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A New Modeling Approach for Turbidite Stratigraphic Trap and Reservoir Distribution Prediction: Examples Using Deepwater Systems of the East Coast Basin, New Zealand


Sediment bypass is a key process in gravity flow dynamics due to its role in the distribution of sediment across shelf-to-basin slope profiles. It has the potential to control turbidite reservoir presence, and the development of up-dip stratigraphic pinch-out traps through the formation of sand bodies such as ‘detached lobes’ that are disconnected from up-dip sands (e.g. The Buzzard Field, UK North Sea). Therefore, understanding the controls on sediment bypass is important to make predictions of reservoir quality zones and the integrity of bypass-related traps. Although existing approaches provide criteria to identify and model partial deepwater sediment bypass, it is still difficult to predict whether any sectors of the flow pathway are subject to complete bypass. This study aims to create a screening tool through the numerical modeling of sediment bypass and applied case studies to aid up-dip stratigraphic pinch-out trap risking and support reservoir distribution predictions in deepwater settings. We use a sediment transport model that assesses sediment bypass likelihood accounting for the grain size distribution in the flow and sediment concentration as a function of the slope gradient. Here we show the results from the application of the model in an intra-slope system using bathymetry from the East Coast Basin (ECB). Work in the ECB highlights the importance of deepwater canyons both as bypass conduits and for their potential to aid up-dip pinch-out trapping. Analysis of sediment bypass along inferred delivery pathways shows that: 1) the degree of bypass by flows transporting reservoir grade particles is controlled by local changes in the seafloor gradient, here dominantly tectonic structures, which occur with ridge-like morphologies and adjacent lows; 2) the deposition of reservoir grade sands occur in localized mid-slope lows with low gradients; 3) the profiles of bypass followed by deposition in lows provide an ideal setting for up-dip stratigraphic trapping. This analysis allows us to predict areas of slope accommodation that may be starved or well supplied with reservoir grade sandstone and can serve as a proxy for the potential reservoir distribution and up-dip stratigraphic trap occurrence in intra-slope subsurface systems of the ECB, and elsewhere. Furthermore, the methods developed here may act as a powerful screening tool for prospective deepwater exploration areas.