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Use of High-Resolution 3-D Seismic Data to Evaluate Quaternary Valley Evolution History During Transgression, Offshore San Luis Pass, Gulf of Mexico

Abstract

A novel, shallow-investigation, high-resolution 3D (HR3D) seismic acquisition system has been employed, for the first time in the Gulf of Mexico, to characterize storage potential and de-risk targets for CO2 sequestration. HR3D data can image detailed depositional, architectural, and structural features in the shallow subsurface that have previously been below seismic resolution and/or excluded from industry surveys, which are optimized for deeper targets. One HR3D survey is located just offshore from San Luis Pass, TX and covers an area of 31.5 km2. The dataset images the shallow subsurface with an unprecedented level of detail – peak frequency of approximately 150Hz (8 25m cables, spaced at 12.5m, 6.25m by 6.25m bin size). Imaged within this dataset at ~100ms, is a mappable erosional unconformity that is interpreted to be associated with the Brazos River system during the last glacial-eustatic lowstand and following Holocene transgression. Through the analysis of stratal slices and the geometries of the valley form and its dendritic features, we explore the evolution history of the valley system during a transgressive episode. Observations indicate that the system evolves from a lowstand meandering channel with clear point-bar deposits to a transgressive estuary characterized by dendritic tidal features that is eventually flooded. This is an exceptional 3D example of a lowstand to transgressive transition and the sedimentary processes that dominate in each instance.