DYNAMICS OF INTRASALT MECHANICAL STRATIFICATION DURING ACTIVE DIAPIRISM: INSIGHTS FROM NUMERICAL MODELING

The kinematics and dynamics of layered evaporite sequences during active diapirism and the associated sediment deformation in the overburden are not well understood due to limited outcrop availability or well exposed natural salt diapirs and the difficulty to trace laterally continuous internal stratigraphic strain markers from 3D seismic data. Furthermore, the consequence of heterogeneity in rheological behavior, competency contrast and density inversion of layered evaporite sequences and the overburden on the resulting kinematics and dynamics during active diapirism has not been documented. In this study, a 2D forward numerical model based on plane strain finite element analysis is utilized to simulate processes of active diapirism by mechanisms of upbuilding and displacement loading. The overburden sediments are modeled as elasto-plastic, ductile intrasalt layers as visco-elastic and brittle intrasalt layers as visco-elasto-plastic rheologies respectively.

The numerical results show flow rate and diapir growth decreasing with increasing viscosity and number of embedded brittle intrasalt layers. This results in asymmetric active diapirs and relatively unstrained upturned flaps flanking crestal grabens within the overburden. Similarly, intrasalt competency contrasts has no significant effect on the internal deformation style of the layered evaporite sequences and associated sedimentary overburden. Flow folds adjacent to active diapirs comprised of intrasalt layers are attributed to inhomogeneous shear induced by buoyancy forces during active diapirism without displacement loading. Insights from these results may improve risk assessment for hydrocarbon exploration prospects, reducing drilling risks when subsalt reservoirs are targeted and locating salt welds as potential leak points of evaporite seals as the diapir matures.