--> Seismic Characterization of Early Cretaceous Fluvial-Deltaic Sandstones, Middle to Late Cretaceous Turbidites and Late Cretaceous Channelized Features in the Foz do Amazonas Basin, Northern Brazil

AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Seismic Characterization of Early Cretaceous Fluvial-Deltaic Sandstones, Middle to Late Cretaceous Turbidites and Late Cretaceous Channelized Features in the Foz do Amazonas Basin, Northern Brazil

Abstract

The Foz do Amazonas basin, located on the northwest part of the Brazilian equatorial continental margin, covers an area of about 360,000 km2. The basin occurs in an area where major discoveries offshore the coast of Brazil have been found in carbonate-filled, sag basins with potential for exploration opportunities in siliciclastic settings. The proximity of the Foz do Amazonas basin to the 2011 Zaedyus discovery in French Guiana indicates the presence of a working petroleum system with proven source rocks of both Aptian and Cenomanian-Turonian age (Limoerio Formation). The steep shelf edge of Foz do Amazonas basin has been affected by gravitational tectonics characterized by normal faulting along the shelf margin, and convergence at the base of the slope that is spatially associated with the St. Paul Fracture Zone. In addition, the steep shelf margin region has undergone significant modification from mass wasting events and debris flows due to periodical failure of the unstable slope. Based on seismic facies analysis from 21,369 km of 2D seismic data, we identified Early Cretaceous and Late Cretaceous to Early Paleocene reservoir sands and trapping mechanisms – involving the Cassipore and Limoeiro Formations, respectively. The continental shelf, slope, and deep marine deposits constitute a play model which has not been drilled, and has been successful in the conjugate margin of Sierra Leona and Liberia. In order to evaluate the prospectivity of Cretaceous stratigraphic features and their distribution along the study area, we conducted seismic interpretation, seismic facies and attribute analysis, along with seismic geomorphology to identify several stratigraphic traps, that include: 1) a mid-Cretaceous section of shallow water, lacustrine and fluvial-deltaic depositional systems that filled Aptian and Albian graben systems during the syn-rift stage of the basin development (Cassipore Fm.), 2) Middle to Late Cretaceous mass transport complexes (Upper Cassipore Fm.) and Turonian turbidite fans (Lower Limoeiro Fm.) along the slope section, 3) Late Cretaceous to Early Paleocene shelf sands system that fed deep marine turbidites fans (Limoeiro Fm.), and 4) Younger, Late Cretaceous to Paleocene (?) mud and sand-filled channelized features (Limoeiro Fm.) interpreted as reservoir-seal pairs with updip seal being the highest risk factor.