Assessment of Undiscovered Oil and Gas Resources of the Niger Delta Province, and Cameroon, Africa

By Michael E. Brownfield

M ED ATLANTIC ITE RRAN OCEAN EAN SEA

INDIAN OCEAN Niger Delta

SOUTH ATLANTIC OCEAN

INDIAN OCEAN

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Chapter 5 of Geologic Assessment of Undiscovered Hydrocarbon Resources of Sub-Saharan Africa Compiled by Michael E. Brownfield

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Digital Data Series 69–GG

U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior SALLY JEWELL, Secretary U.S. Geological Survey Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia: 2016

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Suggested citation: Brownfield, M.E., 2016, Assessment of undiscovered oil and gas resources of the Niger Delta Province, Nigeria and Cameroon, Africa, in Brownfield, M.E., compiler, Geologic assessment of undiscovered hydrocarbon resources of Sub-Saharan Africa: U.S. Geological Survey Digital Data Series 69–GG, chap. 5, 20 p., http://dx.doi.org/10.3133/ds69GG.

ISSN 2327-638X (online) iii

Contents

Abstract...... 1 Introduction...... 1 Geology of the Niger Delta Province, Nigeria and Cameroon, Africa...... 6 Tectonics...... 6 Depositional History...... 6 Petroleum Occurrence in the Niger Delta Province, Nigeria and Cameroon, Africa...... 9 Source Rocks...... 10 Reservoirs...... 12 Traps and Seals...... 13 Exploration...... 16 Geologic Model...... 16 Resource Summary...... 18 For Additional Information...... 18 Acknowledgments...... 18 References...... 19

Figures

1. Map of Nigeria and Cameroon and the Niger Delta showing Niger Delta Province...... 2 2. Map showing extent of the Agbada Assessment Unit (71920101) and the Akata Assessment Unit (71920102)...... 3 3. Map showing generalized geology of West Africa...... 4 4. Map showing geology of the Gulf of Guinea and the Niger Delta, Africa...... 5 5. Paleotectonic maps showing the evolution of continental margins of West Africa and South America...... 7 6. East-west cross section through the Niger Delta region...... 8 7. South-north cross section through the Niger Delta region...... 9 8. Stratigraphic section of the Anambra Basin from Late Cretaceous through Eocene...... 10 9. Cross section of the Niger Delta, Africa...... 11 10. Map showing coastline progradation of the Niger Delta since 35 Ma...... 12 11. Sequence-stratigraphic model for the central portion of the Niger Delta...... 13 12. Subsurface depth to top of Niger Delta oil kitchen...... 14 13. Burial-history chart for the northern portion of the Tertiary Niger Delta (Akata-Agbada)...... 15 14. Slope edge normal-fault simulation (2 Ma to present) of the Niger Delta...... 16 15. Diagram of oil field structures and associated trap types, Niger Delta, Nigeria and Cameroon, Africa...... 17 16. Events chart for the Tertiary Niger Delta Petroleum System (719201) and the Agbada and Akata Reservoirs Assessment Units (71920101, 71920102)...... 18 iv

Table

1. Niger Delta Province and Agbada and Akata Reservoirs Assessment Units results for undiscovered, technically recoverable oil, gas, and natural gas liquids...... 19

Abbreviations Used in This Report

ft foot km kilometer Assessment of Undiscovered Oil and Gas Resources of the Niger Delta Province, Nigeria and Cameroon, Africa

By Michael E. Brownfield

Abstract to turbidites. The Eocene marine mudstone and shale rocks are the primary reservoir seals in both Agbada and Akata The main objective of the U.S. Geological Survey’s Assessment Units. The Niger Delta Province is considered National and Global Petroleum Assessment Project is to assess mature for oil and gas; therefore, current field histories were the potential for undiscovered, technically recoverable oil used as a partial guide for undiscovered sizes and numbers. and natural gas resources of the United States and the world. The U.S. Geological Survey estimated mean volumes As part of this project, the U.S. Geological Survey completed of undiscovered, technically recoverable conventional oil an assessment of the Niger Delta Province, an area of about and gas resources for the Agbada Reservoirs Assessment 292,407 square kilometers. This assessment was based on Unit in the Niger Delta Province at 1,616 million barrels of data from oil and gas exploration wells, oil and gas fields, oil, 9,454 billion cubic feet of gas and 494 million barrels of and published geologic reports. natural gas liquids. The estimated mean size of the largest The Niger Delta Province is a priority province for the oil field that is expected to be discovered is 274 million National and Global Petroleum Assessment Project. The barrels of oil, and the estimated mean size of the expected largest gas field is 981 billion cubic feet of gas. The assessment was geology based and used the total petroleum estimated mean volumes for the Akata Reservoirs AU are system concept. The geologic elements of a total petroleum 13,918 million barrels of oil, 48,767 billion cubic feet of gas, system consist of hydrocarbon source rocks (source-rock and 5,832 million barrels of natural gas liquids; estimated maturation and hydrocarbon generation and migration), mean sizes of the largest oil and gas fields are 4,119 million reservoir rocks (quality and distribution), and traps for barrels of oil and 13,355 billion cubic feet of gas, respectively. hydrocarbon accumulation. Using these geologic criteria, the For this assessment, a minimum undiscovered field size of U.S. Geological Survey defined the Tertiary Niger Delta Total 1 million barrels of oil equivalent was used for the Agbada Petroleum System with two assessment units, the Agbada Reservoirs AU and a minimum undiscovered field size of Reservoirs and the Akata Reservoirs Assessment Units, 5 million barrels of oil equivalent was used for the Akata encompassing 99,915 square kilometers and 212,652 square Reservoirs Assessment Unit. No attempt was made to estimate kilometers, respectively. The Agbada Reservoirs Assessment economically recoverable reserves. Unit was assessed to a water depth of 200 meters and the Akata Reservoirs Assessment Unit was assessed to 4,000 meters water depth. Hydrocarbons were generated from Eocene paralic Introduction and prodeltic Type II and Type III kerogen, ranging from 1.4 weight percent to 5.2 weight percent total organic carbon, The main objective of the U.S. Geological Survey’s and possibly from Cretaceous marine and lacustrine sources. (USGS) National and Global Petroleum Assessment Project is Generation began in the Eocene and continues to the present. to assess the potential for undiscovered, technically recover- Generation moved progressively from north to south as able oil and natural gas resources of the United States and the younger units entered the oil window. Hydrocarbons migrated world (U.S. Geological Survey World Conventional Resources into Eocene Agbada Formation sandstone reservoirs and Assessment Team, 2012). As part of this project, the USGS traps. Hydrocarbons have also migrated into Akata Formation recently completed an assessment of the Niger Delta turbidite sandstones, including lowstand channels, sheet sand, Province (fig. 1), an area of about 292,407 square kilometers and fans. In the Agbada Assessment Unit, hydrocarbon traps (km2). This assessment was based on data from oil and gas are mostly structural, but stratigraphic traps are also present, exploration wells, fields (IHS Energy, 2008), and published whereas in the Akata Assessment Unit traps are mostly related geologic reports. 2 Assessment of Undiscovered Oil and Gas Resources of the Niger Delta Province, Nigeria and Cameroon, Africa

2°E 4°E 6°E 8°E 8°N

NIGERIA BENIN Trough Benue-

Benin Flank TOGO Anambra Basin 200 Dahomey 6°N 2,000 Basin Gulf of Guinea 3,000 Abakaliki High CAMEROON 2 Flank

4,000 Niger Delta 4°N 7192 200

2 2

2,000 EQUATORIAL 3,000 GUINEA 2 2°N 2,000

200

Cameroon Volcanic Line SAO TOME AND PRINCIPE

ATLANTIC 2 OCEAN 0°

4,000 3,000 GABON

Base from U.S. Geological Survey digital data, 2002 0 50 100 KILOMETERS World Geodetic System 1984 (WGS 84) Prime Meridian, Greenwich, 0° 0 50 100 MILES

AFRICA

EXPLANATION NIGERIA Niger Delta province boundary Niger Delta 7192 3,000 Bathymetric contour—Contour depth is in meters. Contour interval varies 2 Sediment thickness contour—Contour is in kilometers. Contour interval varies INDEX MAP

Figure 1. Nigeria and Cameroon, the Niger Delta Province boundary, bounding structural features, and 200-, 2000-, 3000-, and 4000-meter bathymetric contours.

This province was assessed previously as part of the reservoir rocks (quality and distribution), and traps for USGS World Assessment 2000 (U.S. Geological Survey World hydrocarbon accumulation. Using these geologic criteria, Energy Assessment Team, 2000), resulting in estimated mean the USGS defined the Tertiary Niger Delta Total Petroleum undiscovered volumes of 40.5 billion barrels of oil (BBO), System (TPS) with two assessment units, the Agbada 133.7 trillion cubic feet (TCF) of gas, and 6.03 billion barrels Reservoirs Assessment Unit (AU) and the Akata Reservoirs of natural gas liquids (BBNGL). AU (figs. 1, 2), encompassing 99,915 km2 and 212,652 km2, The Niger Delta Province was reassessed because of respectively. The Agbada Reservoirs AU was assessed to continued interest in its future oil and gas resource potential. a water depth of 200 m and the Akata Reservoirs AU was The assessment was geology based and used the total assessed to 4,000 meters (m) water depth. \\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch05_figures\ch05_figures\ch05_figure01.aipetroleum system concept. The geologic elements of a total Two previous USGS geologic studies have reported petroleum system include hydrocarbon source rocks (source- on the potential for undiscovered hydrocarbon resources rock maturation and hydrocarbon generation and migration), and described the petroleum system, assessment units, Introduction 3

2°E 4°E 6°E 8°E 8°N

NIGERIA BENIN Trough Benue-Abakaliki

Benin Flank TOGO Anambra Basin 200 Dahomey 6°N 2,000 Basin Gulf of Guinea 3,000 Abakaliki High CAMEROON Calabar Flank

4,000 Niger Delta 4°N 7192 200

2,000 EQUATORIAL 3,000 GUINEA

2°N 2,000

200

Cameroon Volcanic Line SAO TOME AND PRINCIPE ATLANTIC OCEAN 0°

4,000 3,000 GABON

Base from U.S. Geological Survey digital data, 2002 0 50 100 KILOMETERS World Geodetic System 1984 (WGS 84) Prime Meridian, Greenwich, 0° 0 50 100 MILES

AFRICA EXPLANATION NIGERIA Agbada Reservoirs Assessment Unit Niger Delta 7192 Akata Reservoirs Assessment Unit Niger Delta Province boundary 3,000 Bathymetric contour—Contour depth is INDEX MAP in meters. Contour interval varies Figure 2. Extent of the Agbada Reservoirs Assessment Unit (71920101) and the Akata Reservoirs Assessment Unit (71920102). The Agbada Reservoirs Assessment Unit overlies the Akata Reservoirs Assessment Unit, in part subaerially.

hydrocarbon source rocks, reservoir rocks, and potential outcrops on the Abakaliki High and Calabar Flank—a hinge traps for hydrocarbon accumulation for the province (Tuttle, line bordering adjacent Precambrian rocks in Cameroon Brownfield, and Charpentier, 1999; Tuttle, Charpentier, and terrain (figs. 1, 2). The offshore boundary of the province is Brownfield, 1999). Geologic maps of west Africa and the Gulf defined by the Cameroon volcanic line on the southeast and of Guinea are shown in figures 3 and 4. the eastern boundary of the Dahomey Embayment (fig. 4) to The northern boundary of the Niger Delta Province is the the west. The 2-kilometer (km) sediment thickness contour \\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch05_figures\ch05_figures\ch05_figure02.ai Benin flank (figs. 1, 2)—an east-northeast trending hinge line or the 4000-m bathymetric contour in areas where sediment south of the West Africa Nigerian Massive Province (figs. 3, thickness is greater than 2 km defines the boundary to the 4). The northeastern boundary is defined by Cretaceous south and southwest. 4 Assessment of Undiscovered Oil and Gas Resources of the Niger Delta Province, Nigeria and Cameroon, Africa

18°W 12°W 6°W 0° 6°E 12°E 18°E 24°E

Iullemmeden Chad Taoudeni 7055 7066 Basin 7035 12°N

Senegal Volta 7013 Nigerian West African 7114 West African CoastalBaffa 7173 Shield Massif 7105 7021 7121 Benue 7136 6°N

Gulf of Guinea 7183 Niger Delta 7192

Base from U.S. Geological Survey digital data, 2002 Zaire West Zaire 7225 World Geodetic System 1984 (WGS 84) 0° Prime Meridian, Greenwich, 0° Precambrian Belt 7211

0 300 600 KILOMETERS

0 300 600 MILES West-Central 6°S Coastal 7203 EXPLANATION ATLANTIC OCEAN Quaternary

Quaternary and Tertiary

Tertiary 12°S

Cretaceous

Triassic and Jurassic

Paleozoic

Precambrian Etosha 18°S 7285 Igneous

Salt structure Contact Damer Belt Niger Delta Province boundary Walvis Ridge 7311 Other petroleum province boundary Kalahari Baffa Petroleum province identifier 24°S 7325 7105

Orange River Coastal 30°S 7303 Karoo 7355

South African Coastal 36°S 7363

Geology by Persits and others, 2002 Figure 3. Generalized geology of west Africa (Persits and others, 2002), petroleum province boundaries, and 20 province names and codes as defined by Klett and others (1997).

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch05_figures\ch05_figures\ch05_figure03.ai Introduction 5

8°W 4°W 0° 4°E 8°E Volta 7035 7114 Iullemmeden 7055

Volta Basin Nigerian Massif 7121 8°N West African Dahomey Embayment Shield Benue 7021 7136

Ivory Coast Basin

West African Coastal 7173 Gulf of Guinea 7183 4°N Niger Delta 7192

Gulf of Guinea

West Zaire ATLANTIC OCEAN Precambrian West-Central Belt Coastal 7211 7203

0°

Base from U.S. Geological Survey digital data, 2002 0 100 200 KILOMETERS Geology modified from Persits and others, 2002 World Geodetic System 1984 (WGS 84) Prime Meridian, Greenwich, 0° 0 100 200 MILES

EXPLANATION

Quaternary Paleozoic and Mesozoic Contact Niger Delta Province boundary Pleistocene Paleozoic Other petroleum province Quaternary and Tertiary Precambrian boundary Niger Delta Petroleum province identifier Tertiary Igneous 7192

Cretaceous—Undivided Salt structure

Lower Cretaceous

Figure 4. Geology of the Gulf of Guinea and the Niger Delta, Africa, showing 11 provinces.

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch05_figures\ch05_figures\ch05_figure04.ai 6 Assessment of Undiscovered Oil and Gas Resources of the Niger Delta Province, Nigeria and Cameroon, Africa Geology of the of the Niger Delta 1997). Shallow marine clastic sediment was deposited farther offshore and, in the Anambra basin (fig. 1), is represented Province, Nigeria and Cameroon, by the Albian-Cenomanian Asu River shale, Cenomanian- Santonian Eze Aku and Awgu shales (fig. 7), and Campanian Africa to Maastrichtian Nkporo shale (fig. 8), among others (Reijers and others, 1997). The distribution of Late Cretaceous shale Tectonics beneath the Niger Delta is unknown. In the Paleocene, a major transgression began with The tectonic framework of the continental margin deposition of the Imo shale in the Anambra Basin to the along the West Coast of equatorial Africa is controlled by northeast and the Akata shale in the Niger Delta Basin area to Cretaceous fracture zones expressed as trenches and ridges the southwest (fig. 8). In the Eocene, the delta coastline was in the deep Atlantic. The fracture-zone ridges subdivide the again influenced by longshore currents, and wave-dominated west African margin into individual basins and, in Nigeria, sedimentation predominated (Burke, 1972; Reijers and others, form the boundary faults of the Cretaceous Benue-Abakaliki 1997). At this time, deposition of paralic sediment began in Trough (figs. 1, 2), which extends eastward into the west the Niger Delta Basin proper and, as the sediment prograded African shield. The trough represents a failed arm of a south, the coastline became progressively more convex triple junction associated with the opening of the South seaward. Today, deltaic sedimentation is still wave dominated. Atlantic. In this part of the Africa and South America The Tertiary section of the Niger Delta is divided into continental margins, rifting started in the Early Cretaceous and three formations, representing prograding depositional facies persisted into the Late Cretaceous (Genik, 1993). In the Niger (figs. 7, 8, 9). These formations are the Akata Formation, Delta area, rifting ended in the latest Cretaceous. Figure 5 the Agbada Formation, and the Benin Formation. The shows Early Cretaceous to Holocene paleogeography of three formations were deposited during offlapping clastic- west-central Africa and South America. After rifting ceased, sedimentation cycles that compose the Niger Delta. The gravity tectonism became the primary deformational process. deposits resulting from these cycles (“depobelts”) are Shale mobility induced internal deformation and occurred 30–60 km wide and prograde southwestward 250 km in response to two processes (Kulke, 1995). First, loading over oceanic crust into the Gulf of Guinea (fig. 10) by higher density delta-front sands in the overlying Agbada (Whiteman, 1982; Stacher, 1995). They are characterized by Formation induced shale diapirs to form in the underlying synsedimentary listric faulting in response to variable rates poorly compacted and overpressured prodelta and delta-slope of subsidence and sediment supply (Doust and Omatsola, clays of the Akata Formation. Second, a lack of basinward 1990). The interaction of subsidence and supply rates resulted support from the under-compacted delta-slope clays of the in sedimentation in the depobelts, and when further crustal Akata Formation led to slope instability within the delta subsidence of the basin could no longer be accommodated, complex. Gravity tectonics, which ended before deposition of the focus of sediment deposition shifted seaward and formed the Benin Formation, are expressed in complex structures such a new depobelt (Whiteman, 1982; Doust and Omatsola, as shale diapirs, roll-over anticlines, collapsed growth faults, 1990). Five major depobelts are generally recognized, each back-to-back features, and steeply dipping, closely spaced with its own sedimentation, deformation, and petroleum flank faults (Doust and Omatsola, 1990; Stacher, 1995). history (Doust and Omatsola, 1990; Tuttle, Brownfield, and Charpentier, 1999). The shorelines shown in figure 10 Depositional History approximate the depobelt shorelines described by Doust and Omatsola (1990). The Cretaceous section has not been penetrated The type sections for these formations are described beneath the Niger Delta Basin, the youngest and southern- in Short and Stäuble (1967) and summarized in a variety most subbasin in the Benue-Abakaliki Trough (figs. 1, 6). of papers (for example, Doust and Omatola, 1990; Kulke, Cretaceous rocks deposited in what is now the Niger Delta 1995). The Akata Formation at the base of the delta is Basin can be extrapolated only from an exposed Cretaceous of marine origin and is composed of thick shale sections section in the next basin to the northeast—the Anambra containing potential source rock and turbidite-sand reservoirs Basin (fig. 1). From the Campanian through the Paleocene, in the deeper parts of the delta (figs. 7, 9). Beginning in longshore drift along a shoreline that was concave into the the Paleocene and continuing to the Holocene, the Akata Anambra Basin resulted in tide-dominated deltaic sedimenta- Formation accreted, during lowstands, when terrestrial tion during transgressions and river-dominated sedimenta- organic matter and clays were transported to deep-water tion during regressions (Burke, 1972; Reijers and others, areas of the delta. Only the upper part of the formation has Geology of the of the Niger Delta Province, Nigeria and Cameroon, Africa 7

A. 126 million years ago, Neocomian B. 108 million years ago, late Aptian

ARABIA ARABIA

SOUTH SOUTH AMERICA AFRICA AMERICA AFRICA

INDIAN INDIAN OCEAN OCEAN

C. 96 million years ago, late Albian D. 90–84 million years ago, Turonian - Santonian ARABIA ARABIA

AFRICA SOUTH AMERICA ATLANTIC ATLANTIC SOUTH

AFRICA INDIAN INDIAN OCEAN AMERICA OCEAN

E. 74 million years ago, late Campanian F. 54 million years ago, early Eocene ARABIA ARABIA

AFRICA AFRICA ATLANTIC ATLANTIC SOUTH

AMERICA INDIAN OCEAN

G. 30–0 million years ago, Miocene to recent ARABIA

RED SEA EXPLANATION Continental sediment Incipient rift—Longer dash where ±10 million years younger Marine transgression with marine deposition Adamawa uplift Gulf of Guinea Province system boundary Direction of active extension Major fault or block boundary— AFRICA Dashed where uncertain Direction of possible compression Strike-slip fault—Arrows show ATLANTIC sense of movement Direction of marine incursion Contact—Dashed where uncertain Area of Paleogene rifting

INDIAN OCEAN

Figure 5. Paleotectonic maps showing evolution of the west Africa and South America continental margins. Niger Delta Province outlined in red. Modified from Genik (1993).

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch05_figures\ch05_figures\ch05_figure05.ai 8 Assessment of Undiscovered Oil and Gas Resources of the Niger Delta Province, Nigeria and Cameroon, Africa

A 5°E 10°E

Benue Trough B' 2 Dahomey Embayment 3 2 4 3 5 A 8 6 4 5°N

B 10 8 A' Chain 6 5 Fault Zone 4

3

Charcot Fault Zone

Cameroon Volcanic Line 0° 0 50 100 KILOMETERS

0 50 100 MILES

EXPLANATION Fault Scarp on fault—Hachures point downscarp A A' Line of section 3 Isopach contour—Thickness in kilometers. Contour interval varies

B WEST EAST A A'

Cenozoic

Romanche Fault Zone

Upper Cretaceous

Basement complex Lower Cretaceous

Jurassic (?) Line Cameroon Volcanic Chain Fault Zone Charcot Fault Zone

NOT TO SCALE Figure 6. A, Isopach map of Niger Delta; isopachs represent total sediment thickness (Kaplan and others, 1994). B, Diagrammatic west- east cross section through the Niger Delta region. Modified from Whiteman (1982).

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch05_figures\ch05_figures\ch05_figure06.ai Petroleum Occurrence in the Niger Delta Province, Nigeria and Cameroon, Africa 9

Present-day Niger Delta Province SOUTH NORTH delta front boundary B B' METERS Sea level Miocene-Pliocene Benin facies Coal facies 1,000 delta front Agabada 2,000 Reservoirs Eocene delta front 3,000 Assessment Miocene Awgu Shale Unit delta front Agabada Reservoirs 4,000 Oligocene Eze Aku Group Agabada Reservoirs delta front Assessment Unit Paleocene– Asu 5,000 Assessment Unit Upper Cretaceous River Group delta front 6,000

7,000 Akata Reservoirs 8,000 Akata Reservoirs crust Assessment inental Assessment Unit Cont 9,000 Unit Limit uncertain 10,000

Aeromagnetic Oceanic crust basement 11,000 meters

0 100 200 KILOMETERS

0 100 200 MILES

EXPLANATION

Continental facies

Marine facies

Basement complex—Oceanic and continental Contact—Dashed where uncertain Facies boundary

Unconformity Figure 7. Southwest-northeast cross section (B–B ’ in fig. 6A) through the Niger Delta region. Modified from Whiteman (1982). been drilled. It is estimated that the formation is as much as Petroleum Occurrence in the Niger 7,000 m thick (Doust and Omatsola, 1990). The formation underlies the entire delta, and it is typically overpressured. Delta Province, Nigeria and Cameroon, Turbidity currents likely deposited deep-sea fan sands within the upper Akata Formation during development of the delta. Africa Deposition of the overlying Agbada Formation began in the Eocene and continues into the Holocene (figs. 7, 9). The Oil and gas occur throughout the Agbada Formation formation consists of marine, marginal-marine, and nonmarine of the Niger Delta (figs. 1, 2), however, several oil-and-gas- siliciclastic units more than 3,700 m thick that represent the field trends form an oil-rich belt having the largest fields and deltaic portion of the succession (fig. 9). Clastic sediment lowest gas:oil ratios. The belt extends from the northwest accumulated in delta-front and fluviodeltaic environments. In offshore area to the southeast offshore and along a number the lower Agbada Formation, shale and sandstone beds were of north-south trends near (Tuttle, Brownfield, deposited in equal proportions; however, the upper portion is and Charpentier, 1999, fig. 1). The trend corresponds to mostly sandstone with only minor shale interbeds. The Agbada the transition between continental and oceanic crust and is Formation is overlain by the Benin Formation, a latest Eocene within the axis of maximum sedimentary thickness (fig. 6). to Holocene deposit of alluvial and upper coastal plain sands Stacher (1995), using sequence stratigraphy, developed a that are as much as 2,000 m thick (fig. 7). hydrocarbon-habitat model for the Niger Delta (fig. 11). The 10 Assessment of Undiscovered Oil and Gas Resources of the Niger Delta Province, Nigeria and Cameroon, Africa

WEST EAST Age Niger Delta Basin Anambra Basin Millions of Stage

years ago Epoch 40 Bartonian Sequence boundary Lutecian

Agbada Formation Nanka Formation

50 Eocene

Ypresian Ameki Formation

Thanetian 60 Imo Formation Maximum flooding surface Formation Danian Paleocene Akata Formation Maastrichtian Ajali Formation 70 Mamu Formation Sequence boundary Mamu Formation Campanian Owelli Sandstone Shale Nkporo Shale Maximum flooding surface 80 Santonian Sequence boundary? Awgu Formation Maximum flooding surface? Late Cretaceous Sequence boundary Coniacian

90 NOT TO SCALE EXPLANATION Coal Channel Tidal structure Contact Figure 8. Stratigraphic section of the Anambra Basin (fig. 1) from Late Cretaceous through Eocene and time-equivalent formations in the Niger Delta Basin. Modified from Reijers and others (1997).

model was constructed for the central portion of the delta, Source Rocks including some of the oil-rich belt, and relates deposition of the Akata Formation (assumed lowstand source rock) and Several reports have debated the source rock for oil the sand-shale units in the Agbada Formation (the reservoirs and gas within the Niger Delta (Ekweozor and Okoye, 1980; and seals) to sea level. The Akata Formation shale, which Lambert-Aikhionbare and Ibe, 1984; Bustin, 1988; Doust and was deposited in deep water during lowstands, is overlain by Omatsola, 1990; Tuttle, Brownfield, and Charpentier, 1999; the Agbada sequences. The Agbada Formation in the central Haack and others, 2000). Source rocks include the interbedded portion of the delta fits a shallow-ramp model with mainly marine shale in the Agbada Formation, the marine Akata shale, highstand (hydrocarbon-bearing sandstone) and transgres- and possibly Cretaceous shale (Ekweozor and Okoye, 1980; sive (sealing shale) system tracts. Faulting in the Agbada Lambert-Aikhionbare and Ibe, 1984; Doust and Omatsola, Formation provided pathways for petroleum migration and \\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch05_figures\ch05_figures\ch05_figure08.ai1990; Stacher, 1995; Tuttle, Brownfield, and Charpentier, formed structural traps that, together with stratigraphic traps, accumulated hydrocarbons. The shale in the transgressive 1999; Haack and others, 2000). system tract provided an excellent seal above the sand as well Some intervals in the Agbada Formation contain organic as enhancing clay smearing within fault zones. carbon contents sufficient to be considered good source The Akata Formation underlies the entire Niger Delta rocks (Ekweozor and Okoye, 1980). The source-rock intervals Province (figs. 1, 2). It contains hydrocarbons within rarely reach thicknesses sufficient to produce a world-class oil sandstone-units-related growth-fault structures, rotated fault province and are immature in parts of the delta (Stacher, 1995). blocks within the lower parts of the continental shelf, and The Akata shale is present in large volumes beneath the Agbada stratigraphic traps related to turbidites. The turbidites include Formation (fig. 7) and is at least volumetrically sufficient to channel and ponded sandstone and deep-water clastic fans in generate enough oil for a world-class oil province such as the the deep-water part of the Niger Delta. Niger Delta (Klett and others, 1997). Petroleum Occurrence in the Niger Delta Province, Nigeria and Cameroon, Africa 11

SOUTHWEST NORTHEAST Quaternary Deltaic facies Pliocene (Agbada Formation) Continental alluvial sand (Benin Formation)

Late

Afam Clay Marine shale

Soku Clay Middle Deltaic facies Miocene Buguma Clay

Agbada Clay Opuama channel Early complex (Agbada Formation) Marine shale Marine shale (Akata Formation) Oligocene

Deltaic facies Late

Middle Eocene

Early

Paleocene

Late Cret AB-TU NOT TO SCALE EXPLANATION

Extent of erosional truncation Contact Extent of erosional truncation boundary Cret Cretaceous AB-TU Albian-Turonian Figure 9. Schematic cross section of the Niger Delta, Africa. Eocene Agbada Formation contains deltaic- sandstone reservoirs and traps. Akata Formation contains turbidite sandstone and lowstand channels, sheet sands, and fans. Modified from Shannon and Naylor (1989) and Doust and Omatsola (1990).

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch05_figures\ch05_figures\ch05_figure09.ai 12 Assessment of Undiscovered Oil and Gas Resources of the Niger Delta Province, Nigeria and Cameroon, Africa

Some authors have proposed that oil-bearing Cretaceous rocks may be beneath and east of the present Niger Delta (Frost, 1997; Haack and others, 2000). This Cretaceous section has not been drilled owing to its great depth; therefore, no data exist on its source-rock potential. Migration of oil from the Cretaceous into reservoirs in the Agbada Formation would Upp er Eoc ene require an intricate fault or fracture network, because the Akata O lig oc e ne shale reaches a thickness greater than 6,000 m. No data exist to support the existence of such a network. Haack and others M iocene (2000) reported rocks and marine kerogen may be present along the Nigerian coastline and offshore. These conclusions are ATLANTIC based on oil seeps from Nigerian tar sands within the Dahomey OCEAN Pre M sent io ne Embayment (fig. 4), source-rock outcrops along the eastern cene-Plioce Pli margin of the delta, and geochemical data from wells. These ocene-Pleistocene source rocks could be contributors to hydrocarbon accumula- 0 30 60 KILOMETERS tions in the deep-water areas of the Niger Delta. 0 30 60 MILES In the northwestern part of the Niger Delta, the oil window lies in the upper Akata Formation and the lower EXPLANATION Agbada Formation (fig. 12). To the southeast, the oil window Cretaceous and younger is stratigraphically lower, as much as 4,000 ft below the sediment upper Akata–lower Agbada strata (Evamy and others, 1978). Pre-Cretaceous basement The present day oil-generation window in the Niger Delta is Approximate coastline positions approximately at the 240 °F (115 °C) isotherm. at the designated time—Dashed A burial history chart for the Oben-1 well (fig. 12) in where uncertain the northern part of the Niger Delta is shown in figure 13. Lower Tertiary basin axis and direction of clastic supply The Akata-Agbada Formation boundary entered the oil

window at approximately 0.6 percent Ro in the late Eocene. The Figure 10. Coastline progradation of the Niger Delta since Akata-Agbada boundary in this part of the delta is currently at a 35 million years ago (Ma). The delta has advanced seaward more depth of about 4,300 m, with the upper Akata Formation in the than 200 kilometers and has broadened from a width of less than wet-gas-condensate generating zone (vitrinite reflectance greater 300 kilometers to a width of about 500 kilometers. Shorelines than 1.2 percent; Tissot and Welte, 1984). The lowermost part approximate the Doust and Omatsola (1990) depobelts. Modified of the Agbada Formation entered the oil-generation window from Whiteman (1982). sometime in the late Oligocene. Bustin (1988) reported total organic carbon (TOC) analyses of Agbada Formation siltstone and shale samples Reservoirs to be essentially the same, averaging 1.4 to 1.6 weight Oil and gas in the Agbada Reservoirs AU is produced from percent. The TOC content, however, seems to vary with sandstone and unconsolidated sand primarily found within the age of the strata—an average of 2.2 weight percent in the Agbada Formation (fig. 9). Known reservoir rocks are Eocene to late Eocene compared to 0.9 weight percent in Pliocene Pliocene in age, are commonly stacked, and range in thickness strata. Bustin (1988) reported that the Eocene TOC average from less than 15 m to greater than 45 m (Evamy and others, compares well with the averages of 2.5 weight percent and 1978). The thicker reservoirs likely represent amalgamated 2.3 weight percent obtained for Agbada-Akata shales in two bodies of stacked channels (Doust and Omatsola, 1990). Based wells (Udo and Ekweozor, 1988). Ekweozor and Okoye on reservoir geometry and quality, Kulke (1995) described the (1980) reported TOC values ranging from 0.4 to 14.4 weight most important reservoir types as point bars of distributary \\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch05_figures\ch05_figures\ch05_figure10.ai percent in the both onshore and offshore paralic sediments. channels and coastal barrier bars intermittently cut by sand-filled channels. Edwards and Santogrossi (1990) described the primary Nwachukwu and Chukwura (1986) reported values as high Niger Delta reservoirs as Miocene sandstones with as much as as 5.2 weight percent in paralic shales from the western part 40 percent porosity, 2 darcies permeability, and a thickness of of the delta. Bustin (1988) concluded that there are no rich 100 m. The variation in reservoir thickness is strongly controlled source rocks in the delta and that the poor quality of the by growth faults; the sandstone thickens against the fault within source rock has been partly offset by its great volume and the down-thrown block (Weber and Daukoru, 1975). Porosity excellent migration pathways. The oil potential is further typically decreases with depth (Kulke, 1995). increased by permeable interbedded sandstone and rapid Computer modeling suggests that local fault movements hydrocarbon generation and overpressuring resulting from along the shelf edge control the thickness and lithofacies of high sedimentation rates. potential reservoir sand downdip (Tuttle, Brownfield, and Petroleum Occurrence in the Niger Delta Province, Nigeria and Cameroon, Africa 13

SOUTH NORTH

Transgression

Highstand Transgression (shallow ramp) Agbada Formation Highstand

Transgression (lowstand) Akata Formation

NOT TO SCALE

EXPLANATION

Hydrocarbon accumulation Flooding surface Main boundary fault Hydrocarbon migration path Fault Principal source rock Top of oil window Contributing source rock

Figure 11. Sequence-stratigraphic model for the central portion of the Niger Delta. Source rock, migration pathways, and hydrocarbon traps mainly related to growth faults, but minor stratigraphic traps present. Hydrocarbon fluids migrated laterally through Agbada Formation sandstone units. The main boundary fault separates megastructures, which represent major breaks in the regional dip of the delta (Evamy and others, 1978). Modified from Stacher (1995).

Charpentier, 1999; their figure 15). The slope-edge fault and In the deep-water part of the delta, the primary reservoirs reservoir simulation from these experiments are shown in found in Akata Reservoirs AU are mostly stratigraphic and figure 14. include turbidite sands, lowstand sand bodies, and clastic fans (Beka and Oti, 1995). Structural traps are less common in the Traps and Seals deep-water parts of the delta. The major reservoir seal rocks in the Niger Delta Traps in Niger Delta oil and gas fields are mostly are interbedded shale units within the Agbada and Akata structural, although stratigraphic traps are not uncommon formations. The shale provides three types of seals in the (fig. 15). Structural traps developed during synsedimentary Agbada: clay smears along faults, interbedded strata against deformation of the Agbada paralic sequences (Evamy and which reservoir sands are juxtaposed due to faulting, and others, 1978; Stacher, 1995). Structural complexity increases vertical seals (Doust and Omatsola, 1990). On the flanks of the from north to south within the depobelts in response to delta, major erosional events of early to middle Miocene age increasing instability of the less-compacted, overpressured shale. Doust and Omatsola (1990) described a variety of formed canyons that are now clay filled (fig. 9). These clays structural-trapping elements, including those associated with form the top reservoir seals for some highly productive(?) simple rollover structures, clay-filled channels, structures with offshore fields (Doust and Omatsola, 1990). Akata shale is multiple growth faults, structures with antithetic faults, and the primary seal in the deep-water parts of the delta where collapsed-crest structures (fig. 15). turbidites and submarine fans are the primary traps. 14 Assessment of Undiscovered Oil and Gas Resources of the Niger Delta Province, Nigeria and Cameroon, Africa

5°E 6°E 7°E 8°E

6°N Oben-1 12,000 13,000

11,000 NIGERIA

14,000

14,000

5°N

Port Harcourt 14,000 13,000

12,000 11,000

13,000 14,000 12,000

ATLANTIC 10,000 OCEAN 11,000 4°N

0 25 50 KILOMETERS

0 25 50 MILES

EXPLANATION

Top of oil kitchen in lower 10,000 Depth contour to top of oil Agbada Formation kitchen (240 ºF, 115 ºC)— Contour is in feet. Contour Top of oil kitchen in interval 1,000 feet Akata Formation Oben-1 Well and identifier

Figure 12. Subsurface depth to top of Niger Delta oil kitchen showing that the entire Akata Formation and a portion of the lower Agbada Formation are in the oil window. Modified from Evamy and others (1978).

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch05_figures\ch05_figures\ch05_figure12.ai Petroleum Occurrence in the Niger Delta Province, Nigeria and Cameroon, Africa 15

GEOLOGIC TIME 60 50 40 30 20 10 SCALE Age in million years (Ma) Cenozoic Tertiary ROCK Oligocene Plio to Eocene Miocene present UNIT

Akata Formation Agbada Formation Benin Formation DEPTH (kilometers)

1

2

Agbada Formation Ro = 0.6

3 Ro = 0.8

Ro = 1.2 4

5 Ro = 2.0

Akata Formation 6

7 Activation of Northern Depobelt

EXPLANATION Actual burial curve Projected burial curve Isoreflectance line

Ro Vitrinite reflectance Figure 13. Burial-history chart for the northern portion of the Tertiary Niger Delta (Akata-Agbada). Data from Oben-1 well (fig. 12) in northern depobelt (Doust and Omatsola (1990). Modified from Ekweozor and Daukoru (1994). Plio, Pliocene.

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch05_figures\ch05_figures\ch05_figure13.ai 16 Assessment of Undiscovered Oil and Gas Resources of the Niger Delta Province, Nigeria and Cameroon, Africa

Shoreward Basinward Distance in kilometers 0 10 20 30 40 50

METERS Sea level Slope Edge 250

500

750

1,000

1,250

1,500

1,750 Slope-edge normal faults 2,000

2,250

2,500

2,750

3,000

0 5 10 KILOMETERS

0 5 10 MILES

VERTICAL GREATLY EXAGGERATED Figure 14. Slope edge normal-fault simulation (2 million years ago (Ma) to present) of the Niger Delta. Orange and yellow, potential hydrocarbon accumulations in sandstone reservoirs. Figure provided by Linda Smith-Rouch (written commun., 1998; Tuttle, Brownfield, and Charpentier, 1999).

Exploration Geologic Model

Between the USGS World Assessment 2000 The geologic model developed for the assessment of (U.S. Geological Survey World Energy Assessment Team, conventional oil and gas in the Niger Delta Province and the 2000) and this assessment (2009), both the Agbada and the Coastal Plain and Offshore AU is as follows: Akata Reservoirs AUs added fields. The Agbada added 84 oil 1. The primary source rock for petroleum is the upper fields and 22 gas fields exceeding the minimum assessment Akata Formation, the marine-shale facies of the delta. size of 1 million barrels of oil equivalent (MMBOE). It now Additional hydrocarbon contributions from interbed- contains a total of 537 oil and 161 gas fields. The Akata ded marine shale of the lowermost Agbada Formation Reservoirs AU added 39 new oil fields and 13 new gas are possible. Oil and gas were generated from Eocene \\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch05_figures\ch05_figures\ch05_figure14.aifields—the total number of fields in the assessment unit— paralic and prodeltic Type II and Type III kerogen exceeding the minimum assessment size of 5 MMBOE. In the ranging from 1.4 weight percent to 5.2 weight percent Agbada Reservoirs AU, the largest grown oil field is about total organic carbon and possibly from Cretaceous 2.0 BBO and the largest grown gas field is about 8.2 TCF. In marine and lacustrine sources. Hydrocarbon the Akata Reservoirs AU, the largest grown oil field is about generation began in the Eocene and continues to 1.4 BBO and the largest grown gas field is 8.5 TCF. The the present. Petroleum generation shifted north to Niger Delta Province is considered mature on the basis of its south as progressively younger depobelts entered the exploration activity. oil window. Producing fields (IHS Energy, 2008) provide evidence for two inferences: the existence of an active petroleum 2. Petroleum migrated into Eocene Agbada Formation system containing Tertiary source rocks that have produced sandstone reservoirs and traps. Petroleum also migrated hydrocarbons most likely since the Eocene, and the migration into Akata Formation turbidite sandstone units including of hydrocarbons into Tertiary reservoirs. lowstand channels, sheet sands, and fans. Geologic Model 17

Simple rollover structure with clay-filled channel Structure with multiple growth faults SOUTH NORTH SOUTH NORTH Growth fault Stratigraphic Growth fault trap Clay filled channel Rollover structure

Rollover structure Stratigraphic trap Fault closures

Fault closure Stratigraphic trap

Rollover structure Sand pinchout Stratigraphic trap

Sand pinchout Akata Akata

NOT TO SCALE NOT TO SCALE

Structure with antithetic fault Collapsed-crest structure

SOUTH NORTH SOUTH NORTH Antithetic fault Growth fault Rollover structure Antithetic fault Growth faults Collapsed crest Fault closure

Fault closures Fault closures Rollover structure

Akata Akata

NOT TO SCALE NOT TO SCALE

EXPLANATION Strike-slip fault—Arrows show sense of movement Inferred bedding surface Figure 15. Oil field structures and associated trap types, Niger Delta, Nigeria and Cameroon, Africa. Modified from Doust and Omatsola (1990) and Stacher (1995).

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch05_figures\ch05_figures\ch05_figure15.ai 18 Assessment of Undiscovered Oil and Gas Resources of the Niger Delta Province, Nigeria and Cameroon, Africa

3. Traps are mostly structural in the Agbada Reservoirs AU, PETROLEUM but stratigraphic traps are also present. Turbidite traps are SYSTEM EVENTS the major trapping style in the Akata Reservoirs AU. 4. The Eocene marine mudstone and shale rocks are the

primary reservoir seals in both Agbada and Akata ACCUMULATION

assessment units. 5. The Niger Delta is considered mature for oil and gas; MIGRATION- therefore, current field histories were used in part to determine the distributions of sizes and numbers of

undiscovered fields. GENRATION- ROCK UNIT RESERVOIR ROCK

OVERBURDEN ROCK PRESERVATION Age in million years (Ma) SOURCE ROCK SEAL ROCK TRAP FORMATION An events chart (fig. 16) for the Tertiary Niger Delta 0 Plio Total Petroleum System and the Agbada Reservoirs and Neogene Akata Reservoirs AUs summarizes the age of the source, Mio 24 seal, and reservoir rocks and the timing of trap development, Olig generation, and migration of petroleum. Paleogene Eoc 50 Resource Summary Pal 65 The USGS estimated mean volumes of undiscovered, technically recoverable conventional oil and gas resources for L the Agbada Reservoirs Assessment Unit in the Niger Delta Cretaceous Province (table 1) at 1,616 million barrels of oil, 9,454 billion 100 cubic feet of gas, and 494 million barrels of natural gas liquids. The estimated mean size of the largest oil field that is expected E to be discovered is 274 million barrels of oil, and the estimated mean size of the expected largest gas field is 981 billion cubic feet of gas. The estimated mean volumes for the Akata 146 Reservoirs Assessment Unit (table 1) are 13,918 million barrels 150 L of oil, 48,767 billion cubic feet of gas, and 5,832 million barrels of natural gas liquids with estimated mean sizes of the largest oil M and gas fields of 4,119 million barrels of oil and 13,355 billion Jurassic cubic feet of gas, respectively. For this assessment, a minimum undiscovered field size of 1 million barrels of oil equivalent was E used for the Agbada Reservoirs Assessment Unit and a minimum 200 200 undiscovered field size of 5 million barrels of oil equivalent was used for the Akata Reservoirs Assessment Unit. No attempt was L made to estimate economically recoverable reserves. Triassic M E For Additional Information 250 251 L Permian Assessment results are available at the USGS Central E Energy Resources Science Center website: http://energy.cr.usgs. gov/oilgas/noga/ or contact Michael E. Brownfield, the assessing Figure 16. Events chart for the Tertiary Niger Delta Total Petroleum geologist ([email protected]). System (719201) and the Agbada and Akata Reservoirs Assessment Units (71920101; 71920102) in the Niger Delta Province, Africa. Gray, Acknowledgments rock units present; yellow, age range of reservoir rock; green, age ranges of source, seal, and overburden rocks and the timing The author wishes to thank Mary-Margaret Coates, of trap formation and generation, migration, and preservation Jennifer Eoff, Christopher Schenk, and David Scott for their of hydrocarbons; wavy line, unconformity. Divisions of geologic suggestions, comments, and editorial reviews, which greatly improved the manuscript. The author thanks Wayne Husband time conform to dates in U.S. Geological Survey Geologic Names for his numerous hours drafting many of the figures used Committee (2010). Ma, million years ago; Plio, Pliocene; Mio, in this manuscript, and Chris Anderson,\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch05_figures\ch05_figures\ch05_figure16.ai who supplied the Miocene; Olig, Oligocene; Eoc, Eocene; Pal, Paleocene, L, Late; E, Geographic Information­ System files for this assessment. Early; M, Middle; ?, uncertain. References 19

Table 1. Niger Delta Province and Agbada and Akata Reservoirs Assessment Units results for undiscovered, technically recoverable oil, gas, and natural gas liquids.

[Largest expected mean field size in million barrels of oil and billion cubic feet of gas; MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked estimates. For gas accumulations, all liquids are included as natural gas liquids (NGL). Undiscovered gas resources are the sum of nonassociated and associated gas. F95 represents a 95-percent chance of at least the amount tabulated; other fractiles are defined similarly. Fractiles are additive under assumption of perfect positive correlation. AU, assessment unit; AU probability is the chance of at least one accumulation of minimum size within the AU. TPS, total petroleum system. Fractiles are additive under assumption of perfect positive correlation. Gray shading indicates not applicable]

Largest Total undiscovered resources Province, Field expected Oil (MMBO) Gas (BCFG) NGL (MMBNGL) Total Petroleum Systems (TPS) type mean field and Assessment Units (AU) F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean size Niger Delta Province—Tertiary Niger Delta TPS Oil 274 526 1,437 3,326 1,616 1,904 5,387 13,011 6,139 65 245 904 339 Agbada Reservoirs AU Gas 981 751 2,742 7,817 3,315 30 120 397 155 Oil 4,119 4,321 12,271 29,129 13,918 5,432 16,270 45,864 19,779 143 433 1,253 535 Akata Reservoirs AU Gas 13,355 5,862 21,723 78,443 28,988 1,030 3,886 14,491 5,297 Total Conventional Resources 4,847 13,708 154,081 15,534 8,949 46,122 145,135 58,221 1,268 4,684 17,045 6,326

References Frost, B.R., 1997, A Cretaceous Niger Delta petroleum system, in Extended abstracts, American Association of Petroleum Beka, F.T., and Oti, M.N., 1995, The distal offshore Niger Geologists Bulletin/Brazilian Association of Petroleum Delta—Frontier prospects of a mature petroleum province, in Geologists Hedberg Research Symposium, Petroleum Sys- Oti, M.N., and Postma, G., eds., Geology of deltas: Rotterdam, tem of the South Atlantic Margin, November 16–19, 1997, A.A. Balkema, p. 237–241. Rio de Janeiro, Brazil. Burke, K., 1972, Longshore drift, submarine canyons, and sub- Genik, G.J., 1993, Petroleum geology of the Cretaceous- marine fans in development of Niger Delta: American Associa- Tertiary basins in Niger, Chad, and Central African tion of Petroleum Geologists Bulletin, v. 56, p. 1975–1983. Republic: American Association of Petroleum Geologists Bustin, R.M., 1988, Sedimentology and characteristics of Bulletin, v. 73, no. 8, p. 153–168. dispersed organic matter in Tertiary Niger Delta—Origin of Haack, R.C., Sundararaman, P., Diedjomahor, J.O., Xiao, H., source rocks in a deltaic environment: American Associa- Gant, N.J., May, E.D., and Kelsch, K., 2000, Niger Delta tion of Petroleum Geologists Bulletin, v. 72, p. 277–298. petroleum systems, Nigeria, in Mello, M.R., and Katz, Doust, Harry, and Omatsola, Ebi, 1990, Niger Delta, in B.J., eds., Petroleum systems of South Atlantic margins: Edwards, J.D., and Santogrossi, P.A., eds., divergent/passive American Association of Petroleum Geologists Memoir 73, margin basins, American Association of Petroleum Geolo- p. 213–231. gists Memoir 48: Tulsa, American Association of Petroleum IHS Energy, 2008, International petroleum exploration and pro- Geologists, p. 201–238. duction database [current through December 2008]: Available Edwards, J.D., and Santogrossi, P.A., 1990, Summary and from IHS Energy, 15 Inverness Way East, Englewood, CO conclusions, in Edwards, J.D., and Santogrossi, P.A., eds., 80112 USA. Divergent/passive margin basins: American Association of Petroleum Geologists Memoir 48, p. 239–248. Kaplan, A., Lusser, C.U., and Norton, I.O., 1994, Tectonic map of the world, panel 10: Tulsa, American Association of Petro- Ekweozor, C.M., and Daukoru, E.M., 1994, Northern delta leum Geologists, scale 1:10,000,000. depobelt portion of the Akata-Agbada(!) petroleum system, Niger Delta, Nigeria, in Magoon, L.B., and Dow, Klett, T.R., Ahlbrandt, T.A., Schmoker, J.W., and Dolton, G.L., W.G., eds., The petroleum system—From source to trap: 1997, Ranking of the world’s oil and gas provinces by known American Association of Petroleum Geologists Memoir 60, petroleum volumes: U.S. Geological Survey Open-File p. 599–614. Report 97–463, CD–ROM. Ekweozor, C.M., and Okoye, N.V., 1980, Petroleum source- Kulke, H., 1995, Nigeria, in Kulke, H., ed., Regional petroleum bed evaluation of Tertiary Niger Delta: American Associa- geology of the world. Part II—Africa, America, Australia and tion of Petroleum Geologists Bulletin, v. 64, p. 1251–1259. Antarctica: Berlin, Gebrüder Borntraeger, p. 143–172. Evamy, B.D., Haremboure, J., Kamerling, P., Knaap, W.A., Lambert-Aikhionbare, D.O., and Ibe, A.C., 1984, Petroleum Molloy, F.A., and Rowlands, P.H., 1978, Hydrocarbon source-bed evaluation of the Tertiary Niger Delta— habitat of Tertiary Niger Delta: American Association of Discussion: American Association of Petroleum Geologists Petroleum Geologists Bulletin, v. 62, p. 277–298. Bulletin, v. 68, p. 387–394. 20 Assessment of Undiscovered Oil and Gas Resources of the Niger Delta Province, Nigeria and Cameroon, Africa

Nwachukwu, J.I., and Chukwura, P.I., 1986, Organic matter Tuttle, M.L., Charpentier, R.R., and Brownfield, M.E., 1999, of Agbada Formation, Niger Delta, Nigeria: American Asso- Assessment of undiscovered petroleum in the Tertiary Niger ciation of Petroleum Geologists Bulletin, v. 70, p. 48–55. Delta (Akata-Agbada) Petroleum System (719201), Niger Delta Province, Nigeria, Cameroon, and Equatorial Guinea, Persits, F.M., Ahlbrandt, T.S., Tuttle, M.L., Charpentier, R.R., Africa, in Tuttle, M.L., Charpentier, R.R., and Brownfield, Brownfield, M.E., and Takahashi, K.I., 2002, Map showing M.E., eds., The Niger Delta Petroleum System, Niger Delta geology, oil and gas fields, and geologic provinces of Africa: Province, Nigeria, Cameroon, and Equatorial Guinea, U.S. Geological Survey Open-File Report 97–470A, Ver- Africa: U.S. Geological Survey Open-File Report 99–50–H, sion 2.0, CD–ROM. p. 45–65. Reijers, T.J.A., Petters, S.W., and Nwajide, C.S., 1997, The Udo, O.T., and Ekweozor, C.M., 1988, Comparative source rock Niger Delta Basin, in Selley, R.C., ed., African basins— evaluation of Opuama Channel Complex and adjacent produc- Sedimentary basins of the world 3: Amsterdam, Elsevier ing areas of Niger Delta: Nigerian Association of Petroleum Science, p. 151–172. Explorationists Bulletin, v. 3, no. 2, p. 10–27. U.S. Geological Survey Geologic Names Committee, 2010, Shannon, P.M., and Naylor N., 1989, Petroleum basin studies: Divisions of geologic time: U.S. Geological Survey Fact London, Graham and Trotman Limited, p. 153–169. Sheet 2010−3059, 2 p. Available at http://pubs.usgs.gov/ Short, K.C., and Stäublee, A.J., 1967, Outline of geology of fs/2010/3059/. Niger Delta: American Association of Petroleum Geologists U.S. Geological Survey World Conventional Resources Assess- Bulletin, v. 51, p. 761–779. ment Team, 2012, An estimate of undiscovered conventional oil Stacher, P., 1995, Present understanding of the Niger Delta and gas resources of the world, 2012: U.S. Geological Survey hydrocarbon habitat, in Oti, M.N., and Postma, G., eds., Fact Sheet 2012–3042, 6 p. Available at http://pubs.usgs.gov/ fs/2012/3042/. Geology of deltas: Rotterdam, A.A. Balkema, p. 257–267. U.S. Geological Survey World Energy Assessment Team, Tissot, B.P., and Welte, D.H., 1984, Petroleum formation and 2000, U.S. Geological Survey World Petroleum Assessment occurrence: Berlin, Springer-Verlag, 518 p. 2000—Description and Results: U.S. Geological Survey Tuttle, M.L., Brownfield, M.E., and Charpentier, R.R., 1999, Digital Data Series DDS–60, 4 CD–ROMs. Available at Tertiary Niger Delta (Akata-Agbada) Petroleum System http://pubs.usgs.gov/dds/dds-060/. (701901), Niger Delta Province, Nigeria, Cameroon, and Weber, K.J., and Daukoru, E.M., 1975, Petroleum geology of Equatorial Guinea, Africa, in Tuttle, M.L., Charpentier, the Niger Delta—World Petroleum Congress, 9th, v. 2, Geol- R.R., and Brownfield, M.E., eds., The Niger Delta Petro- ogy, Proceedings: London, Applied Science Publishers, Ltd., leum System; Niger Delta Province, Nigeria, Cameroon, and p. 210–221. Equatorial Guinea, Africa: U.S. Geological Survey Open-File Whiteman, A., 1982, Nigeria—Its petroleum geology, resources Report 99–50–H, p. 4–44. and potential: London, Graham and Trotman, 394 p.

M ED ATLANTIC ITE RRAN OCEAN EAN SEA

INDIAN OCEAN Niger Delta

SOUTH ATLANTIC OCEAN

INDIAN OCEAN

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