The Impact of Sea-Floor Topography on Sediment Fairway Distribution, Architecture and Reservoir Quality in Espiacute;rito Santo Basin, Brazil

Warchol, Michal¹; Dykstra, Mason; Janocko, Michal; Bakke, Kristina; Marcussen, Øyvind; Husmo, Tore; and Hadler-Jacobsen, Frode
¹[email protected]

Seafloor topography, together with sediment type and sedimentary processes, is one of the major controls on reservoir facies type, its architecture and reservoir quality distribution in deepwater settings. We present subsurface data showing how both static and dynamic seafloor topography has influenced the distribution of sediment fairways and ‘shadow zones’ in the deep-water Espirito Santo Basin, Brazil.

A first order control is the presence of a large margin-bounding fault at the shelf-edge along the western basin margin, which creates a bypass zone on the upper slope for coarse-grained deposits, and thus essentially a reservoir gap. The overall basin configuration, of a large, south-facing horseshoe-shape, also has a major influence on sediment transport trends by forcing transport toward the central part of the basin.

A second order control is provided by dynamic topography of the seafloor, spanning the Albian to Holocene, and driven by mobile salt. The topography built by the salt is responsible for developing both short and long-lived sediment pathways and ‘shadow zones’ where sedimentation is limited. Several key sediment fairway confluences are present in the basin, through which the bulk of sediment gravity flows move. These confluences essentially comprise intraslope-basin channel and lobe complexes, commonly with a very high net-gross and excellent reservoir quality but often lacking a seal.

Finally, numerous faults, unconformities and small-scale topographic elements help control reservoir architecture and distribution. These include the complex topography developed on top of mass-transport deposits, both regional in extent or local to the fairways, and thus provide topographic ‘steering’ of currents and control on resultant reservoir architecture and quality distribution. Sediment waves or depressions and mounds formed or enhanced by both turbidity current overspill from channels, and contour currents are present on much of the slope. Although individually small, these elements comprise an important ‘roughness’ component on the seafloor, and may be instrumental in how sediment becomes distributed along the slope. Although not discretely imaged at depth, their presence can be inferred from seismic character in deep intervals along the slope, and therefore using the recent deposits as an analogue to the deeper sections is essential to understand what impact these features may have had in controlling and modifying reservoir distribution.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013