Print this pageBasement Geology and Structural Modeling of the Santos Basin Pre-Salt, Brazil: "Bottom-Up," Predictive Basin Analysis
Jensen, Luke A.1
Teasdale, 
Jon
P.2
The regional pre-salt geology of the South Atlantic margin basins is challenging to unravel using conventional, “top-down” interpretation, largely due to poor seismic imaging beneath the salt and limited well penetrations to date. We present an alternative “bottom-up” workflow, where basement terranes, inherited structural grains, plate reconstructions, combined seismic- and potential-field interpretation, and 2D and 3D structural restorations illustrate basin kinematic evolution and the timing of key petroleum system elements.
Jurassic-Early Cretaceous, south-to-north propagation of rifting and breakup in the South Atlantic exploited pre-existing Neoproterozoic-Early Paleozoic mobile belts formed during the amalgamation of Gondwana. The contrasting crustal-scale structural framework of each mobile belt is reflected in the related geometry of each overlying basin compartment. In the wide, asymmetric, lower-plate of the Santos basin, analogs that predict high levels of upper crustal extension with sub-horizontal detachments and highly rotated fault blocks are at odds with the conventional notion that the Santos pre-salt is dominated by a simple, upright horst-and-graben rift geometry. Our current model accounts for the required large values of extension with a major, low-angle, detachment-style fault that soles out into an inherited suture zone in the inboard portion of the basin.
Comprehensive imaging, modeling, and interpretation of gravity, magnetic and 2D PSDM seismic data verifies this view of the pre-salt basin geometry in the Santos basin. A set of 2D crustal cross-sections were validated and improved using gravity modeling and structural restoration. Enhancement processing and imaging of magnetic and gravity data were undertaken to reveal map-view basement structures and igneous features. Shell’s proprietary Bathogram™ technology was used to model depth-to-basement from magnetics. Finally, integration of all these outputs generated a sculpted, top-basement surface, which elucidates the structural framework of the basin. 3D structural restorations of the pre- and syn-rift sequences yielded an enhanced understanding of accommodation space development, gross-depositional environment, trap formation, and potential fracture intensity. This new “bottom-up” view of the Santos basin can be used to understand and predict pre-salt paleogeography and petroleum system distribution and timing, and thus generate sweet spots for hydrocarbon exploration.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil