--> Abstract: Petroleum System of the Camamu Almada Basin: A Basin Modeling Approach, by F. T. T. Gonçalves, R. P. Bedregal, L. F. C. Coutinho, and M. R. Mello; #90933 (1998).

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Abstract: Petroleum System of the Camamu Almada Basin: A Basin Modeling Approach

Gonçalves, F. T. T.; Bedregal, R. P.; Coutinho, L. F. C.; Mello, M. R. - Petrobras/ Cenpes/E&P

In previous studies, the integration of geochemical, geological, geophysical and biostratigraphic data, allowed the characterization of the Morro do Barro (!) petroleum system in the Camamu-Almada basin, located in northeastern Brazil (Fig. 1). Morro do Barro Formation source rocks comprises lacustrine fresh to brackish water black shales of lowermost Neocomian age. Such shales are characterized by a thick succession (up to 800 meters in thickness) with total organic carbon (TOC) ranging from 2 to 10%, and hydrogen indices HI values around 600-800 mgHC/gTOC. Hydrocarbon accumulations in the basin occur in structural traps along the Pre- and Synrift sedimentary section. In the former case, oil is trapped in the eolian and fluvial sandstone reservoirs of the Sergi Formation (Jurassic), whereas the other petroleum is trapped in the Morro do Barro Formation turbidite sandstones.

In this study, 1-D and 2-D basin modeling were performed in order to improve the comprehension of the interplay between the elements and processes of the petroleum system and to help in the prediction of hydrocarbon occurrence and characteristics. The 1-D basin modeling study comprised backstripping analysis, thermo-mechanical modeling, thermal and kinetic simulation of 12 wells and 29 pseudo-wells. The results indicate that most of the oil was generated by the end of the rift phase (Barremian to Aptian). A set of maps of kerogen transformation ratio at different ages allowed the characterization of the oil-kitchen evolution through time and space in the studied area.

The 2-D generation and migration modeling was performed in a 30km-long W-E cross-section (Fig. 2). The results indicate that a hydrostatic pressure profile prevailed throughout basin evolution, even during periods of high sedimentation rates. Kinetic modeling of Morro do Barro source rocks shows that most of the oil was generated during the rift phase. Present kerogen transformation ratios range from 10-20% nearby the continent (W) to 100% in the deeper area (E). The presence of a thick section of low-permeability shales above the source rocks favored the downward migration of petroleum to the sandstones of the Sergi Formation. Petroleum migration through normal faults which juxtaposed source rocks of the Morro do Barro Formation to sandstones of the Sergi sandstones played also a major role in the filling of these carrier-beds. Secondary migration extended considerably into the post-rift phase and allowed petroleum to reach the shallow pre-rift structural traps located in the W of the section. Gas formation started in the late stages of the rift formation and continued along the post-rift evolution of the basin.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil