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Abstract

The discovery of the giant Lula Field (Santos Basin, Brazil) has focused exploration on the pre-salt lacustrine carbonate play in both Brazil and Angola. Understanding the main controls on deposition and the link to the unique tectonic setting of the South Atlantic during the Early Cretaceous is paramount in successful exploration. Observations from conjugate regional seismic lines between the Kwanza and South Campos basins define the key megasequences as pre-rift, rift, sag, salt basin, post-salt carbonates and post-salt clastic sediments. The pre-salt stratigraphy can be described by three significant phases. In the first phase, the synrift lakes (Valanginian–Hauterivian), representing the onset of continental break-up and the formation of synrift graben, created several deep basins leading to overfilled freshwater lakes. In the second phase, Sag 1 (Barremian–Aptian), there was widespread subsidence created by syn-kinematic stretching of the continental crust and/or continuous rifting. Lacustrine sediments composed of coarse Pelecypod coquina with moderate faunal diversity are found, suggesting a fresh to brackish, balanced-filled, interconnected lake. In the third phase, Sag 2 (Aptian), there was continuous subsidence and isolation of the lake. Base level falls below sea-level resulted in an under-filled, alkaline and hypersaline lake with widespread microbialite growth. Based on the integration of seismic data, well data, biostratigraphy and tectonic models, a regional predictive model has been developed for reservoirs in phases 2 and 3.

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