Guardado, L. R., A. R. Spadini, J. S. L. Brandão, and M. R. Mello, 2000, Petroleumsystem of the Campos Basin, in M. R. Mello and B. J. Katz, eds., Petroleumsystems of South Atlantic margins: AAPG Memoir 73, p. 317–324.

Chapter 22

Petroleum System of the Campos Basin,Brazil

Abstract

The Campos Basin, located offshore from Rio de Janeiro in southeastern Brazil, is the most prolificpetroleum-bearing basin in Brazil. To date, Petrobrás has discovered more than 70 hydrocarbon accumu-lations in the basin, including seven giant oil fields in deep water. The Campos Basin accounts for morethan 80% of the total exploitable Brazilian reserves and 75% of total oil production. The Barremian calcare-ous shales from the Lagoa Feia Formation are the source rocks of all the oil in the basin. Accumulationsoccur in a variety of siliciclastic and carbonate reservoirs, ranging from Barremian to Miocene in age.Upper Cretaceous–Tertiary turbidities contain most of the oil, but Neocomian basalts also containcommercial accumulations. Peak oil generation occurred during late Miocene time, and the most impor-tant migration pathways are through salt windows and along listric faults.

INTRODUCTION

The Campos Basin covers an area of about 100,000 km2

(up to the 3400-m isobath). The oil fields discovered occurin water depths ranging from 80 m to more than 2600 m(Figure 1).

Because of its importance as a petroleum province,many papers have been published identifying and char-acterizing the petroleum system of the Campos Basin(e.g., Meister, 1984; Guardado et al., 1989; Mohriak et al.,1990; Mello et al., 1994). The abundance of petroleum inthis basin is the result of the existence in time and spaceof all the elements and processes necessary for a world-class petroleum system. These include (1) rich, oil-pronesource rocks, (2) the presence of effective migration path-ways, (3) excellent reservoirs, (4) effective traps and seals,and (5) the appropriate timing for trap formation and oilmigration. This study is a geologic, geophysical, andgeochemical investigation of the elements and processesmaking up the petroleum system of the Campos Basin. Inaddition, geochemical results from a large number ofsediment cores, cuttings, and oil samples recovered from

the Lagoa Feia Formation are discussed. The objective isto identify and characterize the key elements thatcontributed to the establishment of the most prolificpetroleum system in Brazil.

TECTONO-STRATIGRAPHIC SETTING

The Campos Basin was formed as a result of thebreakup of Gondwana in the Early Cretaceous. This wasfollowed by subsequent infilling of the rift basin with asmuch as 9000 m of Early Cretaceous–Holocene sedi-ments, as shown in the stratigraphic chart of Figure 2. Thebasin has several main structural elements (Figure 3): (1)northeast- and northwest-trending horsts and grabensmapped at the Neocomian basalt reflector; (2) pre-Aptianstructures related to the Campos fault; and (3) a salt domeprovince, which is an extension of the São Paulo Plateauin ultra-deep water.

The sedimentary section of the Campos Basin can besubdivided into three megasequences. (Figure 2). First,

317

L. R. Guardado

A. R. Spadini

J. S. L. Brandão

Petrobrás E&PRio de Janeiro, Brazil

M. R. Mello

Petrobrás–CenpesRio de Janeiro, Brazil

the nonmarine rift megasequence is composed of lacustrineBarremian sedimentary rocks overlying Neocomianbasalts. The strata were deposited in a variety of paleo-environments that were strongly influenced by rifttectonics. These included alluvial fans, fan deltas,carbonate banks, and lacustrine environments rangingfrom brackish to hypersaline. This sequence contains thecalcareous shales of the Lagoa Feia Formation, the mostimportant source rock in the basin. Second, the transi-tional megasequence was deposited in Aptian time duringa period of tectonic quiescence. It represents the begin-ning of the drift phase and contains a lower sequence,mostly composed of conglomerates and carbonates, andan upper sequence consisting of halite and anhydrite.Third, the marine megasequence is made up of Albianshallow-water carbonates, mudstones, and marls(Macaé Formation) at its base. This basal sequencegrades upward into an Upper Cretaceous–Paleocenebathyal sequence consisting of shales, marls, and sand-stone turbidites. A progradational siliciclastic sequencecharacterizes the remaining Neogene section. The depo-sition of this megasequence was strongly affected by salttectonics.

SOURCE ROCKS AND HYDROCARBONCHARACTERIZATION

Figure 4 shows a geochemical log from a selectedCampos Basin well that indicates the excellent hydrocar-bon source potential of the Lagoa Feia Formation. TheBarremian Lagoa Feia section is composed of well-lami-nated shales interbedded with carbonates. It ranges inthickness from 100 to 300 m, with typical total organiccarbon (TOC) values averaging 2–6% and locally as highas 9%. The hydrogen indices (HI) are up to 900 mgHC/mg TOC, consistent with type I kerogen (Figure 4).Organic petrography shows the predominance oflipid-rich material mainly of algal and bacterial origin. Onaverage, the organic-rich beds contain about 90% amor-phous organic matter (Mello et al., 1994).

Gas chromatography (GC) and gas chromatogra-phy–mass spectrometry (GCMS) data were obtainedfrom the oils and organic extracts from the organic-richsections of the Lagoa Feia Formation (Figure 5). Thebiological marker distribution (Figure 6) suggests lacus-trine brackish to saline depositional environments.

318 Guardado et al.

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Characteristics include the dominance of low molecularweight n-alkanes with a slight odd-carbon predomi-nance; pristane greater than phytane; heavy δ13C values(between –22 and –25‰); high concentrations of highmolecular weight tricyclic terpanes (up to C40), C30 dino-steranes, β-carotane, 28,30-bisnorhopane, and 4-methyl

steranes; a low hopane/sterane index; and Ts/Tm < 1(Figures 5 and 6) (Mello, 1988; Mello and Maxwell, 1990;Mello et al., 1994). The diagnostic molecular features thatcharacterize the lacustrine marine-influenced systems inthe Lagoa Feia Formation are the presence and abun-dance of 24-n-propylcholestanes. Such compounds are

Chapter 22—Petroleum System of the Campos Basin, Brazil 319

LITHOSTRATIGRAPHY

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Figure 2—Stratigraphic chart of the Campos Basin.

considered to be marine source indicators, derived frommarine Chrysophytae algae (Moldowan et al., 1990; Melloand Hessel, 1998).

Most of the Campos Basin oils have API gravitiesranging from 17–37° API and consist of a mixture ofbiodegraded and nonbiodegraded oils. This mixtureresulted from more than one generation and migrationpulse, coupled with biodegradation episodes thatoccurred during successive stages of reservoir filling(Soldan et al., 1995).

Reconstruction of the paleoenvironment of the LagoaFeia Formation, based on bivalve and sedimentologicdata (Carvalho et al., 1996), suggest the occurrence duringthe early Neocomian of small, interior brackish to salinealkaline lakes (without marine influence) and a largeepicontinental water body (possibly a restricted gulf orlagoon). Intermittent sea water incursions into the water

body brought about the onset of marine depositionalconditions, eventually resulting in the emergence of typi-cal marine bivalve species (Agelasina and Remondia)(Mello and Hessel, 1998). Blooms of cyanobacteria coin-cided with increased water salinity. This may have led tomass mortality of the benthic bivalves as a result of therelease of cell toxins into the water (Brong-ersma-Sanders, 1957) and/or the reduction of watercolumn oxygenation resulting from algae senescence anddecay. These bloom cycles with a high biomass ofcyanobacteria led to the deposition of the organic-richshales that form the source rocks of the Lagoa FeiaFormation (Mello and Hessel, 1998).

Paleozoologic data from coquinas indicate that duringthe late Barremian, the euryhaline bivalve Arcopagelladominated the epicontinental waters of the CamposBasin. In the early Aptian, a mixohaline species of

320 Guardado et al.

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Figure 3—Structural framework map of the rift section in the Campos Basin. From Rangel and Martins (1998).

Camposella dominated the bottom waters in extremelyhigh abundance. During the middle Aptian, thesemeridional waters extended to the northeast away fromthe continent, and the marine bivalves Agelasina andRemondia appeared, reflecting increased salinity (Melloand Hessel, 1998). These observations are consistentwith isotopic ratios (δ13C) of organic matter from theLagoa Feia shales, which show a tendency toward morepositive values higher up in the sequence, also suggest-ing progressively increasing water salinity (Carvalho etal., 1996).

RESERVOIRSReservoir rocks with good to excellent permeability

and porosity are widespread in the Campos Basin both intime and space. The Barremian carbonates (coquinas) ofthe rift sequence have porosities reaching 15–20% andpermeabilities as high as 1 darcy (d). The best reservoirsconsist of high-energy bivalve grainstones having inter-granular porosity. Grainstones and packstones withsecondary porosity (moldic–vugular) also constitute

reservoirs, as do Neocomian basalts in which vesicles andfractures have created high porosity and permeability.

The Albian shallow-water shelf carbonates comprise abroad spectrum of reservoirs. The highest quality units,with porosities up to 28% and permeabilities of >1 d, arerelated to oolitic facies deposited in a high-energy envi-ronment. There has been little secondary cementation, andtherefore much of the original intergranular porosity hasbeen preserved. Porous (up to 30%) but less permeable(up to 100 md) reservoirs are related to oncolitic–peloidalpackstones and grainstones deposited in a shallow marineenvironment with moderate water agitation. Fine-grainedlimestones deposited in a deeper and lower-energy settingalso constitute reservoirs, but despite their high porosities(20–30%), they have relatively low permeabilities (maxi-mum of a few millidarcys).

The Upper Cretaceous turbidites were depositedmainly in gentle slope troughs formed as a result ofhalokinesis. On the basis of foraminifera, paleobathyme-try ranged from upper to lower bathyal. Porosities rangefrom 20 to 25% and permeabilities from 100 md up to 5 d.

The main Tertiary siliciclastic reservoirs (Oligocene–Miocene) are predominantly medium- to fine-grained

Chapter 22—Petroleum System of the Campos Basin, Brazil 321

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sandstones with porosities of about 30% and permeabili-ties of several darcys. These turbidite complexes devel-oped as extensive basin-floor fans. Locally, there are alsomass-wasting deposits and cross-bedded sandstonesformed from tidal reworking.

PETROLEUM SYSTEM

The vast oil reserves of the Campos Basin are directlyrelated to the widespread occurrence of the prolificBarremian lacustrine source rocks of the Lagoa FeiaFormation. Petroleum generation began in Santonian–Coniacian time, reached its peak during the late Miocene,and continues until the present day (Mello et al., 1994).The oil fields located within the rift section are associatedwith intrabasinal highs, where fault movements createdmonoclinal structures that plunge basinward (Guardadoet al., 1989). The oil migrated laterally from adjacentorganic-rich calcareous shales and accumulated in porouscoquinas that were deposited on the flanks of regionalhighs.

Most of the oil discovered in the Campos Basin (40billion bbl of oil in place, with reserves estimated at 10.7billion bbl) (Lucchesi and Gontijo, 1998) is related to the

Lagoa Feia–Carapebus(!) petroleum system. The eventschart for this petroleum system is shown in Figure 7. Themain fields, including Marlim and Barracuda (Tertiaryreservoirs) and Roncador (Cretaceous reservoir), arelocated at water depths between 250 and 2600 m. Thegiant Tertiary oil fields are predominantly stratigraphictraps (Lucchesi et al., 1995) controlled by the lateral pinch-out of turbidite reservoirs to the west and by regionaldips toward the east. Seismic amplitude anomalies havedelineated oil-saturated Oligocene turbidite reservoirs, asseen in Figure 8. Identification of these anomalies hassubstantially lowered exploration risk in the CamposBasin (Guardado et al., 1997). Although halokinesis hasnot played a major role in defining reservoir geometryand facies distribution, it has played an important role indetermining trap geometry (Rangel and Martins, 1998).

Discovered in 1996, the Roncador field is the largestfield reservoired within Cretaceous (Maastrichtian)turbidites in the basin. Its geometry is complex and ispredominantly controlled by accommodation spacerelated to halokinesis and preservation from subsequenterosion (Santos et al., 1998). It is important to note thatonly the uppermost reservoir zone displays a seismicamplitude anomaly (Figure 9). This is not observed inlower parts of the reservoir (Rangel et al., 1998).

Synchronous generation and entrapment provided thefavorable conditions for establishment of the prolificLagoa Feia–Carapebus(!) petroleum system. The hydro-carbon migration model for the postsalt sequence (Figure10) includes migration from Barremian rift source rocksthrough salt windows and upward along listric faults(e.g., Meister, 1984; Mohriak et al., 1990; Mello et al., 1994).

CONCLUSIONS

All essential petroleum system elements and processeshave resulted in one of the most prolific hydrocarbonprovinces within the South Atlantic sedimentary basinsystem.

322 Guardado et al.

DIASTERANES

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Figure 5—GC and GCMS data for a typical oil from theCampos Basin sourced from the calcareous organic-richsection of the Lagoa Feia Formation.

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Figure 6—Plot of GCMS-MS data for South Atlantic marginoils and organic-rich extracts. Note the distribution of thelacustrine saline samples from the Campos Basin.

These include the following:

• Excellent lacustrine saline source rocks (LagoaFeia Formation)

• High-quality Cretaceous–Tertiary turbidite sand-stone reservoirs (Carapebus Formation)

• Effective traps created by halokinesis associatedwith excellent seals

• Salt windows and related listric fault systemsassociated with good carrier beds allowingmigration from source rock to trap

• Synchronous generation and trap formation asso-ciated with an adequately focused drainagesystem.

REFERENCES CITED

Brongersma-Sanders, M., 1957, Mass mortality in the sea:GSA Memoir 67, n. l, p. 941–1010.

Carvalho, M. D., U. M. Praca, J. L. Dias, A. C. Silva-Telles, T.Horschutz, M. H. R. Hessel, M. S. Scuta, A. S. C. Barbosa,L. C. S. Freitas, and A. D. Sayad, 1996, Coquinas daformação Lagoa Feia da bacia de Campos estudo sedi-mentológico na caracterização da qualidade de reser-vatório: Petrobrás Internal Report, Rio de Janeiro, 188 p.

Guardado, L. R., L. A. P. Gamboa, and C. F. Lucchesi, 1989,Petroleum geology of the Campos Basin, Brazil: a modelfor producing Atlantic type basins, in J. D. Edwards andP. A. Santogrossi, eds., Divergent/passive margin basins:AAPG Memoir 48, p. 3–80.

Guardado, L. R., B. Wolff, and J. S. L. Brandao, 1997, CamposBasin, Brazil, a model for a producing Atlantic basin: OTCProceedings, 1997 Offshore Technology Conference,Houston, Texas, p. 457–462.

Lucchesi, C. F., and J. E. Gontijo, 1998, Deep water reservoirmanagement: the Brazilian experience: OTC Proceedings,1998 Offshore Technology Conference, Houston, Texas, p.625–628.

Lucchesi, C. F., C. C. Martins, C. A. Costa, and L. R.Guardado, 1995, 3-D seismic as an exploration andproduction tool: the Campos Basin experience: OTC

Proceedings, 1995 Offshore Technology Conference,Houston, Texas, p. 507–512.

Meister, E. M., 1984, Geology of petroleum in Campos Basin,Brazil (abs.): AAPG Bulletin, v. 68, n. 4, p. 506.

Mello, M. R., 1988, Geochemical and molecular studies of thedepositional environments of source rocks and theirderived oils from the Brazilian marginal basins: Ph.D.dissertation, Bristol University, Bristol, U.K., 240 p.

Mello, M. R., and M. H. Hessel, 1998, Biological marker andpaleozoological characterization of the early marine incur-sion in the lacustrine sequences of the Campos Basin,Brazil (abs.): Extended Abstracts Volume, AAPG AnnualConvention, Salt Lake City, Utah, v. 2, A455.

Mello, M. R., and J. R. Maxwell, 1990, Organic geochemicaland biological marker characterization of source rocks and

Chapter 22—Petroleum System of the Campos Basin, Brazil 323

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Figure 7—Events chart for the petroleum system of theCampos Basin.

Figure 8—Part of a seismic section from the CamposBasin showing amplitude anomalies related to the oil-saturated Oligocene and Eocene turbidite reservoirs.

- 10000 AMPLITUDE 10000

- 2400

- 2500

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Figure 9—Part of a seismic section showing the amplitudesignature of the Roncador oil field in the Campos Basin.

oils derived from lacustrine environments in the Braziliancontinental margin, in B.J. Katz, ed., Lacustrine basinexploration—case studies and modern analogs: AAPGMemoir 50, p. 77–99.

Mello, M. R., W. U. Mohriak, E. A. M. Koutsoukos, and G.Bacoccoli, 1994, Selected petroleum systems in Brazil, inL. B. Magoon and W. G. Dow, eds., The petroleumsystem—from source to trap: AAPG Memoir 60, p.499–512.

Mohriak, W., M. R. Mello, J. F. Dewey, and J. R. Maxwell,1990, Petroleum geology of the Campos Basin, offshoreBrazil, in J. Brooks, ed., Classic petroleum provinces:Geological Society of London Special Publication,p. 119–142.

Moldowan, J. M., F. J. Fago, C. Y. Lee, S. R. Jacobson, D. S.Watt, N. E. Slougui, A. Jeganathan, and D. C. Young, 1990,Sedimentary 24-n-propylcholestanes, molecular fossilsdiagnostic of marine algae: Science, v. 247, p. 309–312.

Rangel, H. D., and C. C. Martins, 1998, Main exploratorycompartments, Campos Basin, in Searching for oil and gasin the land of giants: Search, Rio de Janeiro, Schlumberger,p. 32–40.

Rangel, H. D., P. R. Santos, and C. M. S. P. Quintaes, 1998,Roncador field, a new giant, in Campos Basin, Brazil: OTCProceedings, 1998 Offshore Technology Conference,Houston, Texas, p. 579–587.

Santos, P. R., H. D., Rangel, C. M. S. P. Quintaes, and J. M.Caixeta, 1998, Turbidite reservoir distribution in Roncadorfield, Campos Basin, Brazil (abs.): Extended AbstractsVolume, AAPG International Conference & Exhibition,Rio de Janeiro, p. 290.

Soldan, A. L., J. R. Cerqueira, J. C. Ferreira, L. A. F. Trindade,J. C. Scarton, and C. A. G. Corá, 1995, Giant deep water oilfields in Campos Basin, Brazil: a geochemical approach:Revista Latino-Americana de Geoquímica Orgânica, v. 1,n. 1, p. 14–27.

324 Guardado et al.

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