This multiclient study is an example of good integration of high-resolution geochemistry approach with geological data that proved the existence of various petroleum systems, in shallow and deep offshore water areas of Santos Basin.

This study was performed on a selection of 33 crude oils and 12 wells with hundreds of rock samples, of varying organic richness. A 2D basin modeling was performed, based on interpreted seismic line and integration of geochemical and geological data.

This report is fundamental to understand and learn about the geochemical oil types in the offshore Santos Basin, generated from rift associated calcareous black shales of the Guaratiba Formation deposited in saline lacustrine environment during the Upper Barremian/Aptian sequence and later during Albian Cenomanian anoxic marine drift carbonate mudstones of the Guarujá Formation.

2D Basin Modeling results suggest different phases of generation and migration of the rift source rocks mixed at different stages with the drift sequence. This may well explain the presence of cracked hydrocarbons and condensates mixed with oils and genetic links of the oils to different organic matter sediments. Moreover, shallow reservoirs in some cases, have undergone biodegradation and reservoirs have been recharged and mixed with new fresh oils and condensates.

In the deep water offshore, main phase of generation and migration of the rift source rocks occurred in the Early Tertiary and are still in the oil window phase. Lacustrine oils are dominant with respect to marine oils and are more present in the Central and Northern part of the basin.

Full references of all images are listed in the reports

1. Introduction
2. Regional geology and tectonic framework
3. Exploratory history
4. Elements of the petroleum systems
   1. Source rocks and hydrocarbons
      1. Source rock characterization
         1. The lacustrine guaratiba formation
         2. Marine carbonate guarujá formation
         3. Marine-upper cenomanian-turonian itajai-açu formation
      2. Oils characterization
         1. Lacustrine oils
         2. Marine oils
   2. Reservoirs, seals and traps
      1. Guarujá formation
      2. Ilhabela member/itajaí-açu formation
5. Processes of the petroleum systems (modeling)
6. Petroleum systems of the santos basin
   1. Guaratiba-marambaia ()
   2. Guarujá ()
7. Exploratory implications and risks
8. 2D Basin Modeling in the Santos Basin (Line S-1)
   1. Geological characteristics of the cross section
   2. Source rock characteristics
   3. Maturity analysis
   4. Migration analysis
   5. Analysis of the fluid system
   6. Biodegradation risk
9. 2D Basin Modeling in the Santos Basin (Line S-2)
   1. Geological characteristics of the cross section S-2
   2. Source rock characteristics
   3. Maturity analysis
   4. Migration analysis
   5. Analysis of the fluid system
   6. Biodegradation risk
10. Conclusions
11. Appendix
    1. Modeling
    2. Geochemical data
    3. Summary sheets – saturate
    4. Summary sheets – aromatic
    5. Source rocks data

1. Simplified tectonic framework and main hydrocarbon occurrences of the Santos Basin (modified from Pereira & Macedo, 1990).
2. Schematic geologic dip cross section in the Santos Basin (modified from Pereira & Macedo, 1990). See Figure 1 for location.
3. Stratigraphic chart of Santos Basin showing the position of the Guarujá and Guaratiba Formations (modified from Pereira & Feijó, 1994).
4. Geological map of Southeastern Brazil and Southwestern Africa prior to the opening of the Atlantic Ocean (modified from De Wit et al., 1988). Onshore localities are (from southwest to northeast) Florianópolis (FL), Santos (SA), and Rio de Janeiro (RJ) in Brazil; and Luanda (LU) in Africa (Meisling et al., 2001).
5. Tectonostratigraphic events chart for the Campos and Santos basins, showing timing of regional lithostratigraphic packages relative to hotspot, rifting, and structural events. The stratigraphic columns are modified from Rangel et al. (1994) and Pereira & Feijó (1994). Dark yellow/heavy dots = coarse clastic rocks; light yellow/fine dots = fine-grained clastic rocks; brown/dashes = shale and mud rocks; blue/bricks = carbonate rocks; green/squares and green-blue hatchures = evaporites; mixed colors/mixed symbols = mixed lithology; pink/vees = volcanic rocks (Meisling et al., 2001).
6. Tectonostratigraphic events chart for the Campos and Santos basins, showing timing of hot spot, rifting and structural events (Meisling et al., 2001).
7. Map of South Atlantic and adjacent continents showing marine gravity anomalies from satellite altimetry (Sandwell & Smith, 1995), outline of onshore Paraná and Etendeka (EL) lavas, Mid- Atlantic Ridge (MAR), major fracture zones (Rio de Janeiro fracture zone = RJFZ; Florianópolis fracture zone = FFZ) , tracks of Tristão da Cunha and Trindade hot spots ( unfilled circles with ages in Ma), resulting seamounts (TR = Trindade; MV = Martin Vaz; TC = Tristão da Cunha) , and other offshore features (PB = Pelotas Basin; TA = Torres Arch; FP = Florianópolis Platform; RG = Rio Grande Rise; SB = Santos Basin; CB = Campos Basin; AP = Abrolhos Plateau; ES = Espírito Santo Basin; NB = Namib Basin; WB Walvis Basin; LB = Luderitz Basin) . The color bar shows anomaly values in mGal (Meisling et al., 2001).
8. Map of gravity anomalies, Campos and Santos basins. Anomalies are residual, after removal of a fifth-order trend surface from Bouguer-corrected data provided by Lamont- Doherty Geological Observatory. Onshore localities are (from southwest to northeast) Florianópolis (FL), Santos (SA), and Rio de Janeiro (RJ). Main anomalies have been interpreted (MU = nearshore Moho uplift; FS = failed spreading ridge). Dashed lines (TZ) identify some of the more prominent transfer zones; blue dotted lines (TF) prominent fossil ocean ridge transform faults. The color bar shows residual anomaly values in mGal (Meisling et al., 2001).
9. Geoseismic section A-A’ = across nearshore Moho uplift, Campos Basin (modified from Mohriak & Dewey, 1987; Mohriak et al., 1990a). Brasiliano structures were reactivated in oblique extension during rifting and in later far-field compression (see Cobbold et al., 2001).
10. Wells location of the analyzed oil samples. Note the location of new oils (green stars) that will be available in the next report together with the ones discovered over the last two years.
11. Location of the wells in which the rock samples were sampled and analyzed. Observe the location of the new well (orange color) to be analyzed.
12. Map of main rift-related structural provinces, Campos and Santos basins. East–west extension direction (large red arrows) is from plate tectonic reconstructions of the early (Hauterivian) stage of Atlantic opening (Nurnberg & Muller, 1991, Figure 10). Inferred rift transfer zones are not parallel with this extension direction. Torres Arch; BH Badejo High; AP Abrolhos Plateau (Meisling et al., 2001).
13. Rough contours of the major rift depocenters in the Santos Basin based on an interpreted bouguer map from Karner (2000). The depocenters possibly contain the greatest thicknesses of the Guaratiba Formation source rocks.
14. Geochemical log of the 1-BSS-64-BS well, showing Total Organic Carbon and Pyrolysis-Rock-Eval data of the Guarujá and Itajaí-Açu Formations.
15. Geochemical log of the well 1-SPS-17, showing Total Organic Carbon and Pyrolysis-Rock-Eval data of the Guarujá and Itajaí-Açu Formations.
16. Natural series of sediments of the Itajaí-Açu Formation recovered in Santos Basin.
17. Map of thickness of organic-rich sediments of the Itajaí-Açu Formation.
18. Map of the average TOC values for the Itajaí-Açu Formation.
19. Map of average S2 values for the Itajaí-Açu Formation.
20. Oil types from Santos Basin. Although almost all oils have contribution from the rift lacustrine source rocks, only the ones listed as mixed oils present geochemical evidence.
21. Gas chromatograms of the main oil families of the Santos Basin. As can be noted, there is a dominance of n-alkane bimodal distribution in the lacustrine oils probably due to the presence of lacustrine algal organic matter. By contrast, in the marine oils there is the dominance of low molecular weight n-alkanes.
22. M/Z 191 Fragmentograms of oils from Santos Basin, showing some differences in the hopanes distributions between the lacustrine and marine oils.
23. M/Z 217 Fragmentograms of oils from Santos Basin showing the abundance of methyl steranes and C30 steranes of the lacustrine oils related to the marine one.
24. M/Z 259 Fragmentograms of oils from Santos Basin, showing the dominance of TPP polyprenoids over diasteranes in the lacustrine oils and the inverse (TPP<diasteranes) for=”” the=”” related=”” marine=”” one.<=”” li=””></diasteranes)>
25. M/Z 231 and M/Z 245 Fragmentograms of oils from Santos Basin showing the differences between lacustrine and the marine oils. Note the high abundance of C29 Triaromatic steranes in the lacustrine oils compared with the marine ones.
26. Mass chromatograms from metastable ion monitoring of C27 to C30 steranes compounds of oils from Santos Basin. Observe the absence of the marine marker C 30 propyl in the lacustrine oil.
27. M/Z 231 and M/Z 245 Fragmentograms of marine oils from Santos Basin. As can be noted, the TB-2 oil present some evidences of lacustrine character in its composition. Such fact indicates oil mixing, suggesting contribution from the rift lacustrine sequence.
28. The low abundance of methyl steranes suggests lacustrine contribution and oil mixing in the 1-SPS-31 oil. Nevertheless, the abundance o C29 diasteranes suggest also a marine character.
29. Sterane distribution of two mixed oils. Note that the C29 values do not fit with the high API gravity data. The only explanation is contribution of high maturity light lacustrine oils from the rift to these marine oils. The steranes of the lacustrine samples were destroyed by thermal stress.
30. API versus Saturate content of the Santos oils. As it can be observed, the higher the API values the higher is the saturate content, suggesting a thermal maturity control over both parameters. Nevertheless, it could be observe that the lacustrine samples groups together showing the highest saturate content values. The lack of a good correlation between the two parameter, suggest effects of oil mixing.
31. API versus Sulphur content of the Santos oils. Higher the API values lower is the sulfur content suggesting a thermal maturity control over both parameters. Nevertheless, it could be observe that the lacustrine samples groups together showing the lowest API and highest sulfur values. Also the lack of a good correlation between the two parameters suggests again, effects of oil mixing.
32. API Gravity map showing the oils from Merluza and 1-SPS-31 with the highest API values indicating a good correlation between thermal evolutions due to sediment overburden with these physical properties. Indeed the main depocenter of the drift megasequences in the basin occurs adjacent to the area. On the other hand, it is observed that the high values of sulphur content and low API data related to the oils from the wells 1-RJS-81, 1-RJS-539 and 1-BSS-75) is related to biodegradation.
33. Average sulphur content map of the Santos Basin oils. As observed with the API Gravity map, the oils from Merluza and 1-SPS-31 show the lowest sulfur values indicating a break of carbon-sulfur bonds by thermal evolution due to sediment overburden. On the other hand, it is observed that the high values of sulphur content related to the oils from the 1-RJS-81, 1-RJS-539 and 1-BSS-75 wells) is related to biodegradation.
34. Stable carbon isotopic composition of the saturate and aromatic fractions showing no distinction whatsoever among the oil types, suggesting the effects of extreme thermal maturity and also oil mixing (lacustrine contribution to the marine ones).
35. Hopane/sterane ratio versus C27/C29Steranes. As can be noted, the lacustrine oils groups together showing higher C27 steranes and hopanes. The high Hop/Ster ratio presenting by some northern oils (e.g. SPS 31, 21, 6, and EM-2, etc) could suggest a higher degree of mixing with variations in oil composition with higher contribution of the rift condensates. Indeed, northeast of Tubarao occurs a clear thick rift section. Therefore, the Northern oils could have higher degree of mixture than the southern ones.
36. C24 Tetracyclic/ C26 Tricyclic terpanes versus Hopane/ Sterane ratios. As can be noted, the lacustrine oils group together with the oils from northern Santos basin and: differs substantially from the southern ones, suggesting, therefore a higher contribution of the rift for the northern oil accumulations.
37. Hopane/sterane versus Gammacerane ratios. As can be observed the Gammacerane ratio data cannot differentiated the oil types. On the other hand the Hopane/steranes suggest that all oils with values above 2 are either lacustrine or have a great contribution from lacustrine condensates and oils.
38. Mass chromatograms from metastable ion monitoring of C27 to C30 steranes compounds of oils from Santos Basin. Note that the C30 steranes are absent in the lacustrine RJS-539 oil and also in the marine 3-TB-2 one. This parameter is diagnostic marker from a marine algal input. Its absence in the Tubarão 3-TB-2 oil again confirms a great contribution of rift condensates to Tubarão oil accumulation.
39. Oil x Oil correlation, using M/Z 191 data, among three lacustrine saline oils from Santos, Campos and Espírito Santo Basins. Note the great similarity among the terpane distribution, suggesting a common source.
40. Oil–Oil correlation using M/Z 191 and 217 mass fragmentograms of marine anoxic oils from Santos and Espirito Santo basins. As can be noted they are almost identical, showing that the Albian/Cenomanian anoxic marine sequence occur widespread in all the great Campos Basin. In Campos although it is present, there is a maturity limitation for oil generation and expulsion.
41. M/Z 217 Fragmentograms showing the maturity differences between lacustrine and marine oils of the Santos basin. The marine oils show the highest effect of thermal maturity. Again, contribution from the rift could explain such characteristics.
42. The maturity biomarker data of the Santos oils shows a direct relationship between the two biomarker maturity data. Nevertheless, when compared with the API values (see Table 1) there is no correlation in most of the samples. A possible explanation is oil mixing between low cracking marine oils with highly cracked rift oils. Such facts obscure the source effects (lacustrine versus marine character on the bulk parameters). On the other hand there is a correlation between API, saturate contents and thermal maturity (Table 1). Also, the biomarker data suggested that most of the oils were expulsed at least over peak generation stage
43. Map of C29 steranes for oils of the Santos basin. Confirming all the bulk data, the most thermal cracked oils occur in the Merluza and the northern part of the basin. It is worth to mention the high thermal evolution of the oils from the extreme southern part of the basin.
44. Map of TS/(TS+TM) biomarkers for oils of the Santos Basin, showing similar results as observed on the steranes thermal evolution data.
45. Plot of diamondoid and sterane data from condensate and oils from the Santos Basin. As can be noted, almost all samples from Santos basin show oils with low maturity (marine character) mixed with highly cracked oils (lacustrine), confirming therefore, the contribution of the rift oils in the Tubarão and other oil fields in the basin.
46. Gas chromatograms and M/Z 191 mass fragmentograms of oils from Santos basin showing the presence of paleobiodegradation. The presence of 25 norhopanes in the M/Z 191 mass fragmentograms with n-alkanes in the saturate fraction indicates oil biodegradation with subsequent mixing with fresh oil.
47. Map of 25-norhpane index for oils of the Santos Basin. The presence of higher ratios in the oils from the northern part, suggest that reservoir depth and temperature through time have a major role in oil biodegradation and oil mixing.
48. Gas chromatograms of the marine oil families of the Santos Basin. Except the oil from 1-RJS-81, all the other marine oils from Santos Basin do not show biodegraded n-alkanes profile. The high API data of the 1-RJS-81 suggest also, the contribution of fresh oil after biodegradation occurrence.
49. M/Z 191 Mass chromatograms of the marine oil families of the Santos Basin, showing differences due to thermal evolution and probably oil mixing, with contribution from the rift.
50. M/Z 217 Mass chromatograms of the marine oil families of the Santos Basin. By contrast with the M/Z mass 191 fragmentograms (Terpanes) in Figure 49, the steranes show identical profile, therefore indicating thermal destruction of the lacustrine steranes and preservation of the marine ones.
51. M/Z 259 Fragmentograms of oils from Santos Basin. The dominance of TPP polyprenoids does suggest a marine character for this oil type. Again, thermal destruction of these compounds could explain the lower abundance of lacustrine TPP compounds related to diasteranes.
52. Gas chromatograms of the marine oil families of the Santos Basin. Note how similar is their n-alkane distribution, suggesting a very high thermal evolution profile.
53. M/Z 191 Mass chromatograms of the marine oil families of the Santos Bas:in. Although their n-alkanes distribution are identical, the terpanes show a very distinct profile, also suggesting strong effects of thermal stress and higher lacustrine contribution in the Tubarão oils (1-PRS-4).
54. M/Z 217 Mass chromatograms of the marine oil families of the Santos Basin. By contrast with the M/Z mass 191 fragmentograms (Terpanes) in Figure 53, the steranes show identical profile, therefore indicating thermal destruction of the lacustrine steranes and preservation of the marine ones.
55. M/Z 259 Mass chromatograms of the marine oil families of the Santos Basin, showing similar TPP polyprenoids distribution. Again the lacustrine contribution was thermally destroyed.
56. Gas chromatograms of the marine oil families of the Santos Basin showing great similarities among them.
57. M/Z 191 Mass chromatograms of the marine oil families of the Santos Basin showing major differences in the terpane distributions. Such differences are due mainly to thermal evolution and probably to some rift contribution.
58. M/Z 217 Mass chromatograms of the marine oil families of the Santos Basin. By contrast with the M/Z mass 191 fragmentograms (Terpanes) in Figure 57, the steranes show identical profile, therefore indicating thermal destruction of the lacustrine steranes and preservation of the marine ones.
59. M/Z 259 Mass chromatograms of the marine oil families of the Santos Basin. Again, there is a great similarity among the oils.
60. M/Z 191 Mass chromatograms of the marine oil families of the Santos Basin, suggesting some contribution of rift hydrocarbons in some accumulations.
61. M/Z 217 Mass chromatograms of the marine oil families of the Santos Basin. By contrast with the M/Z mass 191 fragmentograms (Terpanes) in Figure 60, the steranes show identical profile, therefore indicating thermal destruction of the lacustrine steranes and preservation of the marine ones.
62. Schematic cross-section showing the entrapment of oil and gas within the porous carbonate facies of the Guarujá Formation in the Tubarão field, southern Santos Basin (modified from Moraes Júnior et al., 1989).
63. Permeability vs. porosity plot for the Guarujá Formation reservoirs in the Tubarão field (Carvalho et al., 1990).
64. Schematic cross section showing the entrapment of gas within the turbidite sandstones of the Itajaí-Açu Fm. and shelf sandstones of the Juréia Fm. in the Merluza field, central Santos Basin (modified from Riddle et al., 1995).
65. Schematic geological cross-section (not to scale) across the 1-BSS-69 heavy oil accumulation, northern Santos Basin, showing the oil entrapment within Eocene turbidites of the Marambaia Formation structured by a faulted anticline over a salt pillow.
66. Map of salt-detached structural domains, Campos and Santos basins.
67. Major rift depocenters of the Santos Basin with the estimated degree of thermal evolution at the top of the Guaratiba Formation. The depocenters were modified from an interpreted bouguer map (Karner, in press), while the thermal evolution was based on a published maturity map of the rift sequence (Pereira & Macedo, 1990).
68. Maturity profile showing vitrinite reflectance data from the Turonian to Albian sequence in several wells drilled in the central/southern Santos Basin (modified from Arai, 1987).
69. Simplified tectonic framework, main hydrocarbon occurrences, and pods of source rocks of the Guaratiba-Marambaia (.) petroleum system (modified from Pereira & Macedo, 1990; and Karner, in press).
70. Events chart of the Guaratiba-Marambaia (.) petroleum system, based on the integration of all the published data.
71. Simplified tectonic framework, main hydrocarbon occurrences, and pod of active source rocks of the Guarujá (.) petroleum system (modified from Pereira & Macedo, 1990; Demercian et al., 1993; and Arai, 1987).
72. Events chart of the Guarujá (.) petroleum system, based on the integration of all the published data.
73. Main geological features influencing petroleum systems, Campos and Santos basins (Meisling, et al., 2001).
74. Summary of the hydrocarbon exploration systems of Santos Basin.