Quantitative seismic geomorphology of Pliocene and Miocene fluvial systems in the northern Gulf of Mexico, U.S.A.

Quantitative seismic geomorphology (QSG) is a new direction in the analysis of seismic data that will create a step-change in our knowledge, characterization, and understanding of older clastic environments. QSG is defined as a quantitative analysis of landforms, imaged in 3-D seismic data, for the purposes of understanding the history, processes, and fill architecture of a basin. Built upon a foundation of seismic stratigraphy and sequence stratigraphy, QSG uses 3-D seismic data integrated with core and logs to investigate the nature and architecture of reservoirs through quantitative data collection on the morphometrics, and through analyses of the spatial and temporal variability of reservoirs. In the northern Gulf of Mexico (Vermillion Island and South Marsh Island) shelf study area, 902 km (super 2) of 3D seismic and 156 well-logging suites were analyzed to examine environments that included fluvial, deltaic, and shallow marine, as well as deeper-water shelf-edge, slope, and fan systems. Parameters measured include element sinuosity, meander wavelength and arc height, channel, and valley width:thickness, meander-belt width, and rates and directions of meander migration. Lithologic data from well logs and core, as well as relationships derived through experimental and modern-systems study of similar deposits, have been used not only to ascertain relationships between morphic and petrophysical character but also to predict spatial distribution of reservoir elements. Three specific fluvial-incision classes--aggradational fluvial systems (Class 1), bypass fluvial systems (Class 2), and creeks and distributaries (Class 3)--were examined through QSG methods and were found to show their own unique sinuosity, channel widths, meander lengths and meander-belt widths. Volume of shale calculated from well data shows Classes 1 and 2 to each be unique in their fill type and show the width:depth ratios to have some correspondence to net sand. These results suggest an ability to utilize seismic facies morphometrics to identify fill type within fluvial incisions, similar to techniques employed in the classification modern fluvial systems.