REGIONAL-SCALE SALT TECTONICS MODELLING: BENCH-SCALE VALIDATION AND EXTENSION TO FIELD-SCALE PREDICTIONS

The role of salt on the evolution of West African continental margin has been investigated by many researchers using both bench-scale experiments and seismic observations. For instance, Fort et al., 2004, indicates that regional-scale analogue bench-scale experiments of the Angolan margin comprises a complex system with an upslope extensional domain with sealed tilted blocks and extensional diapirs and a downslope contractional domain with late-stage squeezing of diapirs accompanied by folding and thrusting.

Numerical modelling procedures have the potential to provide additional insight into the evolution of these salt driven passive margins, through an integrated modelling framework that accounts for the evolution of the internal state of the rock formation. This necessitates the concurrent computation of displacement, fluid pressure and temperature history, together with additional variables dependent upon the specific physics included in the model.

This paper presents research regarding a computational approach for forward modelling complex structural evolution, with particular reference to passive margins driven by salt tectonics. The formulation adopts a Lagrangian finite element method, complemented by automated adaptive remeshing techniques and elasto-viscoplastic sediment constitutive models based on extended critical state concepts. The formulation is featured within ELFEN, a finite element package, which specialises in paleo-structure evolution via modelling the burial and deformation history of sediments from initial deposition to the current-day state.

Numerical simulations are presented for regional bench-scale models based on the experiments presented by Fort et al., 2004. As no “seeding” of imperfections is used in the models, it is shown that the behaviour observed in both the compressional and extensional zones of the analogue models arises naturally from the imposed physics incorporated in the numerical simulations. A final discussion regarding the extension of these models to the field-scale is made, whilst highlighting important practical issues regarding thermal effects and mechanical/chemical compaction.

Fort, X., Brun J-P., Chauvel, F., Salt tectonics on the Angolan margin, synsedimentary deformation processes. AAPG Bulletin 88, 1523-1544, 2004.