Seismic Geomorphology and Seismic Stratigraphy of Deep-Water Depositional Elements

By

 Henry W. Posamentier¹

(1) Anadarko Canada Corporation, Calgary, AB

 Analyses of 3-D seismic data can yield significant insights with regard to spatial and temporal relationships of near-seafloor depositional elements in deep-water settings. These analyses can be based on a broad range of horizon attributes, such as amplitude, time/depth structure, dip azimuth, dip magnitude, curvature, and roughness, as well as interval attributes such as frequency and amplitude distribution, and seismic facies based on waveform. The great complexity of deep-water depositional environments can be simplified by grouping depositional elements into five major categories: 1) turbidity-flow leveed channels, 2) channel-overbank sediment waves and levees, 3) frontal splays/distributary channel complexes, 4) crevasse splay complexes, and 5) debris-flow channels, lobes and sheets. Each depositional element type displays a unique morphology and seismic-stratigraphic expression. Their reservoir architecture is a function of the interaction between sedimentary process, sea-floor morphology, and sediment grain size distribution.

Turbidity-flow leveed channels can range from nearly straight to highly sinuous; channel meanders in most instances migrate down-system. In some instances, high-sinuosity channels are associated with channel-overbank sediment wave development, especially in association with outer channel bends. Where levees can no longer be resolved seismically, high-sinuosity channels feed frontal splays/low-sinuosity distributary channel complexes. Low-sinuosity distributary channel complexes commonly are expressed as lobate sheets. A variation on frontal splays are crevasse splay deposits, which comprise smaller lobeforms associated with levee crevasses commonly located at channel bends. Debris-flow deposits can form low-sinuosity channel fills, elongate lobes, and sheets and are characterized seismically by contorted, chaotic, low-amplitude reflection patterns that commonly overlie striated/grooved pavements.