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Process-Based Modeling of Sediments Deposition and Compaction in the Peïra Cava Sub Basin; Detailed Analysis and Sediments Distribution at Reservoir-Scale


Turbidity currents are the most important mechanism for the dispersal and deposition of sand in the deep-sea setting and thus the main phenomenon leading to the formation of oil and gas reservoirs in deep water deposits. Turbidity currents are difficult to study from the modern environment, while their laboratory representations are typically hampered by scaling issues, unrealistic geometries, and short durations. Computational fluid dynamic (CFD) is being developed to fill the gap between small and large scale, integrating data from theory, nature, and experiments. At the scale of individual beds the petrophysical characteristics, and hence hydrocarbon reservoir properties, are controlled by the depositional processes (e.g Barker et al. 2008) and an understanding of turbidite depositional process can be used to predict reservoir properties. A process-based approach is required to achieve a detailed prediction of reservoir properties at the bed scale (Janocko et al. 2012). The aim of the current study is to test the applicability of process-based modeling to predicting bed geometry and grainsize distribution in a single bed (Marker Unit 5, MU 5) from the Annot Sandstone, SE France. The particle size population input (80 μm, 200 μm, 400 μm and 1 mm in diameter) was guided by six available data-points distributed throughout the outcrop (Amy et al. 2007). The modeling required a seafloor surface to represent the base of this particular bed at the time of deposition. The available palaeo-bathymetry was the Base Annot Sandstone, whereas the MU5 bed is situated within the basin-fill. Thus, in a first phase, the basin-fill up to the MU5 bed was recreated performing subsequent numerical modeling starting from the base Annot Sandstone surface with subsequent modelling of compaction and isostatic bending after each flow simulation. Doing so, the base surface for the MU5 was recreated. In a second phase the process-based flow simulation of the MU 5 bed, starting from the so-recreated surface, was performed. The numerical results matched the field data both in thickness and sediments distribution. This demonstrates the capability of the software to deal with multiple grain sized turbidity currents in order to reproduce the depositional pattern and proving to be a tool for analyzis of hydrocarbon reservoirs at all scales, from regional scale to single-layer scale.