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Using RMS Amplitudes Derived From Synthetic Forward Seismic Models of Channelized Deep-Water Slope Deposits to Inform Stratigraphic Interpretation, Tres Pasos Formation, Magallanes Basin, Chile


Deep-water channel heterogeneity from bed- to composite channel complex- scale can significantly impact reservoir delineation. The resolution of seismic typically used in industry to image these reservoirs (20 – 50 Hz) is unable to resolve important detail below the composite channel complex scale. Synthetic seismic-reflectivity modeling focusing specifically on amplitude response can aid in interpreting lithofacies, channel base morphologies and stacking patterns. The production of synthetic seismic profiles using known internal architecture for a single channel element and patterns of multiple stacked elements provide templates to aid in interpreting sub-seismic uncertainties critical for effective exploration and development in channelized deep-water reservoirs. A bed-scale model of a single channel element was created based on slope channel deposits of the Cretaceous Tres Pasos Formation in the Magallanes Basin of southern Chile. From this model, synthetic seismic-reflectivity models were created using two sets of analogous rock properties (deep Gulf of Mexico and shallow West Africa). RMS amplitude maps at different frequencies (20 – 180 Hz) were generated to elucidate changes in amplitudes as a function of channel fill thickness, intra-channel lithofacies distribution, and stacking patterns (including separation of successive channel fills). For a single channel element, a strong positive linear relationship between RMS amplitude and net sandstone thickness exists. The slope of this relationship and the magnitude of RMS amplitude decreases with increasing frequency, improving interpretation of internal channel fill and lateral facies distribution(s). The analysis was repeated for a composite channel complex (~100 m thick, ~2.5 km long segment), composed of 18 channel elements. Results show that at frequencies above 90 Hz, channel width, internal lateral facies distribution, and channel seperability can be determined with a high level of confidence; however, only stacking relationships can be resolved down to 60 Hz. RMS amplitude in models below 60 Hz point to laterally migrating versus vertically aggrading channel elements, however, direct interpretation of elements is not possible. This study shows a direct relationship between net sandstone thickness and RMS amplitude from the channel element level (above 90 Hz) to the composite channel complex (below 90 Hz) and provides a method for interpretation using patterns observed in forward models.