Petroleum geochemical characterization of Albian-Oligocene sequences in the Campos Basin: “Case study: Eastern Marlim oilfield, offshore, Brazil”

Abstract

The current research was performed in the eastern portion of the Marlim oilfield to identify the hydrocarbon-generating potential of the Albian-Oligocene sequences (Macaé Group, Ubatuba and Carapebus formations) in the Campos Basin, Brazil. On the basis of petroleum geochemical proxies, an integrated approach was developed using source rock characterizations to establish the distribution of source rock properties, such as organic matter content, hydrocarbon-generating potential, thermal maturity and stratigraphic thickness. The outcomes of a comprehensive petroleum geochemical characterization were integrated with cuttings and core sample descriptions, biostratigraphic controls, well log analyses and 2-D/3-D seismic interpretations. Our results reveal that for the Albian-Oligocene deposits, the key geochemical properties required to develop hydrocarbon source kitchens converge in specific locations, demonstrating a variable hydrocarbon potential ranging from poor to excellent and suggesting the existence of local generation pods in the central and principally northern portions of the research area. The accumulation and preservation of the organic matter were influenced by the paleo-topography and tectonic controls, and the lowest concentrations of organic carbon were attributed to significant siliciclastic dilution taking place mostly toward the middle and southern portions of the Eastern Marlim oilfield. Lateral variations in both the lithofacies and organic facies are the main conditions controlling the behavior of the petroleum potential in the investigated sediments. Our results indicate that the Macaé Group has sufficient source-rock potential, maturation patterns, and hydrocarbon-generating potential to be considered as an active source rock in the Eastern Marlim oilfield, where the petroleum geochemical properties converge and are adequate to generate hydrocarbon compounds. In addition, the Ubatuba and Carapebus formations are also likely to generate oil and/or gas, but due to their relatively low maturity, it is difficult to establish that these rocks can be active source rocks in the study area.