ABSTRACT

A self-consistent quantitative model has been constructed for the intertwined evolution of both salt and sediments, which automatically provides information on the changing bed geometries with time in a manner guaranteed to be consistent with present-day observations of salt bodies and sediment geometries. Instead of trying to specify a large number of mechanical properties in order to calculate the stress in the evolving salt-sediment system, and then attempting to calculate the corresponding strain, the procedure simplifies this process by reversing the order: (1) determine the strain; (2) define the response of the sediments to stress (e.g., elastic); and (3) calculate the corresponding stress.

A synthetic case exemplifies how the strain/stress patterns in the sediments depend on the evolving geometry of the salt through time. A large salt overhang results in massive strain next to, and immediately below, the overhang due to the horizontal spreading of the salt and the associated void space created near the salt stem, which the sediments deform to fill. Therefore, sediments below the overhang "slide" into the space created as the total salt structure feeds the overhang development.

From the calculated strain behavior of the sediments, the stress associated with the strain can be evaluated once the spatial variations of the sedimentary Lame constants are specified. When the Coulomb criterion for failure is included, the timing and development of sedimentary fracturing can be calculated. Knowledge of the spatial fracture pattern and its temporal evolution is crucial to the evaluation of hydrocarbon migration pathways and trap development near salt structures. The timing of oil generation, which depends on the thermal history of the sediments, can then be compared and contrasted to the timing of migration through the fractured regime.