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Relating Petroleum System and Play Development to Basin Evolution: Brazilian South Atlantic Margin*

 

Suzanne Beglinger1, Harry Doust1, and Sierd Cloetingh1

 

Search and Discovery Article #40520 (2010)

Posted March 25, 2010

 

*Adapted from extended abstract prepared for oral presentation at AAPG International Conference and Exhibition, Rio de Janeiro, Brazil, November 15-18, 2009. Please refer to closely related article by Susanne Beglinger et al., 2009, Relating Petroleum System and Play Development to Basin Evolution: West African South Atlantic Basins, Search and Discovery article #40440 (2009).

 

1 Tectonics, Faculty of Earth & Life Sciences, VU University, Amsterdam, Netherlands ([email protected])

 

Abstract

Sedimentary basins can be classified according to their structural genesis and evolutionary history and the latter can be linked to petroleum system and play development. The Brazilian marginal basins, comprising the Sergipe-Alagoas, Jacuipe, Almada-Camamu, Jequitinhonha, Cumuruxatiba, Espirito Santo, Campos and Santos basins, have experienced a similar tectonic and sedimentary basin evolution. Four basin cycles have been distinguished (pre-rift, syn-rift, transitional and post-rift), of which three are associated with at least one type of source rock giving rise to a specific type of petroleum system (PST).

The lacustrine syn-rift PST is regionally extensive and the most productive. Despite the widespread distribution of transitional and post-rift source rocks, the restricted hypersaline marine transitional PST and shallow and deep marine post-rift PSTs have only been proven active locally, due to the relatively low maturity of these source rocks. Play development is closely related to basin tectonic and sedimentary evolution: syn-rift plays are associated with lacustrine/fluvial facies in combination with trap geometries related to graben development. Post-rift plays include deltaic and shallow to deep marine clastic and carbonate facies in combination with traps which formed due to halokinesis.

The number and variety of plays increase with basin evolution, as tectonic and sedimentary patterns become more complex. Three basin families have been identified, each characterized by approximately the same tectono-stratigraphic basin evolution, from a lacustrine/fluvial syn-rift and restricted hypersaline marine transitional period to a shallow to deep marine post-rift, but with varying subsidence patterns and hence varying maturity distributions of the different source rock intervals. Basin family I is characterized by the existence of lacustrine syn-rift and marine post-rift PSTs, and potentially a restricted hypersaline marine PST. Basins belonging to basin family II contain lacustrine syn-rift and restricted hypersaline marine transitional PSTs, and potentially a marine post-rift PST. Basin family III is characterized by the sole development of a lacustrine syn-rift PST. The recognition of basin families allows for analogue comparison between basins with a similar geological background with respect to prospectivity, since similar tectono-stratigraphic basin evolution leads to the development of similar PSTs and plays.

 

 

 

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Figure Caption

Figure 1. Location map of the individual basins along the southeastern Brazilian Margin.

Figure 2. “Facies Palette” providing a general summary of the depositional environments associated with the sequence of basin cycles in the basins along the Brazilian Margin. In each category more proximal environments are shown at the top, and more distal ones below.

Figure 3. Example “Trajectory Plot” for the Campos Basin, which describes the sedimentary evolution (vertical axis) versus basin cycle evolution (horizontal axis): The absolute ages of the basin cycles are shown, as well as the cycle and depositional environment of the source, reservoir, and seal horizons identified. The plus signs indicate a restricted (hypersaline) marine depositional environment.

Figure 4. Simplified “Trajectory Plots”, describing the average basin depositional environment trend of the northern (top) and southern (bottom) basins. Depositional environments in the syn-rift and transitional cycles are rather consistent in these basins, but there is a great variety of mainly shelf to deeper marine environments in the post-rift. The upward trend observed in most basins at the end of the post-rift reflects the additional presence of coastal environments. Note the location of source, reservoir, and seal rock horizons on the trajectory path. Note also the significantly greater variation in the southern basins and the transitional cycle (as represented by a salt sequence in the other basins) that is essentially absent from the Pelotas Basin. The proven presence of a restricted (hypersaline) marine transitional PST in the Sergipe-Alagoas Basin and the similarity of facies in other basins (see trajectory plot) might suggest that it could be present elsewhere.\

Figure 5. Summary of all types petroleum system (PSTs) recognized, hypothetical or speculative, in the basins along the Brazilian Margin. Note the widespread presence of the lacustrine syn-rift PST, the possibly widespread post-rift shallow-deep marine PSTs, and the local development of a transitional PST.

Figure 6. Summary and characterization of the three basin families identified on the basis of petroleum system development along the Brazilian Margin. Note that the Pelotas and Jacuípe basins have not been classified, due to lack of reliable data.

Introduction

Sedimentary basins can be divided into relatively standard tectono-stratigraphic cycles and stages with characteristic hydrocarbon habitats. Therefore, in many cases we can compare petroleum systems in different basins with similar geological histories. This can aid us in recognizing types of petroleum systems (PSTs), as well as the plays associated with them, and thus assist in the evaluation of opportunities in unexplored and under-explored basins. Tools we use in this approach are the facies palette, trajectory plot, events chart, petroleum system flow chart, play characterization diagram, creaming curve and field size distribution diagram.

The Brazilian marginal basins (Figure 1), comprising the Sergipe-Alagoas, Jacuípe, Almada-Camamu, Jequitinhonha, Cumuruxatiba, Espirito Santo, Campos, Santos and Pelotas basins, experienced a similar tectonic and sedimentary basin evolution, comprising a fluvio-lacustrine syn-rift, a fluvio-marine and ultimately restricted (hypersaline) marine transitional cycle, followed by a shallow to deep marine post-rift (Figures 2, 3, and 4).

Basin Cycles

Three of these basin cycles are associated with at least one type of source rock, which form the basis of a specific type of petroleum system (PST) (Figure 5). The lacustrine syn-rift PST is regionally extensive and the most productive. Despite the potentially widespread distribution of transitional and post-rift source rocks, fluvio-marine transitional, restricted (hypersaline) marine transitional, and shallow and deep marine post-rift PSTs have only been proven active locally, due to the relatively low maturity of the source rocks. Potential for a lacustrine pre-rift PST has only been recognized in the Almada-Camamu Basin area.

Play development is closely related to basin tectonic and sedimentary evolution: syn-rift plays are associated with lacustrine/fluvial facies in combination with faulted traps related to graben development. Post-rift plays include deltaic and shallow to deep marine clastic and carbonate facies in combination with traps which formed due to drape above halokinetic structures, and include significant elements of stratigraphic trapping (e.g. turbidities, channels and slope fans). The number and variety of plays increase with basin evolution, as tectonic and sedimentary patterns become more complex.

Three basin families have been identified along the Brazilian Margin, all of which are characterized by approximately the same tectono-stratigraphic basin evolution, from a lacustrine/fluvial syn-rift and restricted (hypersaline) marine transitional period to a shallow to deep marine post-rift, but with varying subsidence patterns and hence varying maturity distributions of the different source rock intervals.

This basin classification is based on PST development, which is strongly controlled by post-rift subsidence and sedimentation. In contrast to the West African Margin, no big rivers enter the area, so in many cases, there is insufficient burial to mature post-rift source rocks. Basin family I, however, is characterized by the existence of lacustrine syn-rift and marine post-rift PSTs, and potentially a fluvio-marine transitional and/or restricted (hypersaline) marine transitional PST. Basins belonging to basin family II contain lacustrine syn-rift and restricted (hypersaline) marine transitional PSTs, and potentially a marine post-rift PST. Basin family III is characterized by the sole development of a lacustrine syn-rift PST. The Pelotas Basin, which lies south of the Rio Grande Fracture Zone, represents an additional fourth basin family. It has no salt-bearing transitional cycle and possibly no lacustrine source rocks in the syn-rift. The Jacuípe Basin also has no salt sequence within the transitional cycle, because the basin was sediment-starved during this period in basin evolution. However, too little has been published about these two basins to allow full evaluation and they have not been reviewed in detail.

The basins discussed here, except for the Pelotas and Jacuípe basins, are collectively characterized by the occurrence of prolific pre- and post-salt source rocks, salt related trapping structures, tectonic tilting and related Tertiary loading. However, exploration density is not uniform across the Brazilian Margin: shelf areas have been extensively explored, while both the syn-rift and post-rift in the deep to ultra-deep water offshore sectors of all basins remain under-explored. The risks concerning the syn-rift mostly involve the distribution and maturity of syn-rift source rocks, complex trapping geometries and poorly known reservoir quality. The main risk for the post-rift is related to the presence or absence of migration pathways from mature syn-rift source rocks to post-rift reservoirs through windows in the evaporites of the transitional cycle. Marine shales within the post-rift are only locally mature.

Conclusion

The Brazilian South Atlantic basins have experienced a similar tectonic and sedimentary basin evolution. This has led to the development of similar PSTs and plays in these basins. The main criterion used for the distinction of different basin families involves the maturity distribution of the potential source rocks, which is strongly controlled by post-rift subsidence and sedimentation. The recognition of basin families in this area allows for analogue comparison between basins with a similar geological background with respect to prospectivity, since similar tectono-stratigraphic basin evolution leads to the development of similar PSTs and plays.

References

Brown, Alistar R., 2004, Reservoir Identification, AAPG Memoir 42 and SEG Investigations in Geophysics, No. 9, Chapter 5, p. 153-197.

Bruhn, C.H.L., and R.G. Walker, 1995, High-resolution stratigraphy and sedimentary evolution of coarse-grained canyon-filling turbidites from the Upper Cretaceous transgressive megasequence, Campos Basin, offshore Brazil: Journal of Sedimentary Research, v. B65, p. 426-442.

Brownfield, M.E. and R.R. Charpentier, 2006, Geology and total petroleum systems of the West-Central Coastal province (7203), West Africa: USGS Report 2207-B: Web accessed 12 February 2010. http://pubs.er.usgs.gov/usgspubs/b/b2207B.

Kristian E. Meisling, Peter R. Cobbold, and Van S. Mount, 2001, Segmentation of an obliquely rifted margin, Campos and Santos basins, southeastern Brazil, AAPG Bulletin, v. 85, no. 11, p. 1903-1924.

Tissot, B., G. Demaison, P. Masson, J.R. Delteil, and A. Combaz, 1980, Paleoenvironment and petroleum potential of Middle Cretaceous black shales in Atlantic basins: AAPG Bulletin, v. 4, no. 12, p. 2051-2063.

 

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