Facies and paleoenvironments of the Coqueiros Formation (Lower Cretaceous, Campos Basin): A high frequency stratigraphic model to support pre-salt 'coquinas' reservoir development in the Brazilian continental margin

摘要

Lacustrine carbonatic deposits are generally little studied, partly because of their lesser representativity in the global geological record, as well as the smaller amount of oil reservoirs associated with these types of rock. But the Cretaceous (Aptian Barremian) lacustrine carbonates recorded on the eastern Brazilian coast from Santos to Sergipe-Alagoas basins, attributed to the rift and post-rift phases that preceded the opening of the Atlantic Ocean, has been registering important hydrocarbon discoveries since the 1970s to the present day. This study aimed to expand the knowledge of these deposits by analysing the facies and associations, defining sequences according to the current understanding of the sequence stratigraphy concepts. Rock samples were described associated with core and seismic profile data from the Badejo, Linguado, Pampo and Trilha fields in the Campos Basin. As the main lithology sampled was bioclastic (bivalves) carbonates. Were defined fifteen facies according to sedimentological criteria associated to taphonomy concepts and also grouped in four associations interpreted according to the hydrodynamic gradient of a wave-dominated shelf. This enabled the definition of high and medium frequency sequences, which aided the description of three internal sequences in the interval known as Lower Coquina. This methodology can be used to interpret facies spatial distribution and serves as an analogue for cycles definition in similar depositional systems.