Assessment of Undiscovered Oil and Gas Resources of the Coastal Province, East Africa

By Michael E. Brownfield

M ED ATLANTIC ITE RRAN OCEAN EAN SEA

INDIAN OCEAN

Tanzania Coastal

SOUTH

INDIAN OCEAN

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Chapter 12 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_ch12_figures\ch12_figures\ch12_cover.ai 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 Tanzania Coastal Province, 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. 12, 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 Tanzania Coastal Province, East Africa...... 4 Petroleum Occurrence in the Tanzania Coastal Province, East Africa...... 4 Source Rocks...... 4 Reservoirs, Traps, and Seals...... 4 Exploration...... 9 Geologic Model...... 9 Resource Summary...... 11 For Additional Information...... 11 Acknowledgments...... 11 References...... 12

Figures

1. Map showing locations of the Tanzania Coastal Province and Mesozoic- Cenozoic Reservoirs Assessment Unit along the central coast of East Africa...... 2 2. Map showing generalized geology of East Africa...... 3 3. Map showing reconstruction of the early breakup of Gondwana during the Early Jurassic...... 5 4. Stratigraphic columns of coastal Mozambique, the , and coastal Tanzania, Morondava Basin, and Seychelles...... 6 5. Composite stratigraphic column of Tanzania coastal basins...... 7 6. Cross section of the Rovuma Delta, southern Tanzania...... 8 7. Seismic cross section A–A‘ of the Ruvu and deep-marine basins and the Channel, Tanzania...... 9 8. Seismic cross sections B–B‘, Ruvu and coastal basins and the Dar es Salaam platform, Tanzania, and C–C‘, Selous, Mandawa, and deep-marine basins, Tanzania...... 10 9. Events chart for the Mesozoic-Cenozoic Composite Total Petroleum System (727301) and the Mesozoic-Cenozoic Reservoirs Assessment Unit (72730101)...... 11

Table

1. Tanzania Coastal Province assessment results for undiscovered, technically recoverable oil, gas, and natural gas liquids...... 12 iv

Abbreviations Used in This Report

km2 square kilometers mg HC/g TOC milligrams hydrocarbon per gram total organic carbon AU assessment unit 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 Tanzania Coastal Province, East Africa

By Michael E. Brownfield

Abstract Most generated hydrocarbons migrated into Cretaceous and Paleogene reservoirs and traps. Hydrocarbon traps are mostly The main objective of the U.S. Geological Survey’s structural in the syn-rift rock units and both structural and National and Global Petroleum Assessment Project is to assess stratigraphic in the post-rift rock units. The primary reservoir the potential for undiscovered, technically recoverable oil and seals are Mesozoic and Cenozoic mudstone and shale. Rifted natural gas resources of the United States and the world. As passive margin analog was used for assessment sizes and part of this program, the U.S. Geological Survey completed numbers because of similar source, reservoirs, and traps. an assessment of the Tanzania Coastal Province, an area of Using a geology-based assessment, the U.S. Geological approximately 250,373 square kilometers that covers parts of Survey estimated mean volumes of undiscovered, technically Kenya and Tanzania. The Tanzania Coastal Province contains recoverable conventional oil and gas resources for the rift, marginal-sag, and passive-margin rocks of Middle Mesozoic-Cenozoic Reservoirs Assessment Unit in the Jurassic to Holocene age. This assessment was based on data Tanzania Coastal Province. The mean volumes are estimated from oil and gas exploration wells, producing fields, and at 2,806 million barrels of oil, 71,107 billion cubic feet of published geologic reports. gas, and 2,212 million barrels of natural gas liquids. The estimated mean size of the largest oil field that is expected to The Tanzania Coastal Province and associated assessment be discovered is 594 million barrels of oil, and the estimated unit was assessed because of increased exploratory activity, mean size of the expected largest gas field is 6,162 billion recent discoveries, and increased interest in its future oil and cubic feet of gas. For this assessment, a minimum undiscov- gas potential. The assessment was geology based and used the ered field size of 5 million barrels of oil equivalent was total petroleum system concept. The geologic elements of a used. No attempt was made to estimate economically total petroleum system consist of hydrocarbon source rocks recoverable reserves. (source rock maturation and hydrocarbon generation and migration), reservoir rocks (quality and distribution), and traps for hydrocarbon accumulation. Using these geologic criteria, the U.S. Geological Survey defined the Mesozoic-Cenozoic Introduction Composite Total Petroleum System with one assessment unit, the Mesozoic-Cenozoic Reservoirs Assessment Unit, an area The main objective of the U.S. Geological Survey’s of approximately 169,965 square kilometers. At the time of (USGS) National and Global Petroleum Assessment Project is the 2012 assessment, the Tanzania Coastal Province contained to assess the potential for undiscovered, technically recover- eight gas accumulations exceeding the minimum size of able oil and natural gas resources of the United States and the 5 million barrels of oil equivalent. This province is considered world (U.S. Geological Survey World Conventional Resources to be underexplored on the basis of its exploration effort. Assessment Team, 2012). As part of this program, the USGS Oil and gas were generated from Permian to Jurassic recently completed an assessment of the Tanzania Coastal Karoo-age lacustrine and continental source rocks (rift stage) Province (fig. 1), an area of approximately 250,373 square averaging 4.0 to 5.0 weight percent total organic carbon, from kilometers (km2) that covers parts of Kenya and Tanzania. Early to Middle Jurassic restricted-marine rocks contain- The Tanzania Coastal Province contains rift, marginal-sag, ing as much as 9 weight percent total organic carbon, and and passive-margin rocks of Middle Jurassic to Holocene age. from Cretaceous Type II source rocks containing as much as This assessment was based on data from oil and gas explora- 12 weight percent organic carbon. Hydrocarbon generation tion wells, producing fields (IHS Energy, 2009), and published most likely began in the latest Jurassic–earliest Cretaceous and geologic reports. A geologic map of Tanzania is shown in continues today in the offshore parts of the assessment unit. figure 2. 2 Assessment of Undiscovered Oil and Gas Resources of the Tanzania Coastal Province, East Africa

30°E 34°E 38°E 42°E 46°E 50°E 54°E 58°E 62°E 66°E 70°E

KENYA 2°S RWANDA

BURUNDI SEYCHELLES Tanzania Coastal 6°S TANZANIA 7273

10°S ZAMBIA COMOROS

Mayotte 14°S MALAWI INDIAN OCEAN

18°S MOZAMBIQUE MADAGASCAR ZIMBABWE MAURITIUS

Réunion 22°S

SWAZILAND 26°S SOUTH AFRICA

30°S LESOTHO

34°S

Base from U.S. Geological Survey digital data, 2002 0 150 300 KILOMETERS World Geodetic System 1984 (WGS 84) Prime Meridian, Greenwich, 0° 0 150 300 MILES EXPLANATION AFRICA Tanzania Coastal Province boundary Mesozoic-Cenozoic Reservoirs Assessment Tanzania Unit boundary Coastal 7273 Gas field

INDEX MAP Figure 1. Locations of the Tanzania Coastal Province and Mesozoic-Cenozoic Reservoirs Assessment Unit along the central coast of East Africa.

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch12_figures\ch12_figures\ch12_figure01.ai Introduction 3

Ogaden Aswa Shear Zone Basin MOGADISHU

Continent-oceanic boundary (COB) Congo Basin

Cupa Fault Zone Mombasa Somali Oceanic Basin TANZANIA

Dar es Salaam Mandawa Basin Rovuma Delta

Majunga INDIAN OCEAN Basin MOZAMBIQUE

Tsimiroro Field Davie Fracture Zone Beira

1,000

Mozambique Channel Mozambique MADAGASCAR Basin

Kalahari Basin MAPUTO Continent-oceanic boundary Morondava (COB) Basin Karroo Basin 0 200 400 600 KILOMETERS

0 200 400 600 MILES EXPLANATION

Tertiary—Volcanic province Continental crust—Palo fill Post Early Jurassic—Passive Contact margin basin Fault or fault zone—Dashed where approximate. Arrows show relative Permian-Triassic–Early motion Jurassic—Karoo-age rock Graben—Teeth on downthrown side Phanerozoic—Intracratonic Bathymetric contour, 1,000 meter basin line—Location approximate Undifferentiated—Precambrian basement Figure 2. Generalized geology of East Africa. Modified after Ophir Energy Company (2011). 4 Assessment of Undiscovered Oil and Gas Resources of the Tanzania Coastal Province, East Africa The Tanzania Coastal Province and associated assessment Petroleum Occurrence in the Tanzania unit were assessed because of increased energy exploration activity, recent discoveries, and increased interest in its future Coastal Province, East Africa oil and gas potential. The assessment was geology based and used the total petroleum system concept. The geologic Source Rocks elements of a total petroleum system consist of hydrocar- bon source rocks (source-rock maturation and hydrocarbon The Mesozoic-Cenozoic Composite TPS was defined to generation and migration), reservoir rocks (quality and include Paleozoic to Paleogene source rocks and conventional distribution), and traps for hydrocarbon accumulation. Using reservoirs (figs. 4, 5). The Permian to Triassic section contains these geologic criteria, the USGS defined the Mesozoic- fluvial and lacustrine source rock in which Type I and Type III Cenozoic Composite Total Petroleum System (TPS) with kerogen contain 1.0 to 6.7 weight percent total organic carbon one assessment unit, the Mesozoic-Cenozoic Reservoirs (TOC); some samples have as much as 17.4 weight percent. Assessment Unit (AU) (fig. 1), an area of approximately Kagya (1996) reported that Triassic and Lower Jurassic source 169,965 km2. rocks contained TOC values ranging from 1.23 to 7.16 weight percent, and Nagati (2011) reported Jurassic source rock with TOC contents as much as 8.4 weight percent. The Early to Middle Jurassic section contains restricted marine Type II Tectonic History and Geology kerogen source rock and marginal marine, deltaic Types II and of the Tanzania Coastal Province, III kerogen source rocks, and Type I lacustrine source rock (Cope, 2000; Kejato, 2003; Rusk, Bertagne & Associates, 2003). East Africa The Early to Middle Jurassic lacustrine Type I and restricted marine Type II source rocks contain as much as 8.7 weight The Tanzania Coastal Province is directly related to percent TOC (Cope, 2000). Type II and III kerogen source rocks the breakup of Gondwana (fig. 3) in the late Paleozoic and of Cretaceous and Paleogene age have been identified in the Mesozoic (Reeves and others, 2002). The province developed Tanzania Coastal Province (Cope, 2000). The Cretaceous marine in four phases: (1) pre-rift stage that started during the sources contain TOC contents as much as 7.4 weigh percent Carboniferous, during which a mantle plume caused uplift, and hydrogen index (HI) values as much as 396 milligrams extension, microplate formation, rifting, and volcanism; hydrocarbon per gram total organic carbon (mg HC/g TOC) and (2) a syn-rift phase that started during the Permo-Triassic and the Paleogene marine sources contain 12.1 weight percent and continued into the Jurassic, forming grabens and half-grabens HI values as much as 688 mg HC/g TOC (Cope, 2000). and depositing possible lacustrine and continental source Generation of syn-rift Karoo age source rocks most likely rocks; (3) a syn-rift-drift phase that began in the Middle began in the Middle Jurassic, whereas Middle Jurassic to Early Jurassic and continued into the Paleogene, during which Cretaceous syn-rift source rocks began in the Late Jurassic marine clastic and carbonate rocks were deposited, and marine to Early Cretaceous (Cope, 2000). Generation of hydrocar- source rocks were deposited during periods of restricted- bons by early post-rift sources most likely began in the Late marine conditions; and (4) a passive-margin phase that Cretaceous, whereas the drift and post-rift source rocks most began in the late Paleogene and continues to the present. The likely began generating hydrocarbons in the Late Cretaceous. stratigraphic section present in the Tanzania Coastal Province Hydrocarbon generation most likely continues today in the is generally the same as the section present in the coastal offshore parts of the assessment unit (Cope, 2000). Morandava Basin and coastal Mozambique (figs. 2, 4; Rusk, Bertagne & Associates, 2003; Fugro Multi Client Services, Reservoirs, Traps, and Seals 2010). The opening of the Indian Ocean began in the Permian The Tanzania Coastal Province contains Mesozoic and and continued into the Jurassic during the syn-rift phase. In Cenozoic clastic reservoirs. Triassic to Middle Jurassic syn-rift the Middle Jurassic, Madagascar, India, and the Seychelles rocks contain possible alluvial fans, fan deltas, fluvial deltas, separated from Africa and formed a passive margin and a and lacustrine sandstones reservoirs (Cope, 2000). The Late carbonate platform that was later covered by Upper Jurassic Jurassic post-rift rocks contain reef and platform carbonate to Cretaceous marine clastic deposits (figs. 4, 5). During the rocks that are potential reservoirs. The post-rift Cretaceous middle Cretaceous, the rift-sag passive-margin basin again rocks contain regressive and transgressive marine sandstone, became the site of deposition of marine sediments. Deltaic slope-turbidite channel and sandstone and basin-floor fan progradation of the Rovuma (fig. 6) and Rufiji Deltas began in sandstone reservoirs (Cope, 2000; Ophir Energy Company, the Oligocene and continues today. These deltas are the sites 2007, 2011). Upper Cretaceous and Cenozoic passive-margin of several recent large gas discoveries. rocks contain possible carbonate reservoirs and Maastrichtian Petroleum Occurrence in the Tanzania Coastal Province, East Africa 5

HORN OF AFRICA

Anza Rift KENYA

Saurastra Cambay Rift

INDIA

TANZANIA SEYCHELLES Narmada-Son MADAGASCAR

INDIA Mikume Rift

Selous Basin

SRI LANKA NORTH

MOZAMBIQUE

EAST ANTARCTICA

0 100 200 KILOMETERS

0 100 200 MILES

EXPLANATION

Precambrian crustal fragment

Rift-related rock Line of latitude or longitude— Oriented as on modern map Figure 3. Reconstruction of the early breakup of Gondwana during the Early Jurassic (200 Ma). Modified from Reeves and others (2002). 6 Assessment of Undiscovered Oil and Gas Resources of the Tanzania Coastal Province, East Africa

Age Coastal Mozambique Channel Coastal Tectonic Tectonic Mozambique and Coastal Tanzania Morandava Basin events Seychelles events W Lithology E Envir. Lithology W Lithology E Envir. East Africa W Lithology E Envir. Seychelles Fluvial Deltaic to Deltaic cont.

Neogene Deltaic Shallow Marine marine R Drift TERTIARY R Paleogene breakup Rift Seychelles-India Marine

R Upper Marginal sag and passive margin Shallow marine and open

and marginal marine R Marginal sag and drift CRETACEOUS Restricted marine, open to continental Lower Shallow marine Marine Upper and drift Madagascar- Madagascar-

R Seychelles-India ? Seychelles-India Rift, marginal sag breakup from Africa breakup from Africa M Rift and marginal sag marine, and open marine Restricted marine, shallow JURASSIC Zones of reservoir potential ? R Lower lagoonal to continental Rifting and marginal sag Shallow marine Upper TRIASSIC M ? R

L ? ? and uplift

U ? Continental with minor marginal marine Recurrent rifting and uplift

? ? Recurrent rifting L

PERMIAN R marginal marine Continental with minor marginal marine Continental with minor Upper

Middle- ? IFEROUS CARBON-

BRIAN Basement PRECAM-

EXPLANATION

Sandstone Limestone Reservoir rock, East Africa R Potential reservoir Oil field Sandstone and conglomerate Salt Contact—Dashed where location approximate Gas field Shale Igneous rock—Extrusive Unconformity Sandy shale Igneous rock—Oceanic crust Extent uncertain Source rock Calcareous shaley marlstone Basement

Figure 4. Generalized stratigraphic columns for Coastal Mozambique, Mozambique Channel and Coastal Tanzania, Coastal Morondava Basin, and Seychelles along the east coast of Africa (see fig. 1). Carb., Carboniferous; cont., continental; Envir., environment; L, Lower; M, Middle; U, Upper; W, west; E, east. Modified from Rusk, Bertagne & Associates (2003) and Fugro Multi Client Services (2010).

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch12_figures\ch12_figures\ch12_figure04.ai Petroleum Occurrence in the Tanzania Coastal Province, East Africa 7

Composite Stratigraphic Column for EXPLANATION Tanzanian Coastal Basins Sandstone Quaternary Shale Pliocene upper Carbonate rock middle Salt

Miocene deltaic sands in lower Miocene Zanzibar channel with lignites Precambrian basement and carbonaceous shale Oligocene Contact (gas shows) Unconformity upper Tertiary Carbonaceous shale middle and lignite

Gas shows in Songosongo area, lower Eocene Zanzibar & Maflia wells Paleocene Maastrichtian Sands in Zanzibar and Maflia wells Campanian Marine shale Santonian

Coniacian Senonian Upper Aptian Kihuluhulu Upper marlstone and lower Albian Turonian Kigongo marlstone Cenomanian Albian deltaic sand acting as reservoirs in Songosongo gas Albian fields and Maflia channel? Aptian Cretaceous Barremian Continental Makonde beds Hauterivian Lower Regressive Neocomian sand Valanginian

Berriasian Neocomian

Marine shales Tithonian Kimmeridgian Oxfordian Upper Shallow marine limestones Callovian reefal, oolitic & detrital Bathonian probably present over the whole coast Bajocian Middle Aalenian Jurassic Evaporite sequence in Toarcian Mandawa salt basin Pleinsbachian Lagoonal marine shales excellent Sinemurian Lower source potential in Mandawa-7 Hettangian Permo-Triassic Continental sandstones with carbonaceous shale and lignite Precambrian

Figure 5. Composite stratigraphic column of Tanzania coastal basins. Modified from Mbede and Dualeh (1997).

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch12_figures\ch12_figures\ch12_figure05.ai 8 Assessment of Undiscovered Oil and Gas Resources of the Tanzania Coastal Province, East Africa

Neocomian Songo Songo and Miocene and Oligocene Nyuni Fields Msimbati and Mnazi Bay Fields

Paleocene INDIAN OCEAN Cenomanian Seafloor

Jurassic salt?

Santonian Campanian

NOT TO SCALE EXPLANATION

Neogene Jurassic Gas discovies and prospects Paleogene Salt Oil prospects Maastrichtian-Campanian Basement—Triassic Contact Santonian-Cenomanian Reservoir and potential Unconformity reservoir Fault Lower Cretaceous

Figure 6. Schematic cross section of the Rovuma Delta, southern Tanzania. Modified from Ophir Energy Company PLC (2011). Not to scale.

and Paleocene turbidite reservoirs (slope channels, salt structures, drape anticlines, and flower structures (Ophir sandstones, and basin-floor fans). Volcanic rocks found within Energy Company, 2007, 2011). Upper Cretaceous and the Karoo-age and Cretaceous section may have degraded Paleogene post-rift rocks (drift and passive margin) contain some of the reservoirs by thermal alteration of minerals in the both structural and stratigraphic traps in growth-fault-related reservoir rock units. structures, rotated fault blocks within the continental shelf, The Mesozoic-Cenozoic Reservoirs AU (fig. 1) contains deep-water fans, turbidite channels and sandstones, and slope reservoirs that mostly are associated with growth-fault-related truncations along the present day shelf and paleoshelf edge structures, rotated fault blocks within the continental shelf, (Cope, 2000; Ophir Energy Company, 2007). For example, the deep-water fans, turbidite units, and slope truncations along Rovuma River delta (fig. 6) contains turbidite sandstone units, the present-day shelf and paleoshelf edge. For example, the deep-water fan, and growth-fault related sandstone reservoirs Rovuma River delta (fig. 6) contains turbidite sandstone (Ophir Energy Company (2011). units, and deep-water fan and growth-fault related sandstone The primary reservoir seals are Mesozoic and Cenozoic reservoirs (Ophir Energy Company, 2007, 2011; Law, 2011). drift and marginal-marine mudstone and shale. The Triassic to Jurassic syn-rift section contains structural Three generalized seismic cross sections drawn from \\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch12_figures\ch12_figures\ch12_figure06.ai traps related to graben and half-grabens with facies trapping onshore to offshore along the central coast of Tanzania are typical of rifts (Cope, 2000). Lower Cretaceous post-rift shown in figures 7 and 8 (Kejato, 2003). Seismic profiles have rocks (drift and passive margin) contain stratigraphic and imaged potential prospects in the offshore part of the Tanzania structural traps in transgressive and regressive sandstones, Coastal Province (Law, 2011; Ophir Energy, 2011). Geologic Model 9

Ruvu Basin - Zanzibar Channel - Deep Marine Makarawe-1 WEST EAST A A' Ruvu Zanzibar Pemba Deep Marine Davie FEET Basin High High Fracture SEA LEVEL 2,000 Seafloor 4,000 6,000 Tanga 8,000 Fault 10,000 12,000 Shoreline location unknown 0 10 20 KILOMETERS A A' 0 10 20 MILES

Line of section Dar es Salaam EXPLANATION

Top Eocene TANZANIA Top Upper Cretaceous INDIAN Top Lower Jurassic OCEAN Top Upper Permian Undated seismic horizon Seismic reflector Fault—Arrow shows relative motion INDEX MAP Makarawe-1 Dry hole with gas show and identifier

Figure 7. Generalized seismic cross section A–A‘ of the Ruvu and deep-marine basins and of the Zanzibar Channel, Tanzania. Modified from Kejato (2003). Not to scale.

1. Oil and gas was generated from Permian to Jurassic Exploration Karoo-age lacustrine and continental rocks (rift stage). The lacustrine rocks contain TOC values averaging At the time of this 2012 assessment, the province 4.0 to 5.0 weight percent. Early to Middle and Jurassic contained 5 gas fields (IHS Energy, 2009) and 3 new gas restricted marine rocks contain as much as 9 weight discoveries and is considered to be underexplored on the basis percent TOC, and Cretaceous rocks contain Type II of its exploration history. There have been some new discover- kerogen with as much as 12 weight percent TOC. ies since this assessment. The producing gas fields and recent Hydrocarbon generation of syn-rift Karoo-age source petroleum discoveries are limited to Cretaceous-Tertiary rocks most likely began in the Middle Jurassic, whereas offshore marine rocks. generation of the Middle Jurassic to Early Cretaceous Exploration wells and discovered accumulations on the syn-rift source rocks began in the Late Jurassic to continental shelf and upper slope (IHS Energy, 2009) provide Early Cretaceous. Generation of early post-rift sources evidence for the existence of an active petroleum system most likely began in the Late Cretaceous. The drift containing Mesozoic source rocks, the migration of hydrocar- and post-rift source rocks most likely began generating bons most likely since the Late Cretaceous, and the migration hydrocarbons in the Late Cretaceous. Hydrocarbon \\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch012_figures\ch12_figures\ch12_figure07.aiof the hydrocarbons into Cretaceous and Cenozoic reservoirs. generation most likely continues in the offshore parts of the assessment unit. Geologic Model 2. Hydrocarbons migrated into mostly Cretaceous and Paleogene reservoirs and traps. The geologic model developed for the assessment of conventional oil and gas in the Tanzania Coastal Province and 3. Hydrocarbon traps are mostly structural within the syn- the Coastal Plain and Offshore Assessment Unit, east Africa is rift rock units and both structural and stratigraphic in the as follows: postrift-rock units. 10 Assessment of Undiscovered Oil and Gas Resources of the Tanzania Coastal Province, East Africa

Ruvu Basin - Dar es Salaam - Deep Marine

WEST Ruvu Basin Dar Es Salaam Platform Kimbiji East-1 Coastal Basin EAST B Kiwangwa-1 Kisarawe-1 Kimbiji Main-1 Tancan-1 Latham B' FEET Island Coastline INDIAN OCEAN SEA LEVEL Seafloor 2,000 4,000 6,000 Pugu Major Bounding Uplift Coastal Tertiary 8,000 Fault Zone Fault Zone 10,000

Selous Basin - Mandawa Basin - Deep Marine

WEST Selous Basin Mandawa Salt Sub-Basin EAST C Liwale-1 C' 100 kilometers gap MBUO-1 Mandawa-7 Coastline FEET SEA LEVEL INDIAN OCEAN Seafloor 2,000 Masasi Spur 4,000 6,000 6,000 10,000

0 10 20 KILOMETERS

0 10 20 MILES Line of section B EXPLANATION Dar es Salaam Da Liwale-1 r es B' Salt P Sala latf am Well and identifier—Dry hole orm Top Eocene TANZANIA Top Upper Cretaceous INDIAN Line of section Top Lower Cretaceous MBUO-1 OCEAN Top Lower Jurassic Well and identifier—Oil show C Mandawa Salt Top Upper Permian Basin C' Undated seismic horizon Seismic reflector INDEX MAP Fault—Arrow shows relative motion Figure 8. Generalized seismic cross sections B–B‘, Ruvu and coastal basins and the Dar es Salaam Platform, Tanzania, and C–C‘, Selous, Mandawa, and deep-marine basins, Tanzania. Modified from Kejato (2003). Not to scale.

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch012_figures\ch12_figures\ch12_figure08.ai For Additional Information 11

4. The primary reservoir seals are Mesozoic and Cenozoic PETROLEUM mudstone and shale. SYSTEM EVENTS 5. The rifted passive margin analog (Charpentier and others,

2007) was used for assessment sizes and numbers because ACCUMULATION of similar source, reservoirs, and traps.

An events chart (fig. 9) for the Mesozoic-Cenozoic MIGRATION- petroleum systems and the Mesozoic-Cenozoic Reservoirs AU ROCK UNITS RESERVOIR ROCKS

OVERBURDEN ROCKS PRESERVATION

summarizes the age of the source, seal, and reservoir rocks and Age in million years (Ma) SOURCE ROCKS SEAL ROCKS TRAP FORMATION GENERATION- the timing of trap development and generation, and migration 0 Plio of hydrocarbons. Neogene Mio 23 Olig Resource Summary Paleogene Eoc 50 Using a geology-based assessment, the U.S. Geological Pal Survey estimated mean volumes of undiscovered, technically 65 recoverable conventional oil and gas resources for the L Mesozoic-Cenozoic Reservoirs Assessment Unit in the Tanzania Coastal Province (table 1). The mean volumes Cretaceous 100 are estimated at 2,806 million barrels of oil, 71,107 billion cubic feet of gas, and 2,212 million barrels of natural gas E liquids. The estimated mean size of the largest oil field that is expected to be discovered is 594 million barrels of oil, and the estimated mean size of the expected largest gas field is 146 6,162 billion cubic feet of gas. For this assessment, a minimum 150 L undiscovered field size of 5 million barrels of oil equivalent was used. No attempt was made to estimate economically M Jurassic recoverable reserves. E 200 200 Acknowledgments L The author wishes to thank Mary-Margaret Coates, Triassic Jennifer Eoff, Christopher Schenk, and David Scott for M E their suggestions, comments, and editorial reviews, which 250 251 L greatly improved the manuscript. The author thanks Permian Wayne Husband for his numerous hours drafting many of E the figures used in this manuscript, and Chris Anderson, who supplied the Geographic Information System files for Figure 9. Events chart for the Mesozoic-Cenozoic Composite this assessment. Total Petroleum System (727301) and the Mesozoic-Cenozoic Reservoirs Assessment Unit (72730101). Gray, rock units present; yellow, age range of reservoir rock; green, age ranges of source, seal, and overburden rocks and the timing of trap formation and For Additional Information generation, and migration and preservation of hydrocarbons; wavy line, unconformity. Divisions of geologic time conform to dates Assessment results are available at the USGS Central in U.S. Geological Survey Fact Sheet 2010–3059 (U.S. Geological Energy Resources Science Center website: http://energy.cr.usgs. Survey Geologic Names Committee, 2010). Ma, million years ago; gov/oilgas/noga/ or contact Michael E. Brownfield, the assessing Plio, Pliocene; Mio, Miocene; Olig, Oligocene; Eoc, Eocene; Pal, geologist ([email protected]).\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den13_cmrm00_0129_ds_brownfield\dds_69_gg_ch12_figures\ch12_figures\ch12_figure09.aiPaleocene, L, Late; E, Early; M, Middle; ?, uncertain. 12 Assessment of Undiscovered Oil and Gas Resources of the Tanzania Coastal Province, East Africa

Table 1. Tanzania Coastal Province 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 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 Tanzania Coastal-Mesozoic-Cenozoic Composite TPS Oil 594 1,223 2,608 5,064 2,806 1,583 3,555 7,571 3933 42 95 208 106 Mesozoic-Cenozoic Reservoirs AU Gas 6,162 35,902 64,054 108,925 67,174 1,118 2,006 3,433 2,106 Total Conventional Resources 1,223 2,608 5,064 2,806 37,485 67,609 116,496 71,107 1,160 2,101 3,641 2,212

References Mbede, E.I., and Dualeh, A., 1997, The coastal basins of Somalia, Kenya, and Tanzania, in Selley, R.C., ed., Vol- Charpentier, R.R., Klett, T.R., and Attanasi, E.D., 2007, ume 3, African basins—Sedimentary basins of the world: Database for assessment unit-scale analogs (exclusive of the Amsterdam, Elsevier Science B. V., p. 211–233. United States) Version 1.0: U.S. Geological Survey Open- Ophir Energy Company, 2007, Hydrocarbon prospectivity of File Report 2007–1404, 36 p., CD–ROM. deepwater southern Tanzania: East African Petroleum Con- Cope, Michael, 2000, Tanzania’s Mafia deepwater basin indi- ference, Arusha, Tanzania, March 7–9, 2007, 26 p. cates potential on new seismic data: Oil and Gas Journal, Ophir Energy Company, 2011, Exploration in Tanzania and v. 98, no. 33. Available at http://www.ogj.com/articles/ Madagascar: Evolution Securities East Africa Conference, print/volume-98/issue-33/exploration-development/ tanzanias-mafia-deepwater-basin-indicates-potential-on- London, January 13, 2011, 27 p. new-seismic-data.html. Last accessed February 28, 2013. Reeves, C.V., Sahu, B.K., and de Wit, M., 2002, A re-examination Fugro Multi Client Services, 2010, New Seychelles, of the paleo-position of Africa’s eastern neighbours in Gond- non-exclusive 2D seismic survey: Available at http:// wana: Journal of African Earth Sciences, v. 34, no. 1, www.fugromcs.com.au/Fliers/Flier_Seychelles.pdf. p. 101–108. Accessed March 6, 2012, Rusk, Bertagne & Associates, 2003, Petroleum geology and IHS Energy, 2009, International petroleum exploration and geophysics of the Mozambique Channel, executive sum- production database [current through December 2009]: mary: Available at http://www.petrocommunicators.com/ Available from IHS Energy, 15 Inverness Way East, Engle- moz/index.htm. Accessed March 6, 2012. wood, Colo. 80112, USA. U.S. Geological Survey Geologic Names Committee, 2010, Kagya, M.L.N., 1996, Geochemical characterization of Trias- Divisions of geologic time: U.S. Geological Survey Fact sic petroleum source rock in the Mandawa basin, Tanzania: Journal of African Earth Sciences, v. 23, no. 1, p. 73–88. Sheet 2010−3059, 2 p. Available at http://pubs.usgs.gov/ fs/2010/3059/. Kejato, Kejo, 2003, The geology and petroleum potential of Tanzania: Dar es Salaam, Tanzania, Tanzania Petroleum U.S. Geological Survey World Conventional Resources Development Corporation, 29 p. Assessment Team, 2012, An estimate of undiscovered Law, Carol, 2011, Northern Mozambique—True “wildcat” conventional oil and gas resources of the world, 2012: exploration in east Africa: American Association of Petroleum U.S. Geological Survey Fact Sheet 2012–3042, 6 p. Geologists Search and Discovery article 110157 (2011), 39 p. Available at http://pubs.usgs.gov/fs/2012/3042/.

M ED ATLANTIC ITE RRAN OCEAN EAN SEA

INDIAN OCEAN

Tanzania Coastal

SOUTH ATLANTIC OCEAN

INDIAN OCEAN

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