Seismic Characteristics and Distribution of Hydrothermal Vents in the Rift Section of the Campos Basin, Offshore Brazil

Abstract

Hydrothermal vents are complex pipe-like structures, formed by fracturing, transport and eruption of hydrothermal fluids. This kind of structure is commonly associated with magmatic activity, mainly in the form of sills or similar intrusions. Several studies in sedimentary basins around the world have emphasized the importance of hydrothermal vents as diagnostic markers for magmatic intrusions, which can generate localized heat anomalies that may change the timing and intensity of hydrocarbon generation and promote the circulation of fluids, which may cause significant porosity modification in the reservoirs. Despite the importance of these features for the analysis of petroleum systems, there are few specific studies of hydrothermal vents in the Brazilian South Atlantic margin basins. During this study, several hydrothermal vents and ducts, as well as the intrusive bodies associated with such structures, were mapped in 127 2D seismic lines spaced across an 11,900 km² area located in the central Campos Basin. The seismic attributes that enabled better visualization of these structures were the cosine phase and the instantaneous phase, by highlighting the strong discontinuity of layers and faults. The vents show dome and eye-shaped geometries, and the ducts are most often connected to pre-existing faults. The Campos Basin experienced intense magmatism during the Neocomian, responsible for the generation of tholeiitic basalts floods, diabase intrusions, tuffs, hydrovolcanic breccias, and epiclastic rocks. The hydrothermal vents and their linked intrunsive bodies are distributed along the rift section, which contains the main source rocks of the basin and also encompasses important reservoirs. Hydrothermal activity has promoted enhanced generation and migration of hydrocarbons, as well as of fluids responsible for dissolution and dolomitization in the rift succession, which may have influenced significantly the origin and evolution of the extensive, overlying pre-salt reservoirs.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018