Oil and Gas Potential of the Amazon Paleozoic Basins

Abstract

The Paleozoic basins, covering an area of about 800,000 km/sup 2/ (309,000 mi/sup 2/) in the Amazon region, are elongate symmetrical intracratonic synclines filled with as much as 4000 m (13,000 ft) of sediments, separated by basement uplifts or major arches and located in continental interior areas (as are the United State Illinois, Michigan, and Williston basins). Tectonics affected differentially these basins during the Triassic Jurassic and Early Cretaceous, associated with widespread basic volcanism. Adjacent to those faults and extending for over 500 km (310 mi), large natural gas accumulations occur in several domal features. Sandstones of the Permian Monte Alegre Formation, sealed by evaporite strata, are the main reservoir rock. Geologic estimates of natural gas resources are presently rated at 120 billion m/sup 3/ (4.237 tcf) and exploration follows the productive trend toward the west-southwest. Potential reservoir rocks in Middle and Lower Amazon basis are Permian Monte Alegre and Devonian Oriximina sandstones. Major source rocks in all three basins are Devonian Barreirinha black, shales. Forecasts for the major exploratory trends in the Upper Amazon indicate a good possibility of extending the already discovered natural gas province. In the Lower Amazon basin, further exploration will consist in drilling well-defined structuralmore » features identified for the first time by seismic methods, with a possibility of discovering another gas province. Prospects in the Middle Amazon basin are for both oil and gas, but the main problem is identification of adequate structures, as well as stratigraphic traps.« less