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Petroleum Geology of the Amazonas Basin, Brazil: Modeling of Hydrocarbon Generation and Migration

By
F.G. Gonzaga
F.G. Gonzaga
Petrobrás E&P Rio de Janeiro, Brazil
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F.T.T. Gonç;alves
F.T.T. Gonç;alves
Petrobrás CENPES Rio de Janeiro, Brazil
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L.F.C. Coutinho
L.F.C. Coutinho
Petrobrás E&P Salvador, Brazil
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Published:
January 01, 2000

Abstract

The Amazonas Basin is a 500,000-km2 intracratonic basin in northern Brazil. The ~6000-m lithologic section encloses mainly Paleozoic sedimentary rocks intruded by Triassic–Jurassic diabase dikes and sills, and subsequently buried by Cretaceous–Tertiary rocks. Geochemical and geologic data point to the Upper Devonian marine black shales from Barreirinha Formation as the main hydrocarbon source rocks.

Data from 11 selected wells were used to perform thermo-mechanical modeling. Backstripping and stratigraphic analyses indicate four extensional events: Ordovician–Early Devonian, Devonian–Early Carboniferous, Middle Carboniferous–Permian, and Cretaceous–Tertiary The tectonic subsidence curve of each well was compared to theoretical subsidence curves to define the extensional factors and determine the heat flow history. The integration of 1-D basin modeling with geologic and geochemical data suggests that the Barreirinha Formation source rock started to generate petroleum during the Late Carboniferous. Modeling of primary migration indicates that the main phase of oil expulsion began when the source rock attained a transformation ratio of ~50% and a maturation level of 0.80% Ro. The main phase of petroleum generation and expulsion occurred from Late Carboniferous to Permian time and was completed by the Early Triassic. Any later tectonic event remobilized those hydrocarbons previously trapped.

Preliminary volumetric calculations indicate that up to 1 trillion bbl of oil equivalent were expelled from the source rock. Because of the long distances of both vertical and horizontal migration, it is believed that an important amount of the expelled hydrocarbon was dispersed along migration pathways. A significant part could also have been remobilized and lost during Cretaceous uplift of the basin margins.

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Contents

AAPG Memoir

Petroleum Systems of South Atlantic Margins

Marcio Rocha Mello
Marcio Rocha Mello
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Barry J. Katz
Barry J. Katz
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American Association of Petroleum Geologists
Volume
73
ISBN electronic:
9781629810706
Publication date:
January 01, 2000

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