Simulation of the Annot Turbidite System with the CATS Process-Based Numerical Model
The process-based Cellular Automata for Turbidite Systems model simulates turbiditic flows and associated sedimentary processes. Its aim is to reproduce detailed description of reservoir architecture and heterogeneity of deep-offshore fields. The model is based on cellular automata concepts: each cell of the regular mesh is an automaton whose attributes describe local physical characteristics of the bed and the flow. Neighboring automata exchange matter and energy through local interactions. Their energetic and physical states evolve trough time according to internal transformations. Local interactions and internal transformations are the local expression of chosen modelled physical processes: downslope flow, run-up due to kinetic energy, erosion and deposition of several lithologies and entrainment of ambiant water by the flow. The model is able to simulate different architectural elements such as erosive channels, levees, channel mud-plugs & lobes and their facies partitioning.
This model is applied to the Annot Sandstone Formation, a turbidite system of Eocene-Oligocene age outcropping in the Southern French Alps. The Annot syncline is fed by a detritic fan delta in its eastern boundary. It is composed of several units migrating westward on the underlying "Blue Marls" Formation affected by synsedimentary faults linked to the foreland activity. The syncline was completely filled by early Rupelian times, and began to spill over to the North into the Trois Évêchés-Chalufy basin via a narrow trough located close to the Grand Coyer.
The CATS model needs an initial topography, in this case the "Blue Marls" top surface. This palaeotopography was reconstructed with the gOcad modeler from the base surfaces of the Annot Sandstone units. The obtained topography is consistent with palaeocurrent directions and stratigraphic data measured on the field.
To simulate each unit, the physical parameters of the turbiditic flows (height, velocity, flow concentration of different lithologies) and their evolution through time are set by a trial-and-error process. Extension, thickness and lithological composition of the simulated results are checked against field data. Impact of a tectonically controlled topography on the flow behavior and the resulting facies architecture is also analysed.
The CATS model provides reservoir geologists with an efficient process-based tool to investigate quantitatively geometry, architecture and facies distribution of complex turbidite systems.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009