ABSTRACT: Identification of Deltaic Facies with 3-D Seismic Coherency

LOPEZ, JOHN A., NORM L. HASKELL, SUSAN E. NISSEN, and MIKE S. BAHORICH

A new 3-D seismic coherency technique developed by Amoco allows high resolution stratigraphic interpretations from average quality 3-D seismic data. Two deltaic examples from the Gulf of Mexico are documented.

A coherency time slice corresponding to a Pleistocene surface at approximately 4000 ft depth, displays a complex system of channels. A comparison of Pleistocene channel geometry with the modern Mississippi Delta suggests the presence of a paleo-Mississippi trunk channel and its associated distributary channels. Apparent lateral accretion and point bar development are observed on the coherency slice. This interpretation is confirmed using seismic profiles and well log data.

Coherency time slices between 2500 to 3400 ft depth show an elongate region of low coherency. A seismic profile down the axis of the feature shows a generally chaotic seismic character with a number of steep-sided blocks apparent. The shape and size of the low coherency features in map view, its seismic character, and its thickness suggests that this feature is the head of a submarine canyon produced by mass wasting, similar to the Late Pleistocene Mississippi Canyon. The blocks identified on the seismic profiles are proposed to be slump blocks. Block faces with low amplitude, but relatively high coherence, which are not evident on standard seismic time slices, can be seen on the coherency time slices. These slump blocks produce a distinctive mottled coherency pattern.

AAPG Search and Discovery Article #90941©1997 GCAGS 47th Annual Meeting, New Orleans, Louisiana