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Identification of Deltaic Facies with 3-D Seismic Coherency and the Spectral Decomposition Cube: A Study Form South Marsh Island Area, Gulf of Mexico
John A. Lopez (1), Greg Partyka (2), Norm L. Haskell (2), Susan E. Nissen (2)
New 3-D seismic attributes developed by Amoco allow high resolution stratigraphic interpretations from 3-D seismic data (Bahorich and Farmer, 1994,1995; Haskell et al., 1995; Nissen et al., 1995; Ortman and Wood, 1995; and Lopez et al., 1996). Seismic coherence algorithms are useful for structural and stratigraphic mapping and have been previously described. A new technique called Spectral Decomposition Cube is useful for mapping stratigraphy or reservoir delineation (Partyka, 1997). The Spectral Decomposition Cube is a Fourier transform applied to individual traces within a window around an interpreted horizon. Examination of the amplitude maps of specific frequencies can accentuate geologic features that are "tuned" to specific frequencies. Regional 3D seismic in the Gulf of Mexico illustrate detailed deltaic stratigraphic patterns. The potential usefulness of these frequency defined map attributes is demonstrated by mapping of a series of shallow horizons on a speculative seismic survey in the South Marsh Island area of the offshore Louisiana, Gulf of Mexico.
The coherency time slice corresponding to a Pleistocene surface at approximately 1200 m (4000 ft) depth, displays a complex system of deltaic channels. The nearly identical map of channels can be seen on the Spectral Decomposition Cube at 18 Hz. However on the Spectral Decomposition image additional subtle features are seen which help complete the stratigraphic interpretation. A comparison of Pleistocene channel geometry with the modern Mississippi Delta suggests the presence of a paleo-Mississippi trunk channel oriented north-south and its associated distributary channels.
Coherence algorithms and spectral decomposition cubes are attributes of a rapidly developing expanding family of seismic attributes which are particularly helpful for 3D seismic interpretation of map-view patterns of faults or stratigraphy. Their usefulness is increased when used in combination and with traditional mapping techniques. Although low signal to noise of the seismic may limit the usefulness of these attributes in some areas, rapid advances in seismic quality and more robust algorithm development should significantly expand their usefulness.
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