Print this pageAbstract: Foz Do Amazonas Basin Hydrocarbon System
Silva, Sérgio Rogério Pereira da; Maciel, Rosangela Ramos - Petrobras/E&P
The Foz do Amazonas basin is located
on the northwestern part of the Brazilian equatorial continental margin.
The Cenozoic interval is characterized by a thick Paleocene-Miocene carbonate
platform on the present shelf area and by a thick prograding prism of mainly
Upper Miocene-Recent siliciclastic sediments on the slope and deep basin.
The first drift 
sequence
of the basin corresponds to an Upper Cretaceous
siliciclastic succession, which overlies rift sediments of Albian to early
Cenomanian age or even the Precambrian basement. Towards the slope and
deep basin, Cenozoic gravitational tectonics dominates the regional geological
framework. There are several structural and stratigraphic traps distributed
throughout the basin. This work aims at discussing the application of the
petroleum system concept in the assessment of exploratory risk of the Foz
do Amazonas basin.
A multidisciplinary approach was developed to
distinguish the main petroleum systems in this basin. The analysis of the
main potential source rocks in this basin has shown three intervals (marine
rift, Cenomanian-Turonian sequence and lower Tertiary). The regional structural
and stratigraphic investigation on seismic reflection profiles (Fig. 1)
integrated with well data (biostratigraphy, electrical profiles and cores)
shows the relationship among the structures, sedimentology and stratigraphy
of the potential reservoirs (Tertiary carbonates, siliciclastic of Cretaceous
and Plio-pleistocene) and source rocks. The analysis of growth curves of
deep faults in this basin shows periods of fault activity and rapid sedimentation
in upper Cretaceous and upper Tertiary. These fault zones can act as conduit
to secondary migration and improve vertical migration pathways in different
stages of the geological history of the basin. The geohistory analysis
produced sediment accumulation rates and curves for subsidence through
time (Fig. 2). The effect of the sedimentary load in the subsidence curve
was evaluated and removed using a backstripping technique. Crustal profiles
were constructed, based on deep seismic profiles constrained by gravity
modeling (Fig. 1). Using the uniform extension model, it was also possible
to construct maps of crustal stretching factors based on independent methods
described above. The thermal conductivity of the matrix of rocks was estimated
based on lithology type. Temperature (depth) was predicted by regional
seismic stratigraphic analysis (depositional style). The thermal maturity
of the source rock was obtained by heat flow analysis, at several evolutional
stages, using the Lopatin method. After that, the comparison of the distribution
of gas and oil in the main reservoir intervals with source rock maturation
maps shows a good correlation.
Thus, it was possible to make a regional integration
of all available data on reservoirs, traps, seals and the timing of generation
and migration, resulting in the selection of the main plays. Lastly, the
hydrocarbon potential and the exploratory risk of the Foz do Amazonas were
evaluated in the framework
of basin evolution.
AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil