor images (400-m swath) capable of resolving geologic features that may constrain exploration drilling or engineering development of potential petroleum reserves.

From the more than 20,000 km (~10,000 nmi) of deep-tow data collected, numerous encounters of shallow gas features have been made. Gas and other fluid vents have been seen on the seafloor in association with seafloor and shallow buried fault systems. In some cases, vents have been identified by distinctive seafloor topography expressed as hills and mounds and by seafloor depressions, craters, and blister-like features. No distinctive topographic irregularities occur at other seafloor vent areas, which are identified primarily by the seismic character of the records. Shallow subsurface gas has been identified by the amorphous and wiped-out character of stratified sequences on subbottom profiler data and by high-amplitude "bright spot" reflections within sediment packages. Gas flow, both vertically along fault planes and laterally along permeable sediment layers, can be identified from these types of data.