Print this pageStructural Style and Its Role in Diagenesis of the Sergi Formation, Camamu Basin, Brazil
The Camamu Basin, located on the eastern Brazilian continental margin formed as a result of Early Cretaceous rifting between South America and Africa. The basin records a pre-rift Jurassic pulse of subsidence which led to the deposition of a 1200 meter thick sand rich fluvio-aeolian body within an intracratonic sag basin called the Sergi Formation. This unit is the main pre-rift reservoir of the Camamu Basin and is characterized by a heterogeneous suite of reservoir properties.
The pre-rift Sergi Formation overlie remnants of Permian and Carboniferous rocks composed of shales and basalts. The Triassic is totally absent. The pre-Jurassic basement is dominated by a N/S trending hingeline on the western edge of the Camamu Basin with E-W trending faults creating horst and graben features. Near this hingeline of the Camamu Basin, the Sergi Formation exhibits rapid switching from a water rich fluvial environment to a wet aeolian system. The Early Permian Cutler Formation found in Utah, USA provides a good depositional analog for the Sergi Formation along the Camamu Basin margin with many similarities seen in outcrop including near-orthogonal paleocurrent directions between the fluvial and aeolian trends.
The reservoir properties of the Sergi Formation span a wide range from very good to very poor and strongly follow porosity distribution. During the pre-rift/depositional stage the preservation of primary and the development of secondary porosity in these reservoir units are controlled by eodiagenesis and shallow burial mesodiagenesis. At the onset of Early Cretaceous rifting the fault patterns exploited the pre-rift structural fabric resulting in shallow faults and faults that are connected to basement. Diagenesis became significantly influenced by deep-seated fault borne fluids resulting in a complex distribution of reservoir sand quality. The interaction of depositional environment, proximity to deep seated faults and rift aged multi-episode hydrocarbon migration produced a complex diagenetic pattern of porosity preservation resulting in counter-intuitive patterns of oil and gas distribution. These interactions can be used to describe and explain the heterogeneity of the reservoir properties of the Sergi Formation within the western areas of the Camamu Basin.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil