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Pre-Salt Microbial Carbonate Reservoirs of the Santos Basin, Offshore Brazil

Wright, Paul V.1; Racey, Andrew 1
1 Advance Team, BG Group, Reading, United Kingdom.

The major discoveries of hydrocarbons in the Pre-Salt of the Santos Basin, offshore Brazil, are hosted largely in non-marine microbial carbonates. Reservoir quality is strongly facies controlled. A facies model is presented to explain the origins and relationships of the three main facies types: microbial shrub biostromes, coarse spherulitic limestones and laminated (locally varved) carbonate silts to mudstones. Multi-phase diagenesis has overprinted the facies but late stage corrosion has enhanced remnant primary porosity. A challenge in predicting reservoir distribution and quality is to find an analogue for what appears to have been a very unusual deposystem. A series of candidate models has been developed using modern day and ancient non-marine microbial carbonates, and these models are compared with the Pre-Salt data sets including seismic features to distill a model. Any model also has to explain the apparent common occurrence of unusual vertebrate material.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009