Print this page ABSTRACT: Using a hybrid 
seismic
attribute to differentiate lithologies and facies
in a deltaic system, Texas Gulf Coast, U.S.A.
Carr, David L.1, M. Turhan Taner2,
and J. Todd
Mitchell2
(1) Geoscience Consultant, Austin, TX
(2) Rock Solid Images, Houston,
TX
A "hybrid seismic attribute" can be constructed by combining several physical
and geometric seismic attributes such that the new hybrid enables the interpreter to
differentiate lithology and facies. In our example, a hybrid attribute was constructed to
distinguish lithofacies commonly encountered in deltaic depositional systems, where
varying amounts of sandstone, mudstone and carbonaceous facies occur, and are
intercalated in a variety of bedding styles (e.g., thin-bedded continuous; thick-bedded
discontinuous; massive; etc.).
Isolated sandstone gas reservoirs (up to 50 feet thick) in the basal part of the
Vicksburg Formation are encased in several hundred feet of marine shale. The reservoir
sandstones were initially detected by examination of the hybrid attribute volume. After
calibration with well logs and core information, we were able to map lithofacies and
reservoir properties in detail.
The hybrid attribute map revealed a complex 'valley' representing a fluvio-distributary
channel system that fed a coastal strandplain. Three seismic attribute facies were
identified: (1) Sinuous patterns that meander from one side of the valley to the other. Interpretation:
Abandoned channel mudstones and lignite; (2) 'Crescents' that are tucked within the
concave portions of Facies 1. Interpretation: Point-bar and active distributary
channel reservoir sandstones; (3) Valley-adjacent, mottled areas with subtle dip- and
strike-oriented textures present locally. Interpretation: Composites of delta-plain
mudstones and crevasse splay sandstones, plus older strandplain sandstones.
The hybrid seismic attribute enabled a high-resolution determination of lithofacies,
including reservoir sandstone facies, that could not have been accomplished on the basis
of standard seismic
amplitude extractions and well logs.
AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia