The shallow hydrocarbon-derived structures of Brazilian Equatorial Margin, a seismic approach on the offshore Barreirinhas Basin
Brazilian equatorial margin; conventional seismic; gas chimney; mud diapir; pockmark
Abstract (english):
The Brazilian equatorial margin (BEM) is an oblique-transform segment with counterparts in the Gulf of Guinea on West Africa. Both margins are inherited from the Pangea breakup. These areas have been studied as new exploratory frontiers and recently gained attention due to petroleum systems found in deep and ultra-deep waters. However, there is little research about the several basins of the Equatorial Atlantic. The Barreirinhas Basin, located at the central portion of the BEM, is a strike-slip basin highly controlled by the transtensional and transpressional tectonic activity of the Romanche Fracture Zone (RFZ). The objectives of this scientific study are to contribute to geological comprehension about Barreirinhas Basin and identify shallow hydrocarbon-derived structures. Conventional seismic reflection in post-stack time migration was implemented; seismic attributes were applied to enhance seismic interpretation. The main recognized shallow strata features are gas chimneys, pockmarks, bottom simulating reflectors (BSR), hydrocarbon-related diagenetic zones (HRDZ), mud diapirs and mud volcanoes. Many of these structures are seen together, with correlated genesis, and acting as indicative of hydrocarbon seepage. Fault-related gas chimneys are abundant near to the shelf break, carrying shallow source of gas to the surface and making pockmarks; deep-rooted chimneys and pockmarks are present on thrusts and folds at transition lower slope-abyssal plain, on western basin; the continental slope has occurrences of BSRs, gas chimneys, pockmarks. In the west, some HRDZs were identified. All these structures are responsible for hydrocarbon migration, mainly in the presence of canyons, deep channels and turbidites; several mud diapirs and mud volcanoes are found on basin depocenter, indicating high sedimentation rates and active hydrocarbon generation.