Slope-Fan Depositional Architecture From High-Resolution Forward Stratigraphic Models

Abstract

Submarine fans in tectonically active continental-slope basins are targets of petroleum exploration and production. These slope fans commonly comprise compensationally stacked sandy and muddy architectural elements, including mass-transport deposits, weakly confined to distributary channel-and-lobe deposits, and leveed-channel deposits. The lateral continuity and vertical connectivity of these architectural elements are important uncertainties in reservoir characterization that influence fluid-flow behavior during hydrocarbon production. Here, we use a simple forward stratigraphic model to reproduce the large-scale stratigraphic patterns and illuminate the likely distribution of finer-scale, sub-seismic heterogeneity in a slope fan. We used 3D seismic-reflection data in the tectonically active Columbus basin, offshore Trinidad, to document the Pleistocene stratigraphic architecture and evolution of a submarine fan across a stepped slope profile. We interpret that sediment-gravity flows avoided pre-existing mass-transport-deposit topography, and formed compensationally stacked channel-and-lobe deposits. Once the stepped slope profile was healed by deposition, a leveed channel promoted bypass of sediment to the Atlantic abyssal plain. We then evaluated our interpretation of compensation with a series of DionisosFlowTM forward stratigraphic models. A reference-case model generally matches the thickness trend of our seismic-stratigraphic interpretation; it also produced similar large-scale patterns of compensational stacking and depocenter evolution. However, varying the time step impacts the heterogeneity of the model. Shorter time steps are characterized by less sediment accumulation, which results in less sediment diversion during the subsequent time step, more gradual migration of channel deposits, shorter offset distances of depocenters, and shorter length-scale heterogeneity compared to longer time steps. Furthermore, our results suggest that relatively simple diffusion-based models can produce realistic compensation patterns. We also evaluate the impact of environmental parameters on the depositional architecture through experimental designs and automated multi-simulations. Preliminary results inform the prediction of 3-D sub-seismic heterogeneity of slope fans and demonstrate the value of integrated subsurface characterization and forward stratigraphic modeling to understand the range of reservoir connectivity and quality in such settings.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018