Stratigraphic Evolution, Paleoenvironments and Petroleum Systems of the Dahomey/Benue Basins, Nigeria and the Potiguar/Ceara Basins, NE Brazil

Akande1, S.O. , Adekeye1, O.A., Ojo2, O.J., Adeoye3, J.A., Erdtmann4, B.D. and Koutsoukos5, E.1.Department of Geology, University of Ilorin, Ilorin, Nigeria.2.Department of Geology, Federal University, Oye-Ekiti, Nigeria3.Department of Geology, Mountain Top University, Lagos, Nigeria4.Institute for GeoSciences,Technical University, Berlin, Germany.5.Institute for GeoSciences, University of Heidelberg, Germany.

Presentation Outline Introduction

Regional Stratigraphic Setting , Paleoenvironments

Source Rocks Types, Reservoirs, Seals

Burial Model , Hydrocarbon generation and Expulsion

Exploration Targets / Analogs

Principal Objectives

Compare the Potiguar/Ceara basins stratigraphy, paleoenvironments and petroleum systems with Dahomey/Benue basins based on new knowledge on the tectonics, facies development and subsidence history.

Compare data sets on Source Rocks, Reservoirs, Seals, Traps and Migration Pathways and Timing of Hydrocarbon Generation.

Outline the Similarities and Differences based on New Knowledge.

Enumerate the Exploration Significance of the Comparisons.

Barremian – Albian Paleogeography

Generalized Stratigraphic Correlations

Generalized stratigraphy of the Potiguar Basin (Bertani et al. 1990)

Geology of the On-shore areas of the Potiguar Basin – note the NW /SE Section

Potiguar basin NW – SE Section

Potiguar basin SW – NE Section

Candidate Source Rocks in the Potiguar basin.

Plays within the Acu and Alagamar Formations

Plays in the Pendencia and Alagamar Formations

Regional Relations in the Gulf of Guinea basins

Potiguar Onshore

Reservoir facies of the Albian - Cenomanian Acu Fm.

Reservoir facies – Acu Formation

Acu Formation

Acu Formation

The Cenomanian – Coniacian Jandaira Formation

Dahomey Basin in the context of the Gulf of Guinea

Perspective of the Benue Trough

Geology of the Dahomey Basin showing traverses, boreholes and the X well

QuarryWell/BoreholesMajor towns, cities

Regional Stratigraphy of the Benue Trough

Ise Formation section at Akinjole

Bitumen impregnations in the Afowo Formation.

Pre-transform fault blocks, Syn and Post transform reservoirs, of the Ivory Coast Basin From (Brownfield and Charpentier 2006)

Section of the coasts of Benin and Nigeria’s Eastern DahomeyBasin From Brownfield and Charpentier (2006)

Geology of the Lower Benue region

Abakaliki Shale facies

Eze- Aku Shale

The Lokpanta Shale Section

Awgu Shale and interbeds of Carbonates

Awgu Coal Measures – Middle Benue region

Fanglomerates of the Lower Bima Formation in the Northern Benue area.

Bima Formation on the Lamurde anticline

Petroleum Source Rocks in the Basins

Early Cretaceous ( lacustrine(Kerogen Types I and II )

Late Cretaceous - Lower Paleocene (marine dominated) (Kerogen Types II and III )

Van‐ Krevelen diagrams of source rocks of a. the continental Pendecia Fm and b. the transitional Alagamar Formation , Brazil Potiguar Basin (From Trinidade et al. 1992).

Kerogen classification of the Afowo shales in the Dahomey Basin, Lokpanta, Eze-Aku, Awgu, shales and the Mamu formation coals in the Anambra Basin and the shales of the Bima and Yolde formation in the Gongola Basin ( Data sets for the Gongola Basin are from Akande et al. 1998; Umunna et al. 2002; Obaje et al. 2004 and Abubakar et al 2008).

Reconstructed Thermal and Burial History of one of the offshore well NW Potiguar basin area (Trinidade et al. 1992).

Thermal and Burial History of the offshore X well in the Dahomey basin and the Bende well of the Anambra Basin, Nigeria.

Burial ModelsPotiguar/ Ceara basins• Maturation and transformation of the deeper Neocomian lacustrine Type

I dominated oil prone source beds of the Pendecia Formation commenced at ca. 110Ma (Albian) and the base Neocomian reached the gas window at ca. 65Ma (Paleocene).

• Maturation and transformation of the Aptian – Albian marine hypersalineAlagamar Formation supersource rock with Type I and Type II oil prone Kerogen commenced at ca. 56Ma (Eocene) and still currently in the oil window.

Dahomey / Benue basins• Petroleum source beds of the Neocomian Ise Formation with potential

Type I facies, the Cenomanian - Turonian Afowo Type II dominated oil prone facies (Dahomey basin ), the Lokpanta / Eze-Aku Type II oil prone facies commenced generation at ca. 85Ma ( Late Santonian) and reached the peak of the oil window at ca. 30Ma ( Oligocene).

PETROLEUM SYSTEM CHARACTERISTICS

POTIGUAR/CEARA BASINS DAHOMEY BASIN BENUE BASINS

Source Rock Major Source: Neocomian Pendencia Fm; Aptian AlagamarFm.

Neocomian Ise Fm.; Cen. –Coniacian Afowo Fm. And Camp. – Maastrich. Araromi Shales

Shales of the Asu, Eze-Aku, Awgu and Nkporo Fms. (L. Benue) and the Bima, Fika Shales (U.Benue)

Reservoir Units Albian Acu Fm. –major reservoir, Alagamar Sandstones & the, Pendencia Sandstone units

Ise fluvial sandstones, Afowo, Sandstone turbidites.

Sandstone units of the Asu River, Eze-Aku, Agbani and the Owelli sandstone facies.

Regional Seals Albian Ponte de Mel Fm. Cen. –Coniacian Jandaira Fm.

The Afowo Shale, Araromi Shale and Imo Shale.

Eze-Aku , Awgu, Imo Shale; Fika Shale in the U. Benue

Potential Traps Fault traps, Unconformity related trap systems and stratigraphic traps

Normal faults, Unconformity related and Fold structures with stratigraphic traps on lapped pinchouts.

Normal faults, Unconformity related and Fold structures with stratigraphic traps

HC Expulsion Time Burial History suggests periods between ca. 110Ma (Albian) and 65Ma (Paleocene) for the Pendencia and 56Ma (Eocene) for the Alagamar.

Ise and Afowo Source beds were generative since 85Ma (Santonian) and would have expelled to the peak of oil window at 30Ma (Oligocene) consequent to high rate of subsidence of the Paleocene.

The Bima, Fika, Asu, Eze-Aku, Awgu Formations were also generative since 83Ma (Early Campanian) with the peak of the oil generation window attained at ca. 30Ma Oligocene. The Nkporo Shale was generative at ca.50Ma (Eocene).

Migration Fairways Fault structures and Unconformity related paths.

Normal Fault structures, Unconformities and fold structures.

Normal Fault structures, Unconformities and fold structures.

Summary Table of Petroleum System Characteristics

Concluding Remarks• The Stratigraphy andSubsidence history of the basins confirm extensional origin

for the Potiguar/Ceara and the Dahomey basins.• Fault controlled subsidence dominate the Brazilian marginal basins and the

Dahomey basins thereby controlling the overall facies distribution and the evolution of thick sequences of Neocomian rift sediments before the marine influences which deposited the marine-hypersaline source rocks of the AptianAlagamar Fm.; Lesser thicknesses of rift sediments occur in the Dahomey/Benue basins.

• Drift sediments accompanying the Albian-Cenomanian period formed the major reservoir for the expelled hydrocarbons of the Potiguar /Ceara basins and could represent potential reservoir units for hydrocarbons generated in the Early Cretaceous and time equivalent source rocks of the Dahomey/Benue basins.

• Large volumes of hydrocarbons were generated and expelled in the basins as reflected in the burial history for the basins which shows that: The NeocomianPendencia source rocks was in the oil window between 110Ma (Albian) and 65Ma (Paleocene) and the Aptian Alagamar source reached the oil window at ca. 56Ma (E.Eocene) till present. The Neocomian Ise and Afowo Fms . including the Bima, Eze Aku and Awgu were generative from ca. 85Ma ( Santonian and reached the peak of oil generation at ca. 30Ma (Oligocene).

• The comparative study suggest that valid petroleum systems exist in the basins with relative differences in the subsidence history, facies developments, generation and expulsions periods of hydrocabon generation.

Thank you