Abstract

The Cabo Frio High corresponds to a regional basement arch located on the continental platform between the Santos and Campos basins. The distal margin of the Cabo Frio Outer High is characterized by gravity and magnetic anomalies suggesting an association with magmatic centers that affected the salt basin. Volcanic rocks are observed both on the proximal margin, where the Cabo Frio Volcanic Complex is marked by several magmatic episodes, and on the distal margin, where the Cabo Frio Outer High is marked by intrusive and extrusive igneous features affecting the pre-salt and post-salt sedimentary successions.

The most important magmatic events in the area are related to (a) the pre-rift phase, with massive lava flows both onshore and offshore of the incipient continental margin; (b) the synrift phase, as indicated by several wells that drilled subaerial basaltic lava flows intercalated with lacustrine sediments; (c) the sag basin and transitional evaporitic post-rift phase, as indicated by sills and laccoliths overlain by salt and also by discordant igneous structures intruded into salt layers; and (d) the post-breakup phase, with major magmatic activity registered in the Upper Cretaceous and in the Paleogene. Volcanic events in the Cabo Frio region are a major factor in basin development and greatly impact the petroleum resources assessment, particularly when igneous rocks intrude into pre-salt source rocks and reservoirs.

The geochemical data from producing fields and exploratory wells in the Cabo Frio region indicate that the main source rock system for the known accumulations are the upper Barremian calcareous black shales, deposited in brackish-to-saline water lacustrine environments from the Coqueiros Formation. In the continental shelf, the oil fields are characterized by intense biodegradation, which has deteriorated the oil quality. Several factors are important elements that control the prospectivity of the Cabo Frio region, such as thermal maturity of the source rocks, reservoir depth, seal effectiveness, magmatic events, and mixing of oils generated from different maturity pulses.