Shallow Strata Expressions of Leakage and Seepage Structures Associated With Hydrocarbon Migration: a Seismic Analysis on Offshore Barreirinhas Basin, Brazilian Equatorial Margin

Abstract The Brazilian Equatorial Margin (BEM) is an oblique-transform segment with counterparts in the Gulf of Guinea on the West Africa Margin, inherited from the Pangea breakup and Atlantic Ocean opening. These areas are exploratory frontiers where recently petroleum systems were found in deep- and ultra-deep waters. The strike-slip Barreirinhas Basin, at the central portion of the BEM, is conjugated with the oil and gas producers Ivory Coast and Tano basins, whereas the Barreirinhas Basin has currently no relevant discovered petroleum reservoirs. This present study aimed to identify and map distribution patterns of leakage and seepage features in shallow strata, indicating potential hydrocarbon migration and accumulation along the offshore Barreirinhas Basin. The investigation used conventional 2D seismic reflection data with additional application of seismic attributes, including RMS amplitude, instantaneous amplitude, instantaneous frequency, and chaos. Diverse hydrocarbon leakage and seepage structures were identified, including faults, gas chimneys, pockmarks, hydrocarbon-derived diagenetic zones, bottom simulating reflectors, and mounds. Regional morphological and stratigraphic structures constrain the zones of fluid leakage and seepage, which indicate potential hydrocarbon migration pathways. In the eastern lower continental slope and continental rise, regional faults and gas chimneys control seep formation. On the central to northern sectors of the continental rise and abyssal plain, several deep-water mounds are linked by large gas chimneys and faults. There are gravitational gliding systems on the western and central portions of the basin, where the extensional domain is characterized by listric faults, negative flower structures, and gas chimneys that produce cold seeps on the outer shelf and upper slope. These structural controls are related to the compressional domain of the lower continental slope and continental rise, where the decollement zone and a series of faults and folds are correlated to pockmarks and deep-water mounds. Near the western compressional domain, igneous intrusions control the development of leaking faults, gas chimneys, bright spots, and pockmarks. These hydrocarbon-derived structures, seeps, and pathways of fluid migration in deep-water indicate potential petroleum systems in the Albian to Turonian-Oligocene tectono-sedimentary sequences in the central sector of the Brazilian Equatorial Margin.