Using RMS amplitudes from forward seismic-reflectivity modeling of channelized deep-water slope deposits to inform stratigraphic interpretation and sub-seismic scale architecture, Tres Pasos Formation, Magallanes Basin, Patagonia, Chile

Abstract

Deep-water slope channels outcropping in the Tres Pasos Formation of the Magallanes Basin in southern Chile are used as the foundation of a forward seismic-reflectivity modeling study to better inform stratigraphic interpretation. The multi-scale architecture of deep-water slope channels is often difficult to interpret from low resolution seismic-reflectivity surveys. Valuable insight can be gained from forward seismic-reflectivity modeling using multiple-scales of architecture as building blocks (i.e., channel elements stacking into channel complexes) to provide insight into subsurface interpretation. Forward seismic-reflectivity models of channel elements with sub-meter scale heterogeneity are interrogated for RMS amplitude and apparent thickness as a function of true stratigraphic thickness and net sand thickness. Relationships between interpreted variables from the forward models (RMS amplitude and apparent thickness) compared to measured variable from the input models (true stratigraphic thickness and net sand thickness) provide recognition criteria for interpreting building blocks in subsurface seismic-reflectivity data. This study shows that decreasing RMS amplitude for constant apparent thickness is primarily controlled by vertically juxtaposed facies between multiple stacked channel elements. Furthermore, laterally stepping and vertically aggrading channel elements increase confidence in stratigraphic interpretation whereas laterally migrating channel elements are harder to delineate. An increase in frequency tends to improve interpretation of net sand thickness for multiple channel elements informing interpretation of lateral facies changes. Results from this study also show that RMS amplitudes and apparent thickness show patterns to help differentiate channel element stacking configurations and can be tied back to the known model variables, true stratigraphic thickness and net sand thickness. However, interpretation of exploration scale data, specifically RMS amplitude and apparent thickness interpretations is complicated by interfering reflections at increased frequency, complicating the recognition of multiple channel elements within a channel complex set.