Forward Sediment Modeling of Carbonate Platforms and a Survey of Genetic Controls

Lisa A. Roehl and Sherry L. Becker
ExxonMobil Upstream Research Company, Houston, TX

Key factors in the development of a carbonate system include the growth rate of carbonate-secreting organisms, water depth and energy level at the site of deposition. These factors are impacted by antecedent topography, subsidence (local tectonism) and eustatic sea level. Forward stratigraphic models were built to study the impact of subsidence and antecedent topography on the geometry and distribution of depositional sequences. Models were constructed for isolated platforms, ramps and rimmed margins using Dionisos (Diffusive Oriented Normal and Inverse Simulation of Sedimentation), a forward sediment model developed by the French Institute of Petroleum (IFP).

Input sediment parameters utilized measurements from modern environments. To test modeling capability where environmental conditions are better constrained, an initial model was constructed for Caicos Platform (British West Indies). Results show that the model detects each major sediment type of mapped depositional environments on the Caicos Platform.

Additional models were developed to simulate a rise in sea level (using a symmetric sinusoid sea level curve) for three major platform types: isolated platform, land-attached rimmed shelf and land-attached ramp. For Isolated carbonate platforms, results show that late lowstand and early transgressive deposits accumulated on the windward-facing margin whereas highstand deposits dominated the remaining platform area. For land-attached, rimmed platforms the proportion of late lowstand/early transgressive deposits to highstand deposits increased with platform width. Finally, in land-attached ramp systems the proportion of late lowstand/early transgressive deposits increased with progressively steeper ramps while low-angle ramps were dominated by stacked highstand deposits.