--> Abstract: Geology and Petroleum System of the Solimões Basin, Brazil, by J. F. Eiras; #90933 (1998).

Datapages, Inc.Print this page

Abstract: Geology and Petroleum System of the Solimões Basin, Brazil

Eiras, Jaime F. - Petrobras/E&P

The Solimões basin is a wide (450,000 sq km), E-W- trending, Paleozoic intracratonic basin, located between the cratonic areas of both Guyana and Brazilian shields, completely covered by the exuberant Brazilian Amazonian rain forest. It is separated from the Acre basin to the west by the Iquitos arch and from the Amazonas basin to the east by the Purus arch. An internal high (Carauari arch) separates two sub-basins: Jandiatuba to the west and Juruá to the east. These sub-basins are filled up with almost 4,000 m of Phanerozoic rocks. A Proterozoic siliciclastic rift system is deeply buried below the Phanerozoic sequences in the Juruá sub-basin. The Phanerozoic stratigraphic framework is also predominantly siliciclastic in nature, and can be divided into six second-order stratigraphic sequences: Lower Ordovician, Upper Silurian-Lower Devonian, Middle Devonian-Lower Carboniferous, Upper Carboniferous-Lower Permian, Upper Cretaceous, and Tertiary-Quaternary sequences. Paleozoic units do not outcrop at the surface and are often intruded by Triassic (217 Ma) diabase dykes and 3 major regionally extensive sills, which had strongly controlled the thermal evolution of both the source rocks and of the hydrocarbon accumulations.

There are two known petroleum systems in the Solimões basin: Jandiatuba-Juruá (!) and Jandiatuba-Uerê (.) systems. The first one is, by far, the most important. It contains almost all the commercial petroleum accumulations in the basin (99.8%). The essential elements are present and have excellent properties. The source rock is the Frasnian-Famennian marine radioactive black shale of the Late Devonian Jandiatuba Formation, which is up to 40 m in thickness and has more than 4% of total organic carbon. The main reservoir is the Early Pennsylvanian eolian/tidal plain/shallow marine sandstone of the Juruá Formation, in successive beds that attain more than 40 m of thickness (F=18%). Efficient seal is provided by the evaporites found at the base of the Pennsylvanian Carauari Formation. The traps are anticlines located on the upthrown blocks of NE-SW- and NW-SE-trending reverse faults formed during the Mesozoic Juruá compressional event.

The Jandiatuba-Juruá (!) petroleum system is an atypical system, because the low effectiveness of the overburden rock in maturing source rock by burial was compensated for by the thermal effect of diabase sills. Ro is more than 1.00% all over the basin. Trap development started in the Paleozoic; first generation phase by the end of the Paleozoic (transformation rate around 50%); main generation (almost 100% of transformation rate) and expulsion phases in the Triassic, related to the diabase intrusions; followed by secondary migration through Devonian and Carboniferous carrier beds and/or preexisting faults; ending in accumulation of petroleum in older combination traps (broad folds, hinge lines, regional arches, paleohighs, unconformities and pinch-outs). Fundamental re-migration and accumulation of petroleum took place into the younger reverse fault-related traps formed during the Jurassic/Early Cretaceous Juruá tectonic event. Twenty commercial fields (oil/gas/condensate) are known.

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