3D-Petroleum System Modeling of the Deep-Water Pernambuco-Paraíba Basin, Brazil
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BPS recently performed, in association with TGS/Spectrum, an entirely new 3D-Petroleum Systems study of the deep-water area of the Pernambuco-Paraíba Basin. Petroleum Systems Modeling (PSM) is a technique for three-dimensional visualization and mathematical simulation of the layers that can generate and accumulate hydrocarbons in the subsurface, as well as the movement of fluids inside the rock porosity.
The study utilized a detailed structural and stratigraphic framework, or geometric skeleton, of the geologic layers and faults inside the basin. It interpreted Spectrum’s 5,498 linear kms of excellent-quality, long-offset, 2D-seismic data acquired in a 10 km X 10 km grid. It also includes a comprehensive oil-slick satellite survey to characterize the presence of oil floating on the water, as well as a previous oil-seep piston core study that acquired samples of the seafloor sediment (Figures 1 and 2).
Using Radarsat and Sentinel satellite and piston core technologies, oil slick and oil seep anomalies were identified all over the basin. Advanced Geochemistry Analysis (AGT), representing the use of cutting-edge techniques for the study of the processes that control the composition and distribution of chemical compounds and isotopes in geologic environments, was performed on the oil seeps, showing biomarker data (a measurable indicator of ancient biological processes) that is compatible with the oils that were generated by the Aptian lacustrine-anoxic sediments of the Cabo Formation, which is equivalent to the Aptian Muribeca and Alagamar formations of the Sergipe-Alagoas and Potiguar basins, respectively. The lacustrine-anoxic environments imply the paucity of oxygen in the water layer and organic matter can be preserved in the bottom waters, which is in line with the fact that the Albian-Cenomanian marine anoxic shale-rich sediments present in the basin are considered to be immature (did not get hot enough or enough pressure to generate hydrocarbons) and therefore cannot be considered source rock. However, for the deeper sediments of the Aptian, the ideal temperature and pressure to generate hydrocarbons were confirmed via PSM.
The integration of the results allowed for the identification, with a high level of confidence, of the key petroleum system elements present in the basin. The mapped Lower Cretaceous rift systems, representing ancient lake or rift systems from the Cretaceous Age (from 66 to 100 million years ago), showed that the rifting processes in the Pernambuco-Paraiba Basin created a complex structural framework, or an intricate disposition of the layers and faults in the subsurface, inside sunken areas where sediments rich in organic matter were deposited and preserved due to euxinic bottom-water conditions (absence of oxygen at bottom of the water body), allowing the preservation of organic matter without destruction via oxidation.
These deep depopods, or expressive depressions in the earth’s crust, are confirmed by the seismic data, showing that they buried deep enough to attain peak to late-peak oil window stage generation. The traps or elements that hold and inhibit the escape of the hydrocarbons from the reservoir were observed in the Aptian syn-rift sediments, representing structural and stratigraphic traps that are related to fault-block rotation, basin tilting, gravity sliding, and channel/canyon cuts. The main potential reservoirs are the syn-rift lacustrine fluvio-deltaic sediments of the Cabo Formation that are widespread across the basin. These sediments were deposited by rivers or areas where the rivers flow into the water body, named deltas in a lake system.
The interpreted Aptian source rocks can be regionally traced and correlated through the seismic data with the oil-prone source rocks responsible for the generation of most of the oils discovered to date in its neighboring Sergipe/Alagoas and Potiguar basins. Therefore, the Pernambuco-Paraíba Basin’s potential for bearing significant light oil discoveries cannot be deemed to be lower than those encountered in those basins.
The results from integrating and interpretation of all the data, together with 3D-basin-modeling, show that the Pernambuco/Paraiba Basin has a rich and active lacustrine petroleum system with excellent potential for the presence of source and reservoir rocks in trapping conditions in its late-rift and post-rift sequences. The 3D basin modeling outcomes confirmed favorable conditions for migration of hydrocarbons that have the potential to charge traps of considerable size, which may represent a great opportunity for discoveries of light oil accumulations once a more comprehensive exploration program, including the drilling of the first wells, is run in this promising frontier basin.
Figure 1. Location map of the Pernambuco-Paraíba Basin showing the new TGS/Spectrum seismic survey and its location southeast of the Potiguar Basin and northeast of the Sergipe-Alagoas Basin. The green dots are oil slicks, identified by Radarsat satellite detection technology and the red dots are Piston Core samples that were taken from the seabed and showed the presence of Aptian lacustrine oil and gas seeps.
Figure 2. An example of a TGS/ Spectrum high-quality seismic line used in this project (Kirchhoff PSTM stacks). As you can see, it clearly shows the presence of two thick Syn-Rift sedimentary layers and a thin post-rift sequence. This is an indication that the basin remained starved for a long period of time.