Physics-based forward numerical models have a wide variety of applications in areas such as geomorphology, stratigraphy, and geologic modeling. In this paper, the ExxonMobil process-based forward numerical models for simulating shallow and deep water depositional systems are introduced. Based on the physics of fluid flow and sediment transport, these models are capable of modeling many important natural geomorphic processes, such as channel initiation, lobe deposition, knick-point migration, channel avulsion, and formation of sedimentary waves, levees, and channel mouth bars.
A computer model was used to simulate East Breaks basin 4, which is the terminal basin of four interconnected intra-slope basins situated in the north-western Gulf of Mexico. An interpreted surface from a high-resolution 3D seismic survey was depth converted and used as the initial basal surface for simulations. The inlet location for turbidity flow also was interpreted from the seismic and provided to the computer model. A trial and error approach was used to determine the discharge of the flow as well as the volumetric concentration and the size distribution of particles in the flow. Simulation results were then converted to synthetic seismic and compared with actual seismic from the basin. The comparisons showed that the simulated sediment body geometries and stacking patterns closely resembled those observed in the seismic data.
Simulation results show that many of the complexities observed in such systems originate from the complex interactions between the evolving topography and the flow. The evolution of these systems often follows similar and predictable pathways. A common evolution pathway consists of following steps:
Flow expansion at the channel mouth;
Scouring in front of the channel mouth;
Development of channel mouth bars;
Local ponding of the flow by the channel mouth bar;
Accelerated growth of levees and the formation of knick-points; and
Subsequent avulsion and the extension of the channel.
This pathway appears to be scale invariant which could suggest a predictable distribution of sedimentary bodies in deltas and submarine fans.
The study has demonstrated that the forward numerical model is a powerful new geologic modeling tool. Prerequisites for effective modeling include: (1) accurate restoration of basin paleotopography; (2) realistic flow characteristics, including flow discharge and sediment concentration; or (3) estimates of sediment size distribution in the flow. These data are not obtained routinely from subsurface studies, and may not be obtained directly from subsurface data. However, they may be derived through integrated analysis of seismic volumes and well data. Including such analysis in the seismic interpretation and reservoir-characterization workflow is essential for the development and application of forward numerical models as next generation earth models.