assessment of undiscovered oil and gas resources of the ...4 assessment of undiscovered oil and gas...

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

By Michael E. Brownfield

Digital Data Series 69–GG

U.S. Department of the InteriorU.S. Geological Survey

Chapter 10 ofGeologic Assessment of Undiscovered Hydrocarbon Resources of Sub-Saharan AfricaCompiled by Michael E. Brownfield

ATLANTIC OCEAN

SOUTHATLANTIC

OCEAN

INDIAN OCEAN

INDIAN OCEAN

MEDITERRANEAN SEA

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MozambiqueCoastal

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U.S. Department of the InteriorSALLY JEWELL, Secretary

U.S. Geological SurveySuzette 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 Mozambique 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.10, 13 p., http://dx.doi.org/10.3133/ds69GG.

ISSN 2327-638X (online)

http://www.usgs.gov

http://www.usgs.gov/pubprod/

http://dx.doi.org/10.3133/ds69GG

iii

Contents

Abstract ...........................................................................................................................................................1Introduction.....................................................................................................................................................1Tectonic History and Geology of Mozambique Coastal Province, East Africa ....................................4Petroleum Occurrence in Mozambique Coastal Province, East Africa ................................................4

Source Rocks.........................................................................................................................................4Reservoirs, Traps, and Seals ...............................................................................................................7

Exploration ......................................................................................................................................................9Geologic Model ............................................................................................................................................11Resource Summary .....................................................................................................................................11For Additional Information ..........................................................................................................................12Acknowledgments .......................................................................................................................................12References ....................................................................................................................................................12

Figures

1. Map showing Mozambique Coastal Province, Mesozoic-Cenozoic Reservoirs Assessment Unit, Mozambique Channel area, and the Ruvuma Delta 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. Generalized stratigraphic columns of Coastal Mozambique, Mozambique

Channel, and Coastal Tanzania, Coastal Morondava Basin, and the Seychelles ..............6 5. Schematic cross section of the Rovuma River delta, northern Mozambique ....................7 6. Stratigraphic column for the onshore and projected offshore parts of the

Rovuma Basin, northern Mozambique ......................................................................................8 7. Cross section across the Mozambique Channel and the Morondava Basin

showing the top of the oil and gas windows ............................................................................9 8. Schematic cross section of the Zambezi Delta, Mozambique ............................................10 9. Events chart for the Mesozoic-Cenozoic Petroleum System (734301) and the

Mesozoic-Cenozoic Reservoirs Assessment Unit (73430101) .............................................11

Table

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

iv

Abbreviations Used in This Reportkm2 square kilometer

AU assessment unit

TOC total organic carbon

TPS total petroleum system

USGS U.S. Geological Survey

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

By Michael E. Brownfield

Generation of hydrocarbons from drift and post-rift sources began in the Late Cretaceous and, in parts of the offshore, continues today. Hydrocarbons migrated into Cretaceous and Paleogene reservoirs and traps. Traps are mostly structural within the syn-rift section and are both structural and stratigraphic in the post-rift rock units. The primary seals are Mesozoic and Cenozoic mudstone and shale. Rifted passive margin analog was used for assessment sizes and numbers because of similar source, reservoirs, and traps.

The U.S. Geological Survey estimated mean volumes of undiscovered, technically recoverable conventional oil and gas resources for the Mesozoic-Cenozoic Reservoirs Assessment Unit in the Mozambique Coastal Province. The mean volumes are estimated at 11,682 million barrels of oil, 182,349 billion cubic feet of gas, and 5,645 million barrels of natural gas liquids. The estimated mean size of the largest oil field that is expected to be discovered is 1,041 million barrels of oil and the estimated mean size of the expected largest gas field is 7,976 billion cubic feet of gas. For this assessment, a minimum undiscovered field size of 5 million barrels of oil equivalent was used. No attempt was made to estimate economically recoverable reserves.

Introduction

The main objective of the U.S. Geological Survey’s (USGS) National and Global Petroleum Assessment Project is to assess the potential for undiscovered, technically recover-able oil and natural gas resources of the United States and the world (U.S. Geological Survey World Conventional Resources Assessment Team, 2012). As part of this program, the USGS completed an assessment of the Mozambique Coastal Province in 2011 (fig. 1), an area of approximately 648,650 square kilometers (km2). The Mozambique Province contains rift, rift-sag, passive-margin, and drift rocks of Paleozoic to Holocene age. This assessment was based on data from oil and gas exploration wells, discovered and producing fields (IHS Energy, 2009), and published geologic reports. Generalized geology of east Africa is shown in figure 2.

AbstractThe main objective of the U.S. Geological Survey’s

National and Global Petroleum Assessment Project is to assess the potential for undiscovered, technically recoverable oil and natural gas resources of the United States and the world. As part of this project, the U.S. Geological Survey completed an assessment of the Mozambique Province in 2011, an area of approximately 648,650 square kilometers. The Mozambique Province contains rift, rift-sag, passive-margin, and drift rocks of Paleozoic to Holocene age. This assessment was based on data from oil and gas exploration wells and published geologic reports.

The Mozambique Province is a priority province for the World Petroleum Assessment and was assessed in 2011 because of increased exploratory activity and increased interest in its future oil and gas resource potential. The assessment was geology based and used the total petroleum system concept. The geologic elements of a total petroleum system consist of hydrocarbon source rocks (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 Composite Total Petroleum System with one assessment unit, the Mesozoic-Cenozoic Reservoirs Assessment Unit, an area of approximately 464,420 square kilometers. At the time of the assessment, the Mozambique Coastal Province contained only two gas accumulations exceeding the minimum size of 30 billion cubic feet of gas; the province is considered to be underexplored on the basis of its exploration history.

Oil and gas were generated from Permian to Paleogene source rocks. Jurassic Karoo-age lacustrine and continental rocks source rocks average 4.0 to 5.0 weight percent total organic carbon. Lower to Middle Jurassic restricted marine rocks contain as much as 9 weight percent organic carbon, and Cretaceous Type II source rocks contain as much as 12 weight percent organic carbon. Hydrocarbon generation of syn-rift Karoo-age sources began in the Middle Jurassic, whereas the generation from Middle Jurassic to Early Cretaceous syn-rift sources began in the Late Jurassic to Early Cretaceous.

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

Figure 1. Locations of the Mozambique Coastal Province, Mesozoic-Cenozoic Reservoirs Assessment Unit, Mozambique Channel area, and the Ruvuma Delta along the central coast of East Africa. (Stratigraphic columns for the Mozambique Channel and Rovuma Delta are shown in figures 4 and 6.)

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MozambiqueCoastal

7343

AFRICA

INDEX MAP

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

0 150 300 KILOMETERS

0 300 MILES150

Réunion

MAURITIUS

COMOROSMayotte

ZAMBIA

MALAWI

ZIMBABWE

LESOTHO

SWAZILAND

SOUTHAFRICA

KENYA

BURUNDI

RWANDA

70°E66°E62°E58°E54°E50°E46°E42°E38°E34°E30°E

2°S

6°S

10°S

14°S

18°S

22°S

26°S

30°S

34°S

TANZANIA

MADAGASCAR

MOZAMBIQUE

SEYCHELLES

INDIAN OCEAN

RovumaDelta

Mesozoic-Cenozoic Reservoirs Assessment Unit boundary

EXPLANATIONMozambique Coastal Province boundary

Gas field

Mozambique Coastal7343

Introduction 3

Figure 2. Generalized geology of East Africa. Modified from Ophir Energy Company (2011).

CongoBasin

TANZANIA

KalahariBasin

Beira

MAPUTO

Dar es Salaam

MOGADISHU

Somali OceanicBasin

Continent-oceanicboundary

(COB)

OgadenBasin

RovumaDeltaDavie Fracture Zone

Moz

ambiq

ue C

hann

el

Aswa Shear Zone

Cupa Fault Zone1,0

00

KarrooBasin

Continent-oceanicboundary

(COB)

MandawaBasin

MajungaBasin

MorondavaBasin

MozambiqueBasin

INDIAN OCEAN

MA

DA

GA

SCA

R

Mombasa

0 200 400 600 KILOMETERS

0 600 MILES200 400

EXPLANATION

Bathymetric contour, 1,000 meter line—Location approximate

Continental crust—Palo fill

Permian-Triassic–Early Jurassic—Karoo-age rock

Phanerozoic—Intracratonic basin

ContactFault or fault zone—Dashed where approximate. Arrows show relative motion

Post Early Jurassic—Passive margin basin

Tertiary—Volcanic province

Undifferentiated—Precambrian basement

Graben—Teeth on downthrown side

MOZAMBIQUE

Tsimiro

roFie

ld


The Mozambique Province, which was a priority province for the World Petroleum Assessment, was assessed in 2011 because of increased energy exploration activity and increased interest in its future oil and gas resource potential. The assessment was geology based and used the total petroleum system concept. The geologic elements of a total petroleum system include hydrocarbon source rocks (source-rock maturation and hydrocarbon generation and migration), reservoir rocks (quality and distribution), and traps for hydrocarbon accumulation. Using these geologic criteria, the USGS defined the Mesozoic-Cenozoic Composite Total Petroleum System (TPS) with one assessment unit, the Mesozoic-Cenozoic Reservoirs Assessment Unit (AU) (fig. 1), an area of approximately 464,420 km2. The total petroleum system was defined to include Mesozoic to Paleogene lacustrine and marine source rocks and conventional reservoirs.

Tectonic History and Geology of Mozambique Coastal Province, East Africa

The Mozambique Coastal Province is directly related to the breakup of Gondwana (fig. 3) in the late Paleozoic and Mesozoic (Coster and others, 1989; Reeves and others, 2002; Rusk, Bertagne & Associates, 2003). The province developed in four phases: (1) a pre-rift stage that started during the Carboniferous during which a mantle plume caused uplift, extension, microplate formation, rifting, and volcanism; (2) a syn-rift phase that started during the Permo-Triassic and continued into the Jurassic, which formed grabens and half-grabens and the deposition of possible lacustrine and continental source rocks; (3) a syn-rift–drift phase that began in the Middle Jurassic and continued into the Paleogene, depositing sediments of marine clastic rocks and carbonate and, during periods of restricted-marine conditions, depositing sediments of marine source rocks; and (4) a passive-margin phase that began in the late Paleogene and continues to the present (Envoi—Energy Venture Opportunities International, 2011). The stratigraphic section present in Mozambique Coastal Province is generally the same as the section present in the coastal Morandava Basin, coastal Tanzania, and the Seychelles (figs. 2, 4) (Rusk, Bertagne & Associates, 2003).

The opening of the Indian Ocean began in the Permian and continued into the Jurassic during the syn-rift stage (Reeves and others, 2002). In the Middle Jurassic, Madagascar, India, and north Mozambique separated from Africa (fig. 3) and formed a passive margin and a

carbonate platform that was later covered by Upper Jurassic to Cretaceous marine deposits (figs. 4, 5). During the mid-Cretaceous the passive margin basin again became the site for deposition of open-marine sediments.

A stratigraphic column for the offshore and onshore parts of the Rovuma Basin and Delta along the northern part of Mozambique is shown in figure 6. Since 2006 and the 2011 assessment, several new hydrocarbon discoveries have been found in the offshore part of the delta (Law, 2001; IHS Energy, 2009; IHS Energy, 2012). Three generalized seismic cross sections drawn from onshore to offshore are shown in figures 5, 7, 8. These seismic profiles have imaged potential source rock units and prospects in the offshore parts of northern Mozambique (Law, 2001; Ophir Energy Company, 2011).

Petroleum Occurrence in Mozambique Coastal Province, East Africa

Source Rocks

The Mesozoic-Cenozoic Composite Total Petroleum System was defined to include Mesozoic to Paleocene source rocks and conventional reservoirs (fig. 4). The Permian to Triassic section contains fluvial and lacustrine source rocks averaging 5 to 6 weight percent total organic carbon (TOC); some samples have as much as 17.4 weight percent TOC (Envoi—Energy Venture Opportunities International, 2011). The Lower to Middle Jurassic contains restricted marine Type II kerogen source rocks, marginal marine and deltaic Types II and III kerogen source rocks, and Type I lacustrine source rock (Cope, 2000; Rusk, Bertagne & Associates, 2003). The offshore part of Ruvuma Delta contains Early to Middle Jurassic restricted marine Type II source rocks with TOC contents as much as 12 weight percent (Cope, 2000). Late Jurassic to Early Cretaceous marlstone contains Type II and Type III kerogen with as much as 5 weight percent TOC (Envoi—Energy Venture Opportunities International, 2011). Ophir Energy Company (2007) reports that Aptian shale with TOC contents as much as 9 weight percent. Upper Cretaceous marine sources contain Type II and Type III kerogen with TOC contents as much as 7.4 weight percent and Eocene sources contain Type II and Type III kerogen with TOC contents as much as 12.1 weight percent (Cope, 2000). These source rocks have been found in the Ruvuma Delta in northern Mozambique and southern Tanzania.

Petroleum Occurrence in Mozambique Coastal Province, East Africa 5

Figure 3. Reconstruction of the early breakup of Gondwana during the Early Jurassic (200 Ma). Modified from Reeves and others (2002).

0 100 200 KILOMETERS

0 200 MILES100

HORN OF AFRICA

KENYA

TANZANIA

MADAGASCAR

INDIA

INDIA

SRI LANKA

EAST ANTARCTICA

SEYCHELLES

Mik

ume

Rift

Cambay Rift

Saurastra

Anza Rift

Narmada-Son

Basin

NORT

HM

OZA

MBI

QUE

Selous

Line of latitude or longitude— Oriented as on modern map

EXPLANATION

Precambrian crustal fragment

Rift-related rock



EXPLANATION

Sandstone

Sandstone and conglomerate

Shale

Sandy shale

Calcareous shaley marlstone

Limestone Reservoir rock, East Africa

Salt

Igneous rock—Extrusive

Igneous rock—Oceanic crust

Basement

Unconformity

Contact—Dashed where location approximate

Extent uncertain

R

Source rock

Potential reservoirOil fieldGas field

CoastalMozambique

Tectonicevents

Tectonicevents

Mozambique Channeland Coastal Tanzania

CoastalMorandava Basin

Envir. Envir.W W

TERT

IARY

CRET

ACEO

USJU

RASS

ICTR

IASS

ICPE

RMIA

NCA

RBON

-IF

EROU

SPR

ECAM

-BR

IAN

Basement

Neo

gene

Pale

ogen

eUp

per

Low

erUp

per

Uppe

rM

ML

UL

Mid

dle-

Uppe

rLo

wer

FluvialDeltaic

Deltaic

Marine

?

?

?

Cont

inen

tal w

ith m

inor

mar

gina

l mar

ine

Zone

s o

f re

serv

oir

pote

ntia

l

Mar

ine

Mar

ine

Cont

inen

tal w

ith m

inor

mar

gina

l mar

ine

Shallowmarine

Deltaic tocont.

Shal

low

mar

ine

to c

ontin

enta

l

Shal

low

mar

ine

lago

onal

toco

ntin

enta

l

Mar

gina

l sag

and

pas

sive

mar

gin

Rift,

mar

gina

l sag

and

drift

Mar

gina

l sag

and

drif

t

Rift

and

mar

gina

l sag

Recu

rren

t rift

ing

and

uplif

t

Recu

rren

t rift

ing

and

uplif

t

Seyc

helle

s-In

dia

brea

kup

Mad

agas

car-

Seyc

helle

s-In

dia

brea

kup

from

Afri

ca

Mad

agas

car-

Seyc

helle

s-In

dia

brea

kup

from

Afri

ca

Rest

ricte

d m

arin

e, o

pen

mar

ine,

and

mar

gina

l mar

ine

Seychelles

SeychellesEast Africa

Drift

Rift

Lithology

?

?

?

Lithology Lithology Lithology

?

?

?

?

?

W EEE

?Re

stric

ted

mar

ine,

shal

low

mar

ine,

and

ope

n m

arin

eSh

allo

w m

arin

e an

d op

en m

arin

eCo

ntin

enta

l with

min

or m

argi

nal m

arin

e

Envir.

R

R

R

R

R

R

R

R

Age

Rifti

ng a

ndm

argi

nal s

ag

Figure 4. Generalized stratigraphic columns of Coastal Mozambique, Mozambique Channel and Coastal Tanzania, Coastal Morondava Basin, and the Seychelles along the east coast of Africa (fig. 1). W, west; E, east; Envir., environment; cont., continental; L, Lower; M, Middle; U, Upper. Modified from Rusk, Bertagne & Associates (2003) and PetroSeychelles (2013).

Petroleum Occurrence in Mozambique Coastal Province, East Africa 7

Rovuma onshore Rovuma offshore

Caravel

Caravel

Ironclad

Jurassic

Cretaceous

Tertiary

EXPLANATION

NOT TO SCALE


WEST EAST

INDIAN OCEAN

Mecupa Windjammer

Sandstone reservoir rock—Turbidite sandstone unit, deep water fan, and growth-fault-related sand

Carbonate

Basement

Contact

FaultFault—Growth fault, normal fault, and thrust fault

Drill hole and identifier—Approximate depth to target depth

Figure 5. Schematic cross section of the Rovuma River delta, northern Mozambique. Modified from Law (2011). Not to scale.

Oil and gas generation most likely began in the Early Cretaceous for the Upper Jurassic syn-rift sources in the province (Coster and others, 1989). Oil and gas generation began in the Late Cretaceous for the Barremian to Aptian post-rift sources and in the offshore parts of the province the Late Cretaceous post-rift sources began oil and gas generation began in the early Paleogene and is most likely continu-ing today (Coster and others, 1989; Envoi—Energy Venture Opportunities International, 2011). Oil- and gas-generation windows are shown in figure 7 for the Mozambique Channel and the Morondava Basin (Envoi—Energy Venture Opportunities International, 2011).

Reservoirs, Traps, and Seals

The Mozambique Coastal Province and the Mesozoic-Cenozoic Reservoirs Assessment Unit (fig. 1) contain Mesozoic and Cenozoic clastic reservoirs (Coster and others, 1989; Nairn and others, 1991; Cope, 2000; Rusk, Bertagne

& Associates, 2003; Law, 2011). Triassic to Middle Jurassic syn-rift rocks contain possible alluvial fans, fan deltas, fluvial deltas, and lacustrine sandstones reservoirs. The Late Jurassic post-rift rocks contain reef and platform carbonate rocks that are potential reservoirs. The post-rift Cretaceous rocks contain regressive and transgressive marine sandstone, slope-turbidite sandstone and basin-floor fan sandstone reservoirs (Coster and others, 1989). Upper Cretaceous and Cenozoic passive-margin rocks contain possible carbonate reservoirs and Maastrichtian and Paleocene turbidite and basin-floor fan reservoirs (Cope, 2000). Volcanic rocks found within the Karoo age rocks and Cretaceous section may have degraded some of the reservoirs.

The Mesozoic-Cenozoic Reservoirs Assessment Unit (fig. 1) contains sandstone reservoirs that mostly are associated with growth-fault-related structures such as rotated fault blocks within the continental shelf, deep water fans, turbidite sandstone units, and slope truncations along the present-day shelf and paleoshelf edge (Cope, 2000; Rusk, Bertagne & Associates, 2003; Law, 2011). For example, the Rovuma River delta (fig. 5) contains turbidite sandstone units,



Period Epoch Stage Onshore OffshoreWest EastQuaternary Pleistocene

Cen

ozoi

cM

esoz

oic

Pal

eoge

neC

reta

ceou

sJu

rass

icN

eoge

ne

Pliocene

Miocene

Oligocene

Eocene

CalabrianPiacenzian

ZanclianMessinianTortonian

SerravallianLanghian

BurdigalianAquitanian

Chattian

RupelianPriabonianBartonian

Lutetian

Campanian

SantonianConiacianTuronian

Cenomanian

Albian

Aptian

Barremian

Hauterivian

Valanginian

Berriasian

TithonianKimmeridgian

Oxfordian

Callovian

Bathonian

Bajocian

Aalenian

YpresianThanetianSelandian

Danian

Maastrichtian

Paleocene

Middle

Late

Late

Early

?Chinda

FormationMikindani Formation Rovuma Delta Complex

Pemba Formation

Rovuma Delta Complex

Mifume Formation

Macomia Formation

Pemba Formation

Alto Jingone FormationAlto Jingone Formation

UnconformityPresent coastline

EXPLANATION

Sandstone Continentalclastic rock

Conglomerate

Paralic clastic rock

Marine sandstone

Marine shale, siltstone, and sandstone

Calcareous sandstone

Shelf carbonate

Marl

Contact

Quissanga Formation

Figure 6. Stratigraphic column for the onshore and projected offshore parts of the Rovuma Basin, northern Mozambique. Middle and Lower Jurassic units shown in figure 4, such as the Lower Jurassic salt, are not shown. Modified from Key and others (2008).

Exploration 9

Figure 7. Cross section across the Mozambique Channel and the Morondava Basin (line of section on index map) showing the top of the oil- and gas-generation windows. Cross section is approximately 420 kilometers long, not to scale. Modified after Envoi—Energy Venture Opportunities International (2011).


INDEX MAP

WEST-NORTHWEST EAST-SOUTHEAST

KILOMETERSSEA LEVEL

4

6

8

10

2

EXPLANATION

Cenozoic

Tertiary

Upper Cretaceous

Lower Cretaceous

Jurassic

Oil field andidentifier

Gas field andidentifier

Triassic to Permian

Basement rock

Volcanic

ContactFault

MnaziBay Field(Offset to

South)

MnaziBay Field

X'

MOZAMBIQUE MADAGASCAR

Île Juan de NovaExclusive Economic Zone

FRENCH SOUTHERN ANDANTARCTIC LANDS

X

IroncladDiscovery(Offset to

North) WindjammerDiscovery(Offset to

North)Manambolo

Gas FieldJuan deNova Island

Shallow anddeepwaterprospect

TsimiroroHeavy Oil

Field BemolangaTar Sands

Top of Oil Window

Top of Gas Window

Davie Fracture Zone Morondava Basin

IroncladDiscovery

MOZAM

BIQUE

MA

DA

GA

SCA

R

MALAWI

Moz

ambiq

ue

Chann

el

RovumaDelta

Majunga Basin

Mor

onda

va B

asin

Mozambique Channel

INDIANOCEAN

X'

X

Line of section

deep-water fan, and growth-fault-related sandstone reservoirs (Law, 2011). A seismic profile reported by Walford and others (2005) interpreted the Late Cretaceous and Cenozoic section showing the Domo Sandstone, a potential reservoir and clinoform packages, channeling, slumping, and growth faults in the offshore part of the Zambezi Delta (fig. 8).

Triassic to Jurassic syn-rift rocks contains structural traps related to graben and half grabens. Lower Cretaceous post-rift rocks (drift and passive-margin) contain stratigraphic traps such as transgressive and regressive sandstones and structural traps including salt structures, drape anticlines, and flower structures (Rusk, Bertagne & Associates, 2003; Law, 2011). Upper Cretaceous and Paleogene post-rift rocks (drift and passive-margin) contain both structural and stratigraphic traps in growth-fault-related structures, rotated fault blocks within the continental shelf, deep-water fans, turbidite units, and slope truncations along the present day shelf and paleoshelf edge.

The primary reservoir seals are Mesozoic and Cenozoic drift and marginal-marine mudstone and shale (Nairn and others, 1991; Cope, 2000). Secondary fault-related seals are

found in Karoo-age grabens and Mesozoic half-grabens, faulted drape anticlines, and inversion-related anticlines (Cope, 2000; Rusk, Bertagne & Associates, 2003).

Exploration

At the time of the 2011 assessment, the Mozambique Province contained five gas fields and no oil fields (IHS Energy, 2009) and is considered to be underexplored on the basis of its limited exploration activity. Recent hydrocarbon shows are limited to the Cretaceous-Tertiary offshore drift and passive-margin section (Law, 2011).

Hydrocarbon shows in exploration wells on the continental shelf and upper slope provide evidence for the existence of an active petroleum system containing Mesozoic source rocks and for the migration of the hydrocarbons into Cretaceous and Cenozoic reservoirs, most likely since the Late Cretaceous.



INDEX MAP

0

1

3

4

5

2

Well and identifierWell A

A'

Tertiary

Cretaceous

Fault

Jurassic

ContactSeismic reflector

EXPLANATION

AWell A Well B

Top Eocene

Domo Sandstonechanneling

slumping

Seafloor

TWO WAYTIME IN

SECONDS

Top PlioceneTop Miocene

Middle MioceneTop Oligocene

Top Cretaceous

0 5 10 KILOMETERS

0 10 MILES 5

Zambezi River

INDIAN OCEAN

INDIANOCEAN

BeiraA'

A

MOZAMBIQUE

Line of section

Figure 8. Schematic cross section of the Zambezi Delta, Mozambique. Modified from Walford and others (2005).

Resource Summary 11

Figure 9. Events chart for the Mesozoic-Cenozoic Total Petroleum System (734301) and the Mesozoic-Cenozoic Reservoirs Assessment Unit (73430101) in the Mozambique Coastal Province, South Africa. Gray, rock units present; yellow, age range of reservoir rocks; green, age ranges of source and overburden rocks, timing of trap formation, and generation, migration, and preservation of hydrocarbons; wavy line, unconformity. Divisions of geologic time conform to dates in U.S. Geological Survey Geologic Names Committee (2010). Ma, thousands of years ago; Plio, Pliocene; Mio, Miocene; Olig, Oligocene; Eoc, Eocene; Pal, Paleocene; L, Late; E, Early; M, Middle; ?, uncertain.


Deltaic

Delta

ic

Rift

Cont

inen

tal

Restr

icted

and

open

mar

ineOp

en a

nd m

argi

nal m

arin

e

Marine

PETROLEUMSYSTEM EVENTS

Age in million years (Ma)

0

100

200

50

150

250

Paleogene

Cretaceous

Jurassic

Triassic

Permian

65

146

200

251

E

E

E

M

M

LE

L

L

L

Neogene

23

Pal

Eoc

Olig

Mio

Plio

PRES

ERVA

TIO

N

GEN

ERA

TIO

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Geologic ModelThe geologic model developed for the assessment of

conventional oil and gas in the Mozambique Coastal Province and the Coastal Plain and Offshore Assessment Unit is as follows:

1. Oil and gas was generated from Permian to Jurassic Karoo-age lacustrine and continental rocks (rift stage). The lacustrine rocks contain TOC values averaging 4.0 to 5.0 weight percent. Early to Middle and Jurassic restricted marine rocks contain as much as 9 weight percent TOC, and Cretaceous marine rocks contain Type II kerogen with as much as 12 weight percent TOC. Generation of hydrocarbons in syn-rift Karoo-age source rocks most likely began in the Middle Jurassic, whereas generation of hydrocarbons in Middle Jurassic to Early Cretaceous syn-rift source rocks began in the Late Jurassic to Early Cretaceous. Generation of early post-rift sources most likely began in the Late Cretaceous. The drift and post-rift source rocks most likely began generating hydrocarbons in the Late Cretaceous. Hydrocarbon generation most likely continues today in the offshore parts of the assessment unit.

2. Generated hydrocarbons migrated into mostly Cretaceous and Paleogene sandstone reservoirs.

3. Hydrocarbon traps are structural within the syn-rift rock units and are both structural and stratigraphic in the post-rift rock units.

4. The primary reservoir seals are Mesozoic and Cenozoic mudstone and shale.

5. The rifted passive margin analog (Charpentier and others, 2007) was used for assessment sizes and numbers because of similar source, reservoirs, and traps.

An events chart (fig. 9) for the Mesozoic-Cenozoic Composite TPS and the Mesozoic-Cenozoic Reservoirs AU summarizes the age of the source, seal, and reservoir rocks and the timing of trap development, generation, and migration.

Resource SummaryAt the time of this 2011 assessment, the Mozambique

Coastal Province contained only five gas accumulations exceeding the minimum size of 30 billion cubic feet of gas; this province is considered to be underexplored on the basis of its level of exploration activity. Using a geology-based assessment, the USGS estimated mean volumes of undiscov-ered, technically recoverable conventional oil and gas resources for the Mesozoic-Cenozoic Reservoirs Assessment Unit in the Mozambique Coastal Province (table 1). The mean volumes are estimated at 11,682 million barrels of oil, 182,349 billion cubic feet of gas, and 5,645 million barrels of natural gas liquids. The estimated mean size of the largest oil


field that is expected to be discovered is 1,041 million barrels of oil and the estimated mean size of the expected largest gas field is 7,976 billion cubic feet of gas. For this assessment, a minimum undiscovered field size of 5 million barrels of oil equivalent was used. No attempt was made to estimate economically recoverable reserves.

For Additional InformationAssessment results are available at the USGS

Central Energy Resources Science Center website: http://energy.cr.usgs.gov/oilgas/noga/ or contact Michael E. Brownfield, the assessing geologist ([email protected]).

AcknowledgmentsThe author wishes to thank Mary-Margaret Coates,

Jennifer Eoff, Christopher Schenk, and David Scott for their suggestions, comments, and editorial reviews, which greatly improved the manuscript. The author thanks Wayne Husband for his numerous hours drafting many of the figures used in this manuscript, and Chris Anderson, who supplied the Geographic Information System files for this assessment.

References

Charpentier, R.R., Klett, T.R., and Attanasi, E.D., 2007, Database for assessment unit-scale analogs (exclusive of the United States) Version 1.0: U.S. Geological Survey Open-File Report 2007–1404, 36 p., CD–ROM.

Cope, M., 2000, Tanzania’s Mafia deepwater basin indicates potential on new seismic data: Oil and Gas Journal, v. 98, issue 33, 6 p., http://www.ogj.com/articles/print/volume-98/issue-33/exploration-development/tanzanias-mafia- deepwater-basin-indicates-potential-on-new-seismic- data.html. Last accessed February 28, 2013.

Table 1. Mozambique 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]

Total Petroleum Systems (TPS) and Assessment Units (AU)

Field type

Largest expected

mean field size

Total undiscovered resourcesOil (MMBO) Gas (BCFG) NGL (MMBNGL)

F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean

Mozambique Coastal-Mesozoic-Cenozoic Composite TPS

Mesozoic-Cenozoic Reservoirs AU Oil 1,041 6,268 11,174 18,857 11,682 8,423 15,615 27,238 16,425 225 421 744 444Gas 7,976 93,486 158,654 263,301 165,924 2,915 4,978 8,270 5,201

Total Conventional Resources 6,268 11,174 18,857 11,682 101,909 174,269 290,539 182,349 3,140 5,399 9,014 5,645

Coster, P.W., Lawrence, S.R., and Fortes, G., 1989, Mozambique—A new geological framework for hydro-carbons exploration: Journal of Petroleum Geology v. 12, no. 2, p. 205–230.

Envoi—Energy Venture Opportunities International, 2011, Mozambique Channel (offshore S.E. Africa), Juan de Nova Est Permit, Morondava Basin: Envoi Limited, London, http://envoi.co.uk/wp-content/uploads/2012/11/P191 WessexSEAfricaJuanDeNovaSynopsis.pdf. Accessed March 20, 2013.

IHS Energy, 2009, International petroleum exploration and production database [current through December 2009]: Available from IHS Energy, 15 Inverness Way East, Englewood, Colo. 80112 USA.

IHS Energy, 2012, International petroleum exploration and production database [current through December 2009]: Available from IHS Energy, 15 Inverness Way East, Englewood, Colo.

Key, R.M., Smith, R.A., Smelror, M., Saether, O.M., Thorsnes, T., Powell, J.H., Njange, F., and Andamela, E.B., 2008, Revised lithostratigraphy of the Mesozoic-Cenozoic succession of the onshore Rovuma Basin, northern coastal Mozambique: South African Journal of Geology, v. 111, no. 1, p. 89–108.

Law, Carol, 2011, Northern Mozambique—True “wild-cat” exploration in east Africa: American Association of Petroleum Geologists Search and Discovery article 110157(2011), 39 p.

Nairn, A.E.M., Lerche, I., and Iliffe, J., 1991, Geology, basin analysis, and hydrocarbon potential of Mozambique and the Mozambique Channel: Earth-Science Reviews, v. 30, no. 1–2, p. 81–124.

PetroSeychelles, 2013, The Seychelles licensing initia- tives: NAPE, February 5–8, Houston, Texas, 46 p., http://www.internationalpavilion.com/NAPE%202013%20Presentations/Seychelles.pdf.

Ophir Energy Company, 2007, Hydrocarbon Prospectively of Deepwater Southern Tanzania—East African Petroleum Conference: Arusha, Tanzania, March 7–9, 2007, 26 p.

http://energy.cr.usgs.gov/oilgas/noga/

http://www.ogj.com/articles/print/volume-98/issue-33/exploration-development/tanzanias-mafia-deepwater-basin-indicates-potential-on-new-seismic-data.html

http://envoi.co.uk/wp-content/uploads/2012/11/P191WessexSEAfricaJuanDeNovaSynopsis.pdf

http://www.internationalpavilion.com/NAPE%202013%20Presentations/Seychelles.pdf

References 13

Ophir Energy Company, 2011, Exploration in Tanzania and Madagascar—Evolution Securities East Africa Conference: London, January 13, 2011, 27 p.

Reeves, C.V., Sahu, B.K., and de Wit, M., 2002, A re-examina-tion of the paleo-position of Africa’s eastern neighbours in Gondwana: Journal of African Earth Sciences, v. 34, no. 1, p. 101–108.

Rusk, Bertagne & Associates, 2003, Petroleum geology and geophysics of the Mozambique Channel, executive sum-mary: 20 p., http://www.petrocommunicators.com/moz/index.htm. Last accessed March 6, 2012.

U.S. Geological Survey Geologic Names Committee, 2010, Divisions of geologic time: U.S. Geological Survey Fact Sheet 2010−3059, 2 p.

U.S. Geological Survey World Conventional Resources Assessment Team, 2012, An estimate of undiscovered conventional oil and gas resources of the world, 2012: U.S. Geological Survey Fact Sheet 2012–3042, 6 p. Available at http://pubs.usgs.gov/fs/2012/3042/

Walford, H.L., White, N.J., and Sydow, J.C., 2005, Solid sedi-ment load history of the Zambezi Delta: Earth and Planetary Science Letters, v. 238, no. 1–2, p. 49–63.

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