Print this pageA Step Back: Integrating Tectonics and Geochemistry to Evaluate Future Pre-Salt Hydrocarbon Systems Along Offshore Brazil- Predicting the Future?
Last year, 2008 proved hugely successful for the drilling of pre-salt reservoirs, with three of the largest oil discoveries being discovered in the Santos Basin. In addition, further pre-salt discovery successes in Campos and Espirito Santo illustrate the lateral continuation of this petroleum system northward.
However, despite these drilling successes, Santos, Campos and Espirito Santo still remain underexplored for pre-salt targets. The aim of this poster is to illustrate that offshore Brazilian basins contain all of the necessary petroleum system elements considered essential for the existence of significant oil and gas accumulations.
Palaeogeographic reconstructions of the South Atlantic Salt Province illustrate rifting during Early Cretaceous created a series of half-grabens and fresh water/saline lakes with accumulation of fluvial clastics, lacustrine shales and carbonate sediments comprising excellent source and reservoir potential.
Onset of thermal subsidence and marine incursion during the Aptian created an elongate gulf and evaporitic basin. The Aptian salt domain extends from NW-SW trending Torres Arch, in the south to the east-west trending Pernambuco Shear System, in the north. The salt basin varies from 500km in width from the Santos Hinge line to the frontal edge of the salt, whilst in Espirito Santo the salt basin narrows to 150km. Salt thickness is also highly variable from 200m in proximal western margin to 2000m in the depocentre e.g. at Tupi field, to less than 200m at Jubarte field in Campos. In Sergipe-Alagoas there is a lack of significant salt deformation structures, salt here is generally less than 100m.
The varying thickness and distribution of salt in the offshore Brazilian basins is highly significant due to its high thermal conductivity, slowing thermal maturation. Geochemical modelling illustrates the syn-rift lacustrine source rocks extensively reached peak oil maturity later than expected considering their depth of burial. The thermal and elastic properties of the salt also help preserve liquid hydrocarbons in the deep pre-salt reservoirs as well as preserving porosity of the deep reservoirs.
This poster shows that by stepping back to understand the regional tectonic development a detailed appreciation of the stratigraphy, source, reservoir and thermal maturation can be achieved to provide further insights into predicting possible future areas for where new pre-salt petroleum systems may be discovered.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil