Campos and Santos Basins: 40 Years of Reservoir Characterization and Management of Shallow- to Ultra-Deep Water, Post- and Pre-Salt Reservoirs - Historical Overview and Future Challenges

Abstract

Petrobras found almost 100 hydrocarbon accumulations in the Campos and Santos basins, between 50 and 300 km off the Brazilian coast (under water depths from 80 to 2,400 m), which produce from very different types of reservoirs, including mostly (1) pre-salt coquinas and microbialites, (2) post-salt calcarenites, and (3) post-salt siliciclastic turbidites. These different types of reservoirs, containing also different types of hydrocarbons and contaminants provided many challenges for their production development, related to distinct tools and workflows for reservoir (static/dynamic) characterization and management, seismic reservoir characterization and monitoring, recovery methods (water injection, WAG, etc.), well spacing, well types and geometries, subsea systems, and processing capacity of production units. Since the first oil and gas discoveries in the Campos (1974) and Santos (1979) basins, Petrobras continuously moved to aggressive exploration and production from shallow- to deep- and ultra-deep waters. During the last 40 years, the activities of reservoir characterization and management have also continuously evolved. Four major phases can be depicted: (1) shallow water fields developed with a large number of vertical or deviated wells (e.g. Namorado, and Pampo, Campos Basin); (2) deep water fields, still developed with a large number of wells, but now combining vertical/deviated and horizontal wells (e.g. Marlim and Albacora, Campos Basin); (3) deep to ultra-deep water, post-salt fields, containing light to heavy oil (13-31 °API) in siliciclastic turbidites and carbonates, developed with a relatively small number of mostly horizontal wells (e.g. Marlim Sul, and Barracuda, Campos Basin); (4) ultra-deep water, pre-salt fields with very thick (up to 400-500 m), light oil (27-30 °API) carbonate reservoirs, developed with largely-spaced vertical and deviated wells (e.g. Lula, and Buzios, Santos Basin).

Impact of stress regime change on the permeability of a naturally fractured carbonate buildup (Latemar, The Dolomites, Northern Italy)

“…Further, fracture networks, including intensely fractured zones, are believed to significantly influence the effective permeability and fluid flow patterns in a naturally fractured reservoir, particularly in tight carbonate reservoirs. These network areas show high porosities and permeabilities relative to the surrounding host rock (Bruhn et al, 2017;Matthäi, 2003). It is a widely held view that the extent to which the fracture networks impact flow lies in the fracture's structural arrangement and geometry, such as fracture orientations, spacing, and length (Bisdom et al, 2016;Hardebol et al, 2015;Olson, 2003;Scholz, 2010).…”

Hydrocarbon Generation and Migration From Barremian – Aptian Source Rocks, Northern Orange Basin, Offshore Western South Africa: A 3d Numerical Modelling Study

“…Cenozoic turbidites also probably occur in the Orange Basin together with widespread Late Cretaceous slumps, gravity flows and mass transport deposits (de Vera et al, 2010, Scarselli et al, 2016. Cenozoic turbidites have also been reported in the conjugate margins offshore Uruguay and in the Santos Basin (Rodriguez et al, 2019;Bruhn et al, 2017). Exploration of the turbidites play offshore Uruguay has not been successful largely due to lack of charge access, explained by the distance of the reservoirs from a source rock kitchen and by the absence of faults as migration pathways (Rodriguez, et al, 2019).…”

“…Uplift and erosion of the Southern Africa continental hinterland during the Cenomanian (Braun et al, 2014) may have resulted in elevated sediment transport to the coastal basins, causing overall progradation of the Orange Basin fill (Dingle et al, 1983). The highest average global climatic temperatures during the Cretaceous occurred in the Cenomanian (Caldeira et al, 1991), and the elevated transports of sediments to the coastal basins may have been aided by high rates of denudation in the hinterland. Significant thermal effects within the sedimentary succession due to high sedimentation rates (Lucazeau and Le Douaran, 1985) coupled with a basal heat pulse are evidenced by the modelled VR values which are less than the measured VR in well AO-1 in the north of the study area (red circle in Fig.…”

“…Similar depositional processes occurred in the Orange and Santos Basins until the late Aptian, after which the development of salt structures in the Santos Basin controlled subsequent sediment deposition and hydrocarbon accumulation/ migration. Hydrocarbon accumulations in the basin mainly occur in carbonates in the pre-salt succession but also occur in post-salt calcarenites and siliciclastic turbidites (Bruhn et al, 2017). In the Orange Basin offshore South Africa by contrast, the main gas discovery occurs within an Albian siliciclastic reservoir, with additional potential reservoirs in the Cenomanian.…”

Neural network unsupervised classification as an advanced presalt reservoir characterization technique - a Buzios Field case study

“…The pre-salt reservoirs in the Santos Basin are one of the most challenging targets for the exploration and production of oil and gas, due to their geological heterogeneity and anisotropy requiring the deep understanding of depositional and post-depositional processes coupled with advanced reservoir characterization techniques for precise positioning of wells (Bruhn et al, 2017).…”