Reservoir Distribution in a Ponded, Mass-Transport Dominated Channel-Lobe Complex, Espiacute;rito Santo Basin, Offshore Brazil
Janocko, Michal1; Warchol, Michal; Dykstra, Mason; Husmo, Tore; Bakke, Kristina; and Hadler-Jacobsen, Frode
Frequency decomposition of 3D seismic-reflection data from the upper slope of Espiacute;rito Santo Basin, offshore Brazil is used to study the development and reservoir distribution of a Neogene deep-water channel-lobe complex. The complex is confined to an elongate salt-withdrawal basin and consists of three channel-lobe systems with two separate entry points. The distal part of the complex also interfingers with the margin of a large mass-transport fairway which is diverted into the minibasin from yet another direction. The lobe deposits are typically fed by a tributary network of channels and sheet-like mass-transport deposits (MTDs), and comprise intercalated turbidites with MTDs at a range of scales. Turbidite deposits are recognized on seismic frequency color-blends as channel- and lobe-like features with a consistent texture, whereas MTDs typically show a blocky pattern and geometries resembling frondescent splays, straight chutes, tabular sheets and tongue-shaped mounds. Besides the interplay of turbidity currents and mass-wasting processes the formation of the lobe complex seems to have been further complicated by syn-sedimentary halokinesis, salt-induced faulting, local mass-wasting of the minibasin margins and coeval deposition of the adjacent MTD fairway. On the basis of previous studies, turbidites are inferred to be sand-prone and represent reservoir facies. MTDs are assumed to be mud-prone and correspond to potential flow-barriers.
The thickness of most turbidite and MTD units is below the resolution of full-frequency seismic data. However, frequency color-blend maps allow the average frequencies across the studied area to be measured and the relative thickness of individual elements to be determined. Salt diapirism, faulting and the emplacement of MTDs resulted in a varied but predictable thickness distribution of the turbidite units. Turbiditic channels accentuate the rugged topography of the underlying MTDs by invasive erosion, whereas splay deposits tend to heal the pre-existing relief. Turbidites display the greatest thicknesses at channel-splay transitions, upslope and along the edges of adjacent lobe deposits and in some cases at the lobe fringes.
The work identifies several reservoir-trap combinations that can be used as direct analogues for some Paleogene prospects in the studied basin, as well as hydrocarbon plays in other parts of the world where reservoir levels consist of intercalated mass-transport and turbidite deposits.
AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013