--> Seismic Reflectivity Modeling of Outcropping Deep-Water Slope Systems, Tres Pasos Formation, Magallanes Basin, Southern Chile: Implications for Reservoir Exploration and Development

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Seismic Reflectivity Modeling of Outcropping Deep-Water Slope Systems, Tres Pasos Formation, Magallanes Basin, Southern Chile: Implications for Reservoir Exploration and Development

Abstract

The stratigraphic expression of slope channel and channel-lobe transition zone (CLTZ) deposits is highly varied as a consequence of distinct formative processes, associated with turbidity current interaction with confined to unconfined seafloor morphology. Architectural element end members include low aspect ratio channel elements and higher aspect ratio sedimentary bodies that form in response to diminished confinement. The protracted evolution of each depositional setting results in distinct stratigraphic stacking patterns of sedimentary bodies. In outcropping slope deposits of the Cretaceous Tres Pasos Fm, Chile, a channel system outcrop (Location: Laguna Figueroa) consisting of 18 channel elements is considered. Elements are aggradationally stacked (120 m gross stratal thickness) with limited lateral offset (<150 m) amongst successive channels. Conversely, over a similar gross interval (110 m), CLTZ deposits (Location: Arroyo Picana) are characterized by variable sedimentary bodies, including channelforms and higher aspect ratio bodies that are not stacked in an organized pattern. Important considerations at the foundation of this research include: (1) How would these distinct stratal sections appear in 3D seismic data? (2) Would seismic reflections accurately portray the stratigraphic architecture evident in the outcrops? In order to answer these questions, 3D seismic reflectivity models (ranging from 180–15 Hz peak frequency) were constructed for both slope channel and CLTZ outcrops. The 18 stacked channel elements from the Figueroa outcrop can mostly be discerned at 180 Hz, however, at 30 Hz the amalgam of elements is manifest by 3 oversized channelform bodies, or “channel complexes”. Key seismic reflections are highly composite in nature, blending responses from the varied component elements. These 3 channel complexes represent a useful proxy for channelized sandstone distribution. However, predictable intrachannel facies patterns derived from outcrop characterization of channel elements (i.e., sandy axes to muddy margins) cannot be applied at the scale of the channelforms apparent in the seismic data. Likewise, complex stratigraphic architecture evident at180 Hz for the CLTZ outcrop is largely obliterated at 30 Hz. Although zones of thickest sandstone may be interpreted, the interconnectivity of the various depositional elements is highly simplified. Results from this research close the gap for sub-seismic scale reservoir quality interpretation.