Palaeotopography Restoration and Its Importance to Predict Turbidite Reservoirs Distribution Influenced By Salt Movements
The relief of the ocean floor partly controls the distribution of the turbiditic systems, the channel pathways being guided by topographic highs while lobes are ponded into sub-basins. The topography also changes through time as the margin is deformed, modifying the depocenters at the regional scale, specially when salt is implied. At the reservoir scale, the dynamic of the gravity flows is also assumed to be strongly influenced by the effect of the topography.
The
aims of this work are to present (i) the methodology used to restore through different times the structural topographies influenced by salt movements and (ii) the results indicating how these paleotopographic surfaces affected the sedimentation.
The database comes from the Upper Cretaceous turbidite reservoirs in a central region of the Brazilian offshore Campos basin, and includes 3D seismic
and well information. The Campos basin is a typical passive margin basin on which tectonics is partly controlled by halokinesis.
The methodology included, at semi-regional scale, stratigraphic and structural interpretation, 3D surface modeling
and structural restorations, together with reservoir interpretation. Six
seismic
-lithologic horizons were mapped, from the Aptian salt to the Miocene, including a complex fault pattern. The 3D
modeling
comprised fine adjustments and contact building between horizons and faults. Individual surface restorations performed in all horizons improved the structural coherence of the interpretation and quality of the unfolding-unfaulting. Multi-surface restorations
were then carried on in order to determine the horizon paleotopographies. The resulted geologic 3D model included the detailed reservoir sequences, mapped between two regional horizons.
The result analyses indicate that the halokinesis-related growth faults regulated the distribution of the basal reservoirs in a complex manner. Moreover, at the top of the Albian carbonates and cross-cutting the main trend of the structures, a canyon feature was identified; it constitutes, in addition with the tectonic topography, the main controls on the upper reservoirs geometry.
We are currently proceeding to process-based simulation of turbiditic flow using the restored surfaces as topographic constraints to guide the flow, with the objective to predict the facies distributions. By this way, the understanding on the local interactions between topography and sedimentation processes is expected to be improved.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil