Predictive Organization of Intra-Slope Basin Submarine Fans
Jacob Covault, PhD
Research Scientist, Bureau of Economic Geology
The lateral continuity and vertical connectivity of architectural elements of submarine fans are important uncertainties in reservoir characterization and modeling. The distal, basin-floor deposits of submarine fans have been interpreted as laterally extensive sheets. However, intra-slope basins characterized by high gradients (>0.5°) and slope breaks show more complex three-dimensional (3D) stratigraphic architecture, which can have significant impact on reservoir performance. We use 3D seismic-reflection data (~35 Hz dominant frequency) in the subsurface offshore Trinidad to document the stratigraphic architecture of a submarine fan in a tectonically active intra-slope basin characterized by high gradients and slope breaks. Leveed channels avoid mass-transport complexes and mud volcanoes as they traverse a high-gradient (~1°) reach of the continental slope. Channels transition to a field of 10^2-10^3 m wavelength and 10 m wave height scours at a slope break (<0.5°). Some of the scours are aligned in linear trains and resemble erosional features of the channel-lobe transition zone documented with higher-resolution acoustic imaging of the seafloor and shallow subsurface globally. Stratigraphically overlying the channel-lobe transition zone, scours coalesce to form low-relief (~10-20 m), compensationally stacked channels. Channel mouths transition to scours and depositional lobes (several km long). The stratigraphic architecture of the intra-slope basin submarine fan, comprising channel-fill, levee-overbank, lobe, and channel-lobe transition zone architectural elements, reflects repeated cycles of channel avulsion, compensation and modification of initial deposits, and unconfined deposition at the channel mouth. Furthermore, we expect that the preservation of the channel-lobe transition zone and its scours are important considerations in reservoir characterization in other tectonically active continental margins with rapid aggradation of a submarine fan. In these settings, high gradients and sediment supply can promote local intra-slope coarse-grained turbidite deposition at slope breaks where internal hydraulic jumps (i.e., transition from densimetric Froude supercritical to subcritical flow) in turbidity currents govern the stratigraphic architecture and evolution of submarine fans. We evaluate our geologic model with DionisosFlow forward stratigraphic modeling, which demonstrates multiple scales of compensational stacking and we consider the impact of connectivity of architectural elements on fluid flow behavior during hydrocarbon production. These interpretations inform the modeling and prediction of 3D heterogeneity of intra-slope basin submarine fans and illustrate the importance of detailed characterization in order to understand reservoir connectivity.
Dr. Jacob Covault is a research scientist and leader of the Quantitative Clastics Laboratory (QCL) at the Bureau of Economic Geology, The University of Texas at Austin. His expertise is the sedimentology and stratigraphy of deep-water depositional systems, and source-to-sink sediment dispersal. Jacob’s work addresses challenges in the exploration and development of natural resources, namely reservoir presence and quality prediction in frontier basins, as well as reservoir connectivity and heterogeneity. Prior to his present position at the QCL, Jacob was a senior research scientist at Chevron Energy Technology Company and served the Department of the Interior at the U.S. Geological Survey. He received Ph.D. and B.S. degrees in geological and environmental sciences at Stanford University, where he played football from 1999 to 2003. Jacob has published peer-reviewed research papers and scientific conference abstracts on petroleum geology, reservoir characterization, sedimentology, stratigraphy, basin analysis, Earth-surface processes, and marine geology. Jacob is the recipient of the 2017 SEPM Wilson Award in recognition of “Excellence in Sedimentary Geology by a Young Scientist.”