Assessment of Undiscovered Oil and Gas Resources of the Sud Province, Central- East Africa

Home , Blue Nile (state), Khartoum (state), Melut Basin, Muglad, Muglad Basin, Red Sea (state)

By Michael E. Brownfield

M ED ATLANTIC ITE RRAN OCEAN EAN SEA

Sud Province

INDIAN OCEAN

Central African Rifts Assessment Unit

SOUTH ATLANTIC OCEAN

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Chapter 14 of Geologic Assessment of Undiscovered Hydrocarbon Resources of Sub-Saharan Africa Compiled by Michael E. Brownfield

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch14_figures\ch14_figures\ch14_cover.aiDigital 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 Sud Province, central-east 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. 14, 12 p., http://dx.doi.org/10.3133/ds69GG.

ISSN 2327-638X (online) iii

Contents

Abstract...... 1 Introduction...... 1 Tectonic History and Geology of the Sud Province and Central African Rifts Assessment Unit, Central-East Africa...... 4 Source Rocks...... 4 Reservoir, Traps, and Seals...... 4 Exploration...... 10 Geologic Model...... 10 Summary...... 10 For Additional Information...... 10 Acknowledgments...... 10 References...... 12

Figures

1. Map showing the Sud Province, Central African Rifts Assessment Unit, central- east Africa...... 2 2. Map showing generalized geology of central-east Africa...... 3 3. Map showing western and central African rift system, and West African rift subsystem and central African rift subsystem...... 5 4. Geologic cross sections of the western part of the Bongor and Doseo Basins, in western Sud Province, central-east Africa...... 6 5. Generalized stratigraphic columns of the Doba, Doseo, and Salamat Basins, Central African Republic and Chad, central-east Africa...... 7 6. Generalized stratigraphic columns of the Muglad and Melut Basins, southern Sudan...... 8 7. Geologic cross sections of the Muglad and Melut Basins...... 9 8. Events chart for the eastern part of the Cretaceous-Tertiary Composite Total Petroleum System (704601) and the Central African Rifts Assessment Unit (70460101)...... 11 9. Events chart for the western part of the Cretaceous-Tertiary Composite Total Petroleum System (704601) and the Central African Rifts Assessment Unit (70460101)...... 11

Table

1. Sud Province and Central African Rifts Assessment Unit assessment results for undiscovered, technically recoverable oil, gas, and natural gas liquids...... 12 iv

Abbreviations Used in This Report

km2 square kilometers m meter mD millidarcy mg/g milligrams per gram AU assessment unit D darcy HI hydrogen index TOC total organic carbon TPS total petroleum system USGS U.S. Geological Survey Assessment of Undiscovered Oil and Gas Resources of the Sud Province, Central-East Africa

By Michael E. Brownfield

Abstract The U.S. Geological Survey estimated mean volumes of undiscovered, technically recoverable conventional oil The main objective of the U.S. Geological Survey’s and gas resources for the Central African Rifts Assessment National and Global Petroleum Assessment Project is to assess Unit in the Sud Province. The mean volumes are estimated the potential for undiscovered, technically recoverable oil at 7,310 million barrels of oil, 13,218 billion cubic feet and natural gas resources of the United States and the world. of gas, and 353 million barrels of natural gas liquids. The As part of this project, the U.S Geological Survey recently estimated mean size of the largest oil field that is expected to completed an assessment of the Sud Province, an area of be discovered is 1,112 million barrels of oil, and the estimated approximately 978,800 square kilometers that covers parts of mean size of the expected largest gas field is 3,677 billion the of Central African Republic, Chad, Ethiopia, and Sudan. cubic feet of gas. For this assessment, a minimum undiscov- This assessment was based on data from oil and gas wells, ered field size of 1 million barrels of oil equivalent was field production records, and published geologic reports. used. No attempt was made to estimate economically The Sud Province was assessed because of increased recoverable reserves. exploratory activity and interest in its future oil and gas potential. The assessment was geology based and used the total petroleum system concept. The geologic elements of a Introduction total petroleum system consist of hydrocarbon source rocks (source-rock maturation and hydrocarbon generation and The main objective of the U.S. Geological Survey’s migration), reservoir rocks (quality and distribution), and traps (USGS) National and Global Petroleum Assessment Project is (for hydrocarbon accumulation). Using these geologic criteria, to assess the potential for undiscovered, technically recover- the U.S. Geological Survey defined the Cretaceous-Tertiary able oil and natural gas resources of the United States and the Composite Total Petroleum System with one assessment world (U.S. Geological Survey World Conventional Resources unit, the Central African Rifts Assessment Unit, encompass- Assessment Team, 2012). As part of this project, the USGS ing about 848,825 square kilometers, that extends beyond the in 2012 completed an assessment of the Sud Province (fig. 1), Sud Province boundary. The assessment unit contains parts of an area of approximately 978,800 square kilometers (km2) that the Central African Republic, Chad, Ethiopia, Kenya, Sudan, covers parts of the of Central African Republic, Chad, Ethiopia, and Tanzania. and Sudan. This assessment was based on data from oil and gas Hydrocarbons were generated from Cretaceous and wells, field production records, and published geologic reports. Paleogene lacustrine rocks in the rift basins and from A geologic map of central-east Africa is shown in figure 2. Paleogene lacustrine source rocks and possibly from The Sud Province was assessed because of increased Cretaceous marine source rocks in the Kenyan Anza rift energy exploration activity and interest in its future oil and basin. Generation most likely began in the Late Cretaceous gas potential. The assessment was geology based and used the and continues to the present. Hydrocarbons migrated into total petroleum system concept. The geologic elements of a Cretaceous and Paleogene reservoirs and structural traps. total petroleum system consist of hydrocarbon source rocks Traps include tilted fault blocks, rollover folds, draped (source-rock maturation and hydrocarbon generation and anticlines, and reverse-faulted structures. Some inversion migration), reservoir rocks (quality and distribution), and traps features are recognized. Reservoir seals are Cretaceous and (for hydrocarbon accumulation). Using these geologic criteria, Paleogene shale. Rift-sag and continental analogs were used the USGS defined the Cretaceous-Tertiary Composite Total for sizes and numbers because of similar source and reservoir Petroleum System (TPS) with one assessment unit, the Central rocks and trapping mechanisms. African Rifts Assessment Unit (AU) (fig. 1), encompassing 2 Assessment of Undiscovered Oil and Gas Resources of the Sud Province, Central-East Africa

12°E 16°E 20°E 24°E 28°E 32°E 36°E 40°E 44°E

16°N NIGER Red Sea ERITREA YEMEN CHAD SUDAN

CentralShear African Zone Bongor Gulf of 12°N Basin C' Aden Doseo DJIBOUTI NIGERIA A' C Basin Muglad D' SOMALIA A B' Basin D Melut Sud ETHIOPIA Basin B 7146 8°N

CENTRAL AFRICAN SOUTH REPUBLIC SUDAN CAMEROON 4°N

SOMALIA Anza Basin UGANDA DEMOCRATIC KENYA 0° REPUBLIC OF THE GABON CONGO CONGO

RWANDA

BURUNDI ATLANTIC 4°S INDIAN OCEAN OCEAN TANZANIA

Base from U.S. Geological Survey digital data, 2002 0 120 240 360 480 KILOMETERS World Geodetic System 1984 (WGS 84) Prime Meridian, Greenwich, 0° 0 120 240 360 480 MILES Sud 7146 EXPLANATION

Sud Province boundary AFRICA Central African Rifts Assessment Unit boundary Fault—Arrows show direction of relative motion A A' Line of section INDEX MAP Figure 1. The Sud Province, Central African Rifts Assessment Unit, central-east Africa, and approximate locations of four lines of cross sections (figs. 4, 7).

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch14_figures\ch14_figures\ch14_figure01.ai Introduction 3

15°E 20°E 25°E 30°E 35°E 40°E SAUDI ARABIA ERITREA NIGER Red Sea YEMEN 15°N CHAD

Lake Chad NIGERIA SUDAN DJIBOUTI Sud ETHIOPIA Gulf of Aden 7146 10°N

SOUTH CENTRAL AFRICAN REPUBLIC SUDAN CAMEROON 5°N

EQUATORIAL DEMOCRATIC GUINEA REPUBLIC OF THE CONGO UGANDA

KENYA SOMALIA 0° GABON CONGO Lake Victoria RWANDA

ATLANTIC BURUNDI OCEAN INDIAN OCEAN TANZANIA 5°S ANGOLA

Base from U.S. Geological Survey digital data, 2002 0 150 300 KILOMETERS Geology by Persits and others, 2002 World Geodetic System 1984 (WGS 84) Prime Meridian, Greenwich, 0° 0 150 300 MILES

EXPLANATION

Quaternary Contact Sud Province boundary Tertiary Central African Rifts Assessment Unit boundary Cretaceous Inferred fault Paleozoic-Mesozoic Sud Province identifier 7146 Precambrian Gas Fields—1996 and younger Volcanic Oil Fields—1996 and younger Figure 2. Generalized geology of central-east Africa. For information about geologic units, see Persits and others (2002).

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch14_figures\ch14_figures\ch14_figure02.ai 4 Assessment of Undiscovered Oil and Gas Resources of the Sud Province, Central-East Africa about 848,825 km2, that extends beyond the USGS-defined (Mohamed and others, 2000). Each rifting event was followed Sud Province boundary (Klett and others, 1997). The by a sag event, during which thick continental clastic rocks assessment unit includes parts of the Central African Republic, were deposited (fig. 3). Chad, Ethiopia, Kenya, Sudan, and Tanzania (fig. 1). The The central African rift basins are known to contain total petroleum system was defined to include Cretaceous Cretaceous to Paleogene lacustrine and marine source rocks and Paleogene lacustrine and marine source rocks, and the that have generated hydrocarbons since the Late Cretaceous assessment unit contains Cretaceous and Paleogene clastic (Genik, 1992, 1993; Mohamed and others, 2002). Hydrocar- reservoirs, shale seals, and traps that mostly are structural and bons migrated into Cretaceous and Paleogene reservoirs and associated with extensional and transtensional faulting and structural traps. minor compressional inversion. Source Rocks

Tectonic History and Geology of the Primary source rocks are Lower and Upper Cretaceous Sud Province and Central African Rifts and Paleogene lacustrine rocks, ranging from 2,500 m to 5,000 m thick that were deposited in the rift basins (figs. 5, 6). Assessment Unit, Central-East Africa Lacustrine source rocks range from 1 to more than 5 weight percent total organic carbon (TOC) and average 2 to 3 weight The Central African Rift system was initiated during percent TOC; their hydrogen index (HI) values are greater the Early Cretaceous, at the commencement of regional than 600 milligrams per gram (mg/g) in the eastern part of northwest-southeast extension and the opening of the South the province (Schull, 1988; Mohamed and others, 2000; Dou Atlantic Ocean. The rifting continued into the Neogene and and others, 2007). Some analyzed lacustrine samples in the can be divided into two major rifting events in the western part Muglad Basin (fig. 1) had TOC values as much as 9 weight and three rifting events in the eastern part. The rift basins of percent TOC and an HI value of about 800 mg/g (Mohamed central Africa are linked along the Central African shear zone and others, 2002). right-lateral fault system (figs. 1, 3). Several thousand meters Lacustrine source rocks in the western part of the province of Lower Cretaceous clastic sediment, mostly lacustrine shale, siltstone, and sandstone were deposited during this rifting range from 1 weight percent TOC to more than 14 weight phase (Genik, 1992, 1993). percent TOC and average 2 to 3 weight percent TOC (Genik, The Cretaceous-Tertiary rift basins of the western part 1993). HI values are greater than 600 mg/g for the lacustrine of the Sud Province (fig. 1) are transtensional and are filled source rocks. with Lower Cretaceous to Neogene sedimentary rocks, The depth to the oil generation window in the Cretaceous- ranging in thickness from about 3,000 meters (m) to more Tertiary rifts in the eastern part of the Sud Province averages than 7,500 m (figs. 4, 5), that were deposited in fluvial and about 2,050 m and ranges from 1,500 m to 5,300 m (Mohamed lacustrine environments (Genik, 1992, 1993). During the and others, 2000, 2002; Dou and others, 2007). In the Chad part Early Cretaceous the first rifting event allowed deposition of of the Sud Province the depth of the oil window ranges from fluvial and lacustrine rocks in rift basins of southern Chad and 2,300 m to 5,000 m (Genik, 1993). the Central African Republic (fig. 2). In the Late Cretaceous (Cenomanian to Turonian), a regional rifting event deposited thick continental clastic rocks in the eastern part of the Reservoirs, Traps, and Seals province. During the Late Cretaceous and Paleogene, transten- The Cretaceous and Paleogene sandstone reservoirs sional faulting and sag events in the western part of the Sud in the western part of the Central African Rifts AU are Province led to deposition of fluvial and lacustrine rocks. The extensional and transtensional rift basins in the generally poorly defined in terms of their distribution and eastern part of the Province are filled with Jurassic? to their net thickness. The reservoir quality is fair to good; Neogene sedimentary rocks (figs. 6, 7) that range in thickness porosities range from 12 to 32 percent and permeabilities from 6,000 m to more than 13,000 m; these rocks were from 10 millidarcies (mD) to 10 darcies (D) (Genik, 1993). deposited in fluvial and lacustrine environments (Mohamed These rocks were generally deposited in fluvial environ- and others, 2000, 2002; Dou and others, 2007). The initial ments although some reservoirs contain lacustrine-delta rifting event began in the latest Jurassic and continued through sandstone. Reservoir characteristics are good to excellent in the Early Cretaceous (fig. 3), resulting in the deposition of the Cretaceous fluvial sandstone reservoirs in the eastern part Lower Cretaceous lacustrine source rocks (figs. 3, 4). The of the assessment unit and have excellent reservoir quality; second rifting event began in the Turonian and continued porosities range from 8 to 25 percent and permeabilities are into the Senonian, and the third rifting event occurred during as much as 1,600 mD (Mohamed and others, 2000; Dou and the Paleogene, at the same time that Red Sea rifting began others, 2007). Tectonic History and Geology of the Sud Province and Central African Rifts Assessment Unit, Central-East Africa 5

0° 4°E 8°E 12°E 16°E 20°E 24°E 28°E 32°E 36°E 40°E 44°E

24°N LIBYA EGYPT ALGERIA SAUDI ARABIA Kafra Grein MALI 20°N Tenere Red Sea

Gao Tefidet NIGER Atbara 16°N SUDAN ERITREA CHAD YEMEN N’ Dgel Edgi White Nile Khartoum Blue Nile

BURKINA Bornu Bagarra DJIBOUTI 12°N FASO Kosti

BENIN NIGERIA Bongor Bida Muglad Yola Salamat ETHIOPIA GHANA Doba Doseo SOMALIA 8°N Benoue Melut CENTRAL SOUTH Pibor TOGO AFRICAN SUDAN REPUBLIC Jonglei Loelli CAMEROON Mongala 4°N EQUATORIA GUINEA SOMALIA SAO TOME Anza AND PRINCIPE UGANDA 0° CONGO GABON KENYA DEMOCRATIC RWANDA ATLANTIC REPUBIC OF OCEAN THE CONGO INDIAN 4°S BURUNDI TANZANIA OCEAN ANGOLA

Base from U.S. Geological Survey digital data, 2002 0 150 300 450 600 KILOMETERS World Geodetic System 1984 (WGS 84) Prime Meridian, Greenwich, 0° 0 150 300 450 600 MILES

EXPLANATION

West and Central African Rift General trace of East African Rift System System Central African Subsystem WCARS boundary—Dashed where uncertain West African Subsystem Loelli Basin identifier Fault—Dashed where uncertain Figure 3. Western and Central African rift system. West African rift subsystem and Central African rift subsystem. Modified from Genik (1993).

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SOUTH NORTH

A A' Bongor Basin METERS HM 0 Ku

2,500 Kl

5,000

7,500

0 2 4 6 KILOMETERS

0 2 4 6 MILES SOUTHEAST SOUTHWEST

B B' METERS Doseo Basin 0 HM

2,500 Ku

5,000 Kl 7,500

0 2 4 6 KILOMETERS

0 2 4 6 MILES

EXPLANATION HM Holocene to Miocene

Ku Upper Cretaceous

Kl Lower Cretaceous

Precambrian Contact—Dashed where uncertain Fault Major seismic reflector Oil and gas discovery well

Figure 4. Schematic geologic cross sections of the western part of the Bongor and Doseo Basins, showing sedimentary fill in the western part of the Sud Province, central-east Africa. Lines of cross section A–A‘ and B–B‘ on figure 1. Modified from Genik (1992).

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch14_figures\ch14_figures\ch14_figure04.ai Tectonic History and Geology of the Sud Province and Central African Rifts Assessment Unit, Central-East Africa 7

Depth Lithology in Age kilometers Doba Doseo Salamat 0 H H Holocene- M M Miocene

P Neogene P 1 Oligocene UK Tertiary Eocene

UK Paleogene Paleocene 2

Maastrichtian

LK Senonian

LK Upper Cretaceous

Albian Cretaceous

5 Less than 8,000 meters

LK? Aptian- Barremian- Neocomian Lower Cretaceous 6 Less than 7,000 meters LK?

Less than Mesozoic-Paleozoic 7 7,000 meters Precambrian

EXPLANATION Marine Shale Volcanic Tested oil Extent uncertain Nonmarine Basement Shale-Claystone— Source rocks Contact unknown Unconformity Sandstone Tested oil and gas

Figure 5. Generalized stratigraphic columns of the Doba, Doseo, and Salamat Basins, Central African Republic and Chad (see fig. 3), central-east Africa. Modified from Genik (1992, 1993). H, Holocene; M, Miocene; Pe, Paleogene; UK, Upper Cretaceous; LK, Lower Cretaceous.

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Muglad Basin Melut Basin Geologic time scale; Tectonic Formation Lithology Geologic time Formation Lithology Tectonic thickness of unit in meters event scale event

Holocene-Miocene Zeraf Quat Pleistocene Agor 760 Sag Daga Adok

Miocene Miadol Sag Neogene Jimidi

Oligocene- Oligocene Lau upper Eocene Tendi Tertiary

4,115 Kordofan Group Rifting event 3 Eocene Adar

Nayil Yabus Paleogene Paleocene Rifting event 3 Paleocene Amal Sag Samma 760 Baraka Lower Senonian- Ghazal Turonian Rifting event 2 Melut 1,830 Zarga

Darfir Group Aradeiba Upper Cenomanian- upper Albian Bentiu Sag 1,525 Rifting event 2 Galhak Cretaceous

Albian-Aptian Abu Cretaceous 1,830 gabra Rifting event 1 Barremian- Sharaf Neocomian Lower Al Gayger 760

Tithonian- Rifting event 1 older 90 Jurassic? Precambrian

EXPLANATION

Sandstone and Lacustrine source siltstone rock Shale-Claystone— Precambrian basement Minor Type I and Type III source Unconformity rocks Figure 6. Generalized stratigraphic columns of the Muglad and Melut Basins, southern Sudan (see fig. 3). Modified from Mohamed and others (2000) and Dou and others (2007). Quat, Quaternary.

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch14_figures\ch14_figures\ch14_figure06.ai Tectonic History and Geology of the Sud Province and Central African Rifts Assessment Unit, Central-East Africa 9

SOUTHWEST Muglad Basin NORTHEAST Rakuba Sub basin Sharaf-Abu Gabra Ridge Nugara Sub basin C Abanus-1 Hashab-1 C' METERS 0 HM HM T 1,000 TK T 2,000 TK

3,000 Ku Ku 4,000 Kl 5,000 Kl

6,000

7,000 8,000

9,000

10,000

0 2 4 6 8 10 KILOMETERS

0 2 4 6 8 10 MILES

D D' METERS Melut Basin 0 HM M 3,000 EPa

6,000 Ku Kl 9,000

12,000

0 2 4 6 8 KILOMETERS

0 2 4 6 8 MILES EXPLANATION

Contact HM Holocene to Miocene Pa Paleocene Fault—Arrows shows T Tertiary Ku Upper Cretaceous relative motion Hashab-1 Tk Tertiary to Upper Cretaceous Kl Lower Cretaceous Well and identifier

M Miocene Precambrian EPa Eocene to Paleocene Figure 7. Schematic geologic cross sections of the Muglad and Melut Basins showing sedimentary fill in southern Sudan. Lines of cross section C–C‘ and D–D‘ shown on figure 1. Modified from Mohamed and others (2002) and Dou and others (2007).

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Paleogene sandstone reservoirs were deposited in a • Seals consist of Cretaceous and Paleogene shale. fluvial environment. The sandstones are generally thin, but stacked reservoirs may be as much as several hundred meters • Rift-sag and continental analogs (Charpentier and thick. Porosities range from 22.1 to 40.8 percent and average others, 2007) were used for assessment sizes and num- 29 percent (Dou and others, 2007). The Paleogene sandstone bers because of similar source and reservoir rocks and reservoirs are interbedded with shale and the reservoir trapping mechanisms. characteristics are good to excellent. Reservoir seals are Upper Cretaceous and Paleogene Events charts (figs. 8, 9) for the eastern and western shales. The limited lateral extents of fluvial shale seals have parts of the Sud Province and the Central African Rifts AU been considered a problem in some areas of the assessment summarize the age of the source, seal, and reservoir rocks and unit Genik, 1993). the timing of trap development and generation and migration Traps are generally structural and include anticlines, tilted- of hydrocarbons. fault blocks, rollover folds, drape anticlines, and reverse-faulted structures (Schull, 1988). Some inversion features, such as flower structures, have been recognized (Warren, 2009). Summary

Using a geology-based assessment, the U.S. Geological Exploration Survey estimated mean volumes of undiscovered, technically recoverable conventional oil and gas resources for the At the time of this 2010 assessment, the province Cretaceous-Tertiary Rifts Assessment Unit in the Sud Province contained 113 oil fields—18 in Chad and 95 in Sudan—and (table 1). The mean volumes are estimated at 7,310 million is considered to be underexplored on the basis of its explora- barrels of oil, 13,218 billion cubic feet of gas, and 353 million tion activity. The province contains two gas fields, and several barrels of natural gas liquids. The estimated mean size discoveries reported associated gas in oil fields (IHS, 2009). of the largest oil field that is expected to be discovered is The producing oil fields and recent petroleum discoveries are 1,112 million barrels of oil, and the estimated mean size of limited to Cretaceous-Tertiary rift basins. the expected largest gas field is 3,677 billion cubic feet of gas. For this assessment, a minimum undiscovered field size of 1 million barrels of oil equivalent was used. No attempt was Geologic Model made to estimate economically recoverable reserves.

The geologic model developed for the assessment of conventional oil and gas in the Sud Province and the Central African Rifts AU of central Africa is as follows: For Additional Information • Rift basins in the Central African Rifts AU are known Assessment results are available at the USGS Central to contain hydrocarbons. Hydrocarbons were generated Energy Resources Science Center website: http://energy.cr.usgs. from Cretaceous and Paleogene lacustrine rocks in gov/oilgas/noga/ or contact Michael E. Brownfield, the assessing the rift basins in Chad and Sudan. Hydrocarbons were geologist ([email protected]). generated from Paleogene lacustrine source rocks and possibly from Cretaceous marine source rocks in the Kenyan Anza rift basin. Generation most likely began Acknowledgments in the Late Cretaceous and continues to the present. The author wishes to thank Mary-Margaret Coates, • Hydrocarbons migrated into Cretaceous and Paleogene Jennifer Eoff, Christopher Schenk, and David Scott for their reservoirs and structural traps. suggestions, comments, and editorial reviews, which greatly • Hydrocarbon traps are generally structural, such as improved the manuscript. The author thanks Wayne Husband tilted-faulted blocks, rollover folds, draped anticlines, for his numerous hours drafting many of the figures used and reverse-faulted structures. Some inversion features in this manuscript, and Chris Anderson, who supplied the are recognized. geographic information system files for this assessment. Geologic Model 11

PETROLEUM PETROLEUM

SYSTEM EVENTS SYSTEM EVENTS

ACCUMULATION

MIGRATION- MIGRATION- ROCK UNITS RESERVOIR ROCKS

OVERBURDEN ROCKS

ROCK UNITS RESERVOIR ROCKS

PRESERVATION OVERBURDEN ROCKS

SOURCE ROCKS SEAL ROCKS TRAP FORMATION PRESERVATION

Age in million years (Ma) SOURCE ROCKS SEAL ROCKS TRAP FORMATION

GENERATION- Age in million years (Ma) GENERATION- 0 0 Plio Plio Neogene Neogene Mio Mio 23 23 Olig Olig

Paleogene Eoc Paleogene Eoc 50 50 Pal Pal 65 65

L L

Cretaceous Cretaceous 100 100

E E

146 146 150 L 150 L

M M Jurassic Jurassic

E E 200 200 200 200

L L Triassic Triassic

M M E E 250 250 251 L 251 L Permian Permian E E

Figure 8. Events chart for the eastern part of the Cretaceous- Figure 9. Events chart for the western part of the Cretaceous- Tertiary Composite Total Petroleum System (704601) and the Tertiary Composite Total Petroleum System (704601) and the Central African Rifts Assessment Unit (70460101). Gray, rock Central African Rifts Assessment Unit (70460101). Gray, rock units present; yellow, age range of reservoir rock; green, age units present; yellow, age range of reservoir rock; green, age ranges of source, seal, and overburden rocks and the timing of ranges of source, seal, and overburden rocks and the timing of trap formation and generation, migration, and preservation of trap formation and generation, migration, and preservation of hydrocarbons; wavy line, unconformity. Divisions of geologic time hydrocarbons; wavy line, unconformity. Divisions of geologic time conform to dates in U.S. Geological Survey Fact Sheet 2010–3059 conform to dates in U.S. Geological Survey Fact Sheet 2010–3059 (U.S. Geological Survey Geologic Names Committee, 2010). Ma, (U.S. Geological Survey Geologic Names Committee, 2010). Ma, million years ago; Plio, Pliocene; Mio, Miocene; Olig, Oligocene; million years ago; Plio, Pliocene; Mio, Miocene; Olig, Oligocene;

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch14_figures\ch14_figures\ch14_figure08.aiEoc, Eocene; Pal, Paleocene, L, Late;\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch14_figures\ch14_figures\ch14_figure09.ai E, Early; M, Middle. Eoc, Eocene; Pal, Paleocene, L, Late; E, Early; M, Middle. 12 Assessment of Undiscovered Oil and Gas Resources of the Sud Province, Central-East Africa

Table 1. Sud Province and Central African Rifts Assessment unit assessment 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 the 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. Gray shading indicates not applicable] Largest Total undiscovered resources Total Petroleum Systems (TPS) Field expected Oil (MMBO) Gas (BCFG) NGL (MMBNGL) and Assessment Units (AU) type mean F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean field size Sud Province-Cretaceous-Cenozoic Composite TPS Oil 1,112 3,141 6,809 13,222 7,310 531 1,321 3,169 1,522 14 35 87 41 Central African Rifts AU Gas 3,677 2,824 9,822 26,776 11,696 73 259 732 312 Total Conventional Resources 3,141 6,809 13,222 7,310 3,355 11,143 29,915 13,218 87 294 891 353

References Mohamed, A.Y., Pearson, M.J., Ashcroft, W.A., and Whiteman, A.J., 2002, Petroleum maturation modeling, Abu Gabra– Charpentier, R.R., Klett, T.R., and Attanasi, E.D., 2007, Sharaf area, Muglad Basin, Sudan: Journal of African Earth Database for assessment unit-scale analogs (exclusive of the Sciences v. 35, no. 2, p. 331–344. United States) Version 1.0: U.S. Geological Survey Open- Persits, F.M., Ahlbrandt, T.S., Tuttle, M.L., Charpentier, R.R., File Report 2007–1404, 36 p., CD–ROM. Brownfield, M.E., and Takahashi, K.I., 2002, Map show- Dou, L., Xiao, K., Cheng, D., Shi, B., and Li, Z., 2007, Petroleum ing geology, oil and gas fields, and geologic provinces of geology of the Melut Basin and the Great Palogue field, Sudan: Africa: U.S. Geological Survey Open-File Report 97–470A, Marine and Petroleum Geology, v. 24, no. 3, p. 129–144. Version 2.0, CD–ROM. Genik, G.J., 1992, Regional framework, structural and petroleum Schull, T.J., 1988, Rift basins of interior Sudan—Petroleum aspects of rift basins in Niger, Chad and the Central African exploration and discovery: American Association of Petro- leum Geologists Bulletin, v. 72, no. 10, p. 1128–1142. Republic (C.A.R.): Tectonophysics, v. 213, no. 1, p. 169–185. U.S. Geological Survey Geologic Names Committee, 2010, Genik, G.J., 1993, Petroleum geology of the Cretaceous- Divisions of geologic time: U.S. Geological Survey Fact Tertiary rifts basins in Niger, Chad, and Central African Sheet 2010−3059, 2 p. Available at http://pubs.usgs.gov/ Republic: American Association of Petroleum Geologists fs/2010/3059/. Bulletin, v. 73, no. 8, p. 153–168. U.S. Geological Survey World Conventional Resources IHS Energy, 2009, International petroleum exploration and Assessment Team, 2012, An estimate of undiscovered production database [current through December 2009]: conventional oil and gas resources of the world, 2012: available from IHS Energy, 15 Inverness Way East, Engle- U.S. Geological Survey Fact Sheet 2012–3042, 6 p. wood, Colo. 80112 USA. Available at http://pubs.usgs.gov/fs/2012/3042/. Klett, T.R., Ahlbrandt, T.A., Schmoker, J.W., and Dolton, Warren, M.J., 2009, Tectonic inversion and petroleum system G.L., 1997, Ranking of the world’s oil and gas provinces by implications in the rifts of central Africa: Frontiers + Inno- known petroleum volumes: U.S. Geological Survey Open- vation, 2009 Canadian Society of Petroleum Geology, Cana- File Report 97–463, CD–ROM. dian Society of Exploration Geophysicists, and Canadian Mohamed, A.Y., Iliffe, J.E., Ashcroft, W.A., and Whiteman, Well Logging Society Convention, Calgary, May 4–6, 2009, A.J., 2000, Burial and maturation history of the Heglig field Proceedings, p. 461–464. Available at http://www.cspg.org/ area, Muglad Basin, Sudan: Journal of Petroleum Geology, documents/Conventions/Archives/Annual/2009/266.pdf. v. 23, no. 1, p. 107–128. Last accessed March 5, 2012.

M ED ATLANTIC ITE RRAN OCEAN EAN SEA

Sud Province

INDIAN OCEAN

Central African Rifts Assessment Unit

SOUTH ATLANTIC OCEAN

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