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Seismic Visualisation of Mixed-Influence Coastal-Deltaic Depositional Systems

Abstract

Recognition of mixed processes on coastal-deltaic systems end members (relative power of W- wave, T -tide and F-fluvial processes) is important for both exploration & reservoir characterization. Mixed-influence systems impart asymmetry and heterogeneity that impact prediction of subsurface lithology (facies), static modelling of various connectivity scenarios, and ultimately exploration to development well planning. Numerous detailed studies of these mixed-influence systems from modern analogs, outcrop, core, & log data requires calibration with high resolution seismic visualization. Although typical stacking of genetic units (5–25m parasequence-scale) is at or below the resolution limits of most 3D seismic data, focused seismic stratigraphic workflows can image detailed geomorphic plan-forms, which reflect features at the limits of detection (<10m). A range of seismic stratigraphic workflows are illustrated (single and multiple datum's, horizon slicing, flattening, optical stacking, channel/feature chasing, and attribute calculations) with a variety of example seismic datasets. These workflows can produce detailed images of complex facies juxtapositions at or near the detection limit. Key characteristic plan-form features at element to complex scales include the following: 1. High to low reflectivity, continuous elongate arcuate, divergent to subparallel reflections (either convex or concave in a basinward direction), indicative of wave-dominated (W), to wave-dominated, but tide-influenced (Wt) strand-plains & associated down-drift chenier-plains (Tw). 2. High reflectivity, continuous & sinuous channel-form reflection features adjacent to sets of convex recurved-lineations, interpreted as tide-influenced estuarine (Tf) or distributary channels (F, Ft). 3. Transparent seismic reflections with internal channel-forms, & dendritic or reticulate planforms, indicative of tide-dominated shorelines including tidal flats & tidal creeks (T, Tw, Twf). 4. High to low reflectivity, continuous or discontinuous, low- to high-sinuosity channel-form reflections, either isolated or amalgamated, indicative of fluvial-dominated channel belts & abandoned meander loops (F, Ft), within a background of continuous to discontinuous reflections, representing the alluvial or coastal-deltaic floodplain. These patterns are key indicators of mixed-influences on coastal-deltaic deposits, impacting reservoir distribution & connectivity, and a basis for building static reservoir models.